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HSB's NATURAL APPEAL - GEOLOGICAL PARADISE.
HSB IS A GEOLOGICAL PARADISE!
Published chapter-by-chapter in the HSB BEACON newspaper, beginning July 2006. hoping to explain why much of the attraction and appeal people feel
for the HSB portion of the Texas Hill Country
is directly attributable to it being a Geological Paradise.
By Ken G. Martin, M.S. Degree in Geology, University of Texas, 1961.
1) Introduction.
2) Basics.
3) Still Peering Through HSB’s Geologic Window.
4) The "Himalayas” of Texas.
5) The Llano Uplift.
6) The Rise of the Llano Uplift.
7) The Central Mineral Region.
8) Austin's Vanishing Mountain Range.
9) Why There’s a Marble Falls.
10) The Canyon of the Colorado, part 1.
11) The Canyon of the Colorado, part 2.
12) Inundating the Llano Uplift.
13) Regional Physiographic Map.
14) Forming the Texas Hill Country.
15) Exhuming the Canyon of the Colorado.
16) Why the Canyon of the Colorado Is So Special.
17) Granite, Granite Gravel & Granite Boulders.
18) Geologic Map of HSB.
19) The Geology of HSB and Its Five Golf Courses.
20) Summary: What our Area’s Geological History Tells Us.
10) The Canyon of the Colorado. Part 1.
In our prior section, we explained: 1) how the HSB-Marble Falls Fault, the largest fault in The Llano Uplift, along which up to a mile of vertical movement occurred 245 million years ago, caused the two towns to be named after rocks; 2) how the Colorado River also played a role in how the communities were named; 3) how the Marble Falls Limestone is the hardest and most resistant rock in the entire Llano Uplift; 4) why “The Falls on the Colorado” is called the Marble Falls; 5) why the Marble Falls Limestone is “Why There’s a Marble Falls;” 6) why there would be neither “The Falls on the Colorado” nor the city of Marble Falls if not for the HSB-Marble Falls Fault Block; 7) why Marble Falls’ “marble” falls is not marble; and 8) how the Marble Falls Limestone was mistaken for marble.
As the Colorado River cut a path ever so slowly from west to east, from upstream to downstream, across the HSB-Marble Fall’s Fault Block and the Marble Falls Limestone’s extremely resistant outcrop belt, it left the “marble” falls as a residual impediment in the river bed, clear evidence of the formation’s exceptional resistance to erosion.
In the process, the hard limestone was polished in sandblasted fashion by river-borne silt and sand-size particles, causing it to resemble marble - the metamorphic equivalent of limestone. However, although hard enough to take on a polish, the Marble Falls Limestone, named for its outcroppings along the river at Marble Falls, is a mere sedimentary rock. It is indeed rare that a sedimentary rock proves hard enough to show polish.
There is one other story that needs to be told regarding the Marble Falls Limestone. With invaluable assistance from the river, another landmark stands as further evidence of how the formation slowed and impeded the denudation of The Llano Uplift like nothing else.
That landmark, The Canyon of the Colorado, stands just downriver from the Highway 281 Bridge at Marble Falls. This Canyon is exceptionally significant. You’ll be surprised at the important role it has played in the post-Paleozoic geological history of our region. You’ll be doubly surprised to see the strong evidence indicating The Canyon is older than North America’s most famous - the Grand Canyon. And if that is an attention grabber, what about if it were 50 times older?
First of all, the main portion of the Grand Canyon is widely recognized to be no more than about five million years old. It formed as the Colorado River, the one that drains westward to the Pacific, responded to the rise of the Kiabab/Colorado Plateau. As the Plateau rose, the river cut ever deeper and worked continuously headward. A canyon 277 miles long, 5,000 feet deep and 10 miles wide stands as a result. The base of the canyon averages 2,200 feet above sea level, indicating there’s room for more work ahead.
The Canyon of the Colorado is a mere 330 feet deep and three-fourths of a mile wide. But then again, the base of the canyon is only 660 feet above sea level at Starke Dam. And the canyon is also only five miles long, being contained entirely within the HSB-Marble Falls Fault Block.
But, it’s not the size of the dog in the fight, it’s the size of the fight in the dog. Although a midget in size, it is 50 times older, Ram-tough, the grand old man of canyons, with 250 million years of experience, the trunk of the family tree of canyons.
Say, that’s quite a claim to fame. How could that be. Well, it’s a more complicated story than that of the Grand Canyon, so bear with me.
When Austin had its six-mile high Ouachita Mountain Range during the Permian Period, drainage off the range’s western slope flowed into the deep basins of West Texas. By the end of the Permian, the mountain range had begun to collapse into the giant rift that formed as the North and South American continents drifted apart for the final time.
This continental drifting, which continues around the world today, is caused by strong convection currents within the underlying molten interior upon which the continents float.
Development of the rift let the ancestral Gulf of Mexico intrude into the Austin area and as the rift widened, it swallowed the mountain range, freed The Llano Uplift to begin rising, all of which produced a 180-degree shift in the direction of drainage. As eastward-flowing runoff began heading toward the nearby Gulf, Texas’ ancestral Colorado River system began to develop.
With the center of The Uplift being eight miles southwest of Llano, the quickest, most straight-line route from there to Austin and the Gulf went through where Marble Falls is located today. The river soon cut a channel through the relatively soft Smithwick Shale cover and bingo, there was the underlying Marble Falls Limestone, the most resistant formation in all of The Llano Uplift, ready to impede its way.
The river soon learned there was no gap through which it could circumvent the hard, sedimentary formation. It would have to cut a path through it at the town site of Marble Falls. The battle was engaged!
The contest would be contained within the HSB-Marble Falls Fault Block, trending SW-NE, extending from HSB thru Marble Falls. Though only 2½ miles wide where the river took it on, the fault block would prove the toughest, most formidable stretch that the river would ever encounter - even as it eventually grew over time to extend across the entire state, from eastern New Mexico to the present Gulf of Mexico.
From its beginning 250 million years ago, The Canyon of the Colorado has served as a stationary funnel through which more than 90 percent of The Llano Uplift’s eroded detritus has been carried to the Gulf.
It has functioned in this manner for two separate, discontinuous periods: 1) for a 125 million year period beginning 250 million years ago, which includes all of the Triassic and Jurassic Periods and the initial portion of the Early Cretaceous; and 2) it went back to work a second time, permanently, about 20 million years ago.
The fact that it was out of service for a period of about 105 million years is another story worth telling. We’ll get into that real soon, but there's another story that's more pressing. Did you know the HSB-Marble Falls Fault Block probably housed two separate and completely distinct waterfalls during much of its initial 125-million-year period of service?
Yep, shore nuf! We'll get into that in our next entry.
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11) The Canyon of the Colorado; Its Bigger, Downstream Waterfall. Part 2.
In the prior chapter, we began studying The Canyon of the Colorado, which stands just downriver from the Highway 281 Bridge at Marble Falls. It was surprising to see the important role it apparently played in the post-Paleozoic geological history of our region.
Better yet, it borders on amazing to see such strong evidence indicating The Canyon of the Colorado could date back 250 million years, which if so, would make it 50 times older than the granddaddy of them all – the Grand Canyon, which is only five million years old.
Whereas the Grand Canyon is 5,000 feet deep and 10 miles wide stands as a result, the Canyon of the Colorado is a mere 330 feet deep and three-fourths of a mile wide. Whereas the Grand Canyon is 277 miles long, The Canyon of the Colorado is only five miles long.
Whereas the base of the Grand Canyon averages 2,200 feet above sea level, the base of The Canyon of the Colorado is only 660 feet above sea level at Starcke Dam.
This makes The Canyon of the Colorado the more nearer of the two to its erosional base level, considering the relatively distances the two canyons are from their river’s ultimate destinations - the Pacific and the Gulf, respectively. This means the Grand Canyon is dealing with a much stronger downward erosional force, amplified by the fact that the plateau it is entrenching into is still rising.
The five-mile long canyon, carved by a meandering river that became entrenched, is contained entirely within the HSB-Marble Falls Fault Block. From our in-depth study of this fault block over the past couple of weeks, we know this fault block is home to the Marble Falls Limestone, the densest, hardest, most resistant rock formation in the state.
Though only three miles wide where encountered by the river, this fault block has proved the toughest, most formidable stretch the Colorado River has ever encountered in its 250 million-year old history - even as it grew over time to extend across the entire state, from eastern New Mexico to the present Gulf of Mexico.
When the river crossed the NE-SW trending HSB-Marble Falls Fault and encountered the HSB-Marble Falls Fault Block, a battle ensued. The Marble Falls, for which the city is named, were created as the river cut ever so slowly into the top of the Marble Falls Limestone – the formation doing its best to inhibit flow.
Obviously, the river eventually prevailed, cut through the entire fault block, and carved The Canyon, leaving both features behind as evidence of a well-fought battle. The Marble Falls are covered today by Lake Marble Falls.
During The Canyon’s early life, a second, truly magnificent waterfall developed at its downstream end, falling off the fault escarpment on the east side of the fault block. Strong evidence off its prior existence remains today.
In fact, the waterfall remains today in a hidden form, being apparent and measurable only by examining the base of the river’s channel, which drops abruptly at least 125 feet precisely as it exits The Canyon.
When this second waterfall was at its most majestic prime, some 200 to 225 million years ago, it probably had as much as 500 feet of fall, as measured from the fall’s brink to the bottom of its splash pan or scour hole at the base of the fall. If it existed today as it did in its prime, it would be ranked as a world-class attraction.
Further evidence reflecting the existence of a major waterfall at this location includes: 1) the fact that the HSB-Marble Falls Fault Block stands as a high escarpment versus its low-lying, downstream neighbor, which is topped with soft Smithwick Shale; 2) the Bluebonnet Hole, a huge cone-shape scour hole located in the base of the river immediately beyond The Canyon’s immediate downstream edge. The top of this cone is 500 feet in diameter, and it is still over 125 feet deep; 3) the presence of huge, harbor-like valley immediately downstream from the fault block that has been carved out of the softer Smithwick Shale by the turbulent waters; and 4) the presence of extensive gravel deposits that fill much of this valley today.
Last week, we discussed the fact that from its beginning 250 million years ago, The Canyon of the Colorado has served as a stationary funnel through which more than 90 percent of The Llano Uplift’s eroded detritus has been carried to the Gulf of Mexico or its ancestral equivalent.
The Canyon functioned in this manner for two separate, discontinuous periods: a) for a 125 million year period beginning 250 million years ago, which includes all of the Triassic and Jurassic Periods and the initial portion of the Early Cretaceous; and b) it went back to work a second time, permanently, about 20 million years ago.
The fact that The Canyon was out of service for a period of about 105 million years is another story worth telling. We’ll get into that in our next chapter, when we look at the “Inundation of the Llano Uplift.”
You’ll be surprised to learn not only why The Canyon was out of service for such a long period, but that the ground you walk on today was buried under a half-mile or more of Cretaceous-age sediment when the dinosaurs died off 66 million years ago.
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12) Inundating The Llano Uplift.
We have discussed how during the early-most Triassic Period, the segment of the Ouachita Mountain Range located between the Red River and West Texas, and which trended through Austin, collapsed into the widening abyss - a rift zone - created as the two American continents drifted apart, forming the initial stage of the ancestral Gulf of Mexico.
In addition to effectively eliminating the huge mountain range as the rift did when it began forming 250 million years ago, the corresponding release of compressive pressure freed the Llano area from the range’s entrapment and The Llano Uplift began to rise.
As The Uplift rose during the Triassic, erosion began denuding The Uplift area and drainage begin to flow eastward to the sea now lapping at the shores of Austin, sitting as it was on the western edge of the rift that had formed at the North American continent’s then southeastern margin.
During the preceding Permian Period, drainage in the Llano area had been towards west Texas, flowing off the west flank of the high Ouachita Mountain Range.
Once the eastward flowing ancestral Colorado River developed, it began cutting The Canyon of the Colorado as it flowed toward Austin, carrying sands and gravels eroded from The Uplift area. These sediments, which help abrade The Canyon, were deposited as deltas built out into the rift area eastward from Austin area’s shoreline.
This process continued through the Triassic Period and into much of the Jurassic. Toward the end of the Jurassic, worldwide sea levels began rising, encroaching upon the continent. The seas would reach record heights in the Cretaceous Period that followed, before receding from central Texas at the end of the Cretaceous about 65 million years ago.
By about 125 million years ago, the rising Cretaceous sea entered The Canyon of the Colorado, dropping sand and gravel eroded from The Llano at the bottom of the river, gradually filling the channel, just as the sea had been doing as it had worked its way (transgressed) upstream from Austin.
As the sea continued its march upstream, it soon drowned The Canyon with sediment, and eventually covered the entire The Llano Uplift, which at its high point is about 1,200 feet higher than the base of The Canyon.
Offshore from the basal, deltaic sand/gravel sequence being deposited by the transgressing sea, a sequence of Cretaceous limestone formations precipitated from the sea. The flat-lying, soft, chalky, Cretaceous limestones make up most of today’s Hill Country. They typically vary from zero to about 500 feet thick.
The thickest and youngest portion of this Early Cretaceous sedimentation is found in the ancestral Colorado River valley, which was by far the most deeply incised of the pre-Cretaceous valleys that formed off The Llano’s east flank prior to the transgression.
Here the total preserved sedimentational sequence totals about 750 feet, with the lower 250 feet representing that earlier section that outcrops nowhere else in the area.
Today, the rich basal deltaic sequence is best seen outcropping along the Pedernales River between Fredericksburg and Stonewall. And, you guessed it; the Wildseed Farm people learned of these rich soils and set up its seed farming business there in the late 1990s.
This fertile, loamy sequence ranges from zero up to 225 feet thick, its varying thickness being partially due to irregularities on the unconformable pre-Cretaceous surface.
The Llano Uplift continued to slowly and gently rise through Triassic, Jurassic and Early Cretaceous times. Its highest portions were likely continuously above sea level until finally covered by deposition of the Austin Chalk during the Upper Cretaceous. At that Late Cretaceous time, about 80 or so million years ago, practically all of Texas was covered by the sea.
The sea retreated from our area, permanently, at the end of the Cretaceous, some 65 million years ago. By that time, our area had been buried by a huge amount of Cretaceous sedimentation. For example, if one were around then to measure its depth on the downstream side of Starke Dam, he would likely have found it to be at least a half-mile deep.
In our next section, we move forward in time to the Miocene Epoch, lasting from 15 to 27 million years ago, and begin taking a look the relationships between The Edwards Plateau, The Texas Hill Country and The Balcones Fault System.
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13) Regional Physiographic Map.
To get acclimated to the regional setting, please refer to the accompanying colored physiographic map of central Texas, shown above, which locates the Edwards Plateau, the Texas Hill Country, the Llano Uplift, the Highland Lakes and the Gulf Coastal Plain. Note that the Balcones Fault, a zone of down-to-the-coast faulting that developed between 15 and 25 million years ago, parallels the outer eastern and southern margin of the Hill County.
Its location so closely follows the path of I-35 that it is not mapped independently. Its significance arises from the fact that it separates the flat and low-lying Gulf Coastal Plain from the flat and high-standing Edwards Plateau, which lies to the west and extends into West Texas.
The Hill Country is a relatively recent development and a direct product of the Balcones Fault. If the Fault had not caused the Edwards Plateau to stand higher than the Coastal Plain, there would be no Hill Country.
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14) Forming the Texas Hill Country.
Please refer to the accompanying map of central Texas (see the front of the booklet), which locates the Texas Hill Country, The Llano Uplift, and The Highland Lakes. Also take note that the Balcones Fault, a zone of down-to-the-coast faulting that developed between 15 and 25 million years ago, parallels the outer eastern and southern margin of The Hill County and closely follows the path of I-35.
The relatively flat-lying Gulf Coastal Plain lies east of the Balcones Fault, whereas the higher Edwards Plateau extends westward into West Texas. The Hill Country is a relatively recent development, having been carved through headward erosion by streams that have moved upstream and cut into the outer edges of the Plateau since the Balcones faulting occurred.
In our previous chapter, we discussed how, beginning about 125 million years ago, rising Cretaceous sea began encroaching on The Llano Uplift and as it began doing so, it first entered the more downstream The Canyon of the Colorado.
Sand and gravel eroded from The Llano Uplift area dropped out as the ancestral Colorado River’s current slowed upon encountering the advancing sea, just as had been happening as the sea worked its way upstream (transgressed) from Austin.
As the sea continued its march further upstream, The Canyon was soon clogged with Cretaceous sediment. Eventually, sometime around 80 million years ago, the entire The Llano Uplift was overlapped by such sedimentation.
As the Cretaceous sea transgressed upon The Llano Uplift and laid down the basal blanket of coarse-grained detrital sediments, a sequence of flat-lying, soft, chalky, limestone formations were being deposited contemporaneously therewith offshore from the deltaic deposits and beyond bordering barrier sand bars. It precipitated to the relatively shallow sea floor from seas super-concentrated with calcium carbonate, which was typical of the Cretaceous seas.
The Llano Uplift continued to slowly and gently rise through Triassic, Jurassic and into Late Cretaceous times. The Uplift’s highest portions were likely continuously above sea level until finally covered by deposition of the Austin Chalk. At that Late Cretaceous time, about 80 or so million years ago, practically all of Texas was inundated.
The sea retreated from Texas, permanently, at the end of the Cretaceous Period, some 65 million years ago. By that time, our area was buried under a thick cover of Cretaceous sedimentation.
For example, if one were around then to measure the depth of this cover where the U.S. 281 bridge crosses the river today, he would likely have found it to be at least a half-mile deep, and possibly as much as twice that depth.
After the Cretaceous sea retreated, a slightly eastward-sloping plain was left behind, draining sluggishly in a Gulfward direction. A system of small, slow-moving meandering streams developed.
Gradually, over the next 40 to 50 million years, the relatively flat-lying Austin Chalk and younger Cretaceous sediments were eroded away, leaving a lower but still relatively flat-lying plain composed of more resistant uppermost Lower Cretaceous limestone.
Beginning about 25 million years ago, subsidence in the Gulf Coast Basin reawakened the rift zone buried beneath Austin that had been inactive for about 175 million years. The basin-wide subsidence led to extension along the basin’s upper margin.
In the central Texas area, it produced a regional, down-to-the-coast fault system trending from Waco south through Austin, San Marcos, New Braunfels, San Antonio and westward to Uvalde and beyond.
The fault zone, typically 10 to 15 miles wide, is known today as the Balcones Fault System. In central Texas, I-35 typically lies a couple of miles east of the fault's primary escarpments.
The system is comprised of a series of normal faults lined up in echelon, with its trend more or less paralleling the Gulf of Mexico’s shoreline.
About 40 miles east and south of the Balcones System, a compensating up-to-the-coast fault system developed at this same time, paralleling the Balcones. This fault zone, known as the Luling-Mexia Fault System, formed the basinward side of a huge regional graben.
The extension-produced graben system brought forth even more resemblance to the underlying, huge buried rift that had formed 225 million years earlier, when the American continents pulled apart.
In this manner, the Balcones System, which formed at the edge of the ancestral margin of the North American continent, help provide equilibrium between the weaker, subsiding Gulf Coastal Plain located east and south of the Balcones and the stable platform-like area to the west and north.
After about 10 million years of adjustment along these two paralleling fault systems, equilibrium was finally established. There has been no movement along the two fault systems since that time.
Approximately 1,750 feet of down-to-the-coast vertical movement occurred along the Balcones System before equilibrium was reached. Today, fault escarpments related to the Balcones System separate the Gulf Coastal Plain to the east and south from the higher Edwards Plateau located to the west and north. However, due to subsequent erosion, which was obviously differential in nature, the top of the Plateau today stands no more than about 700 feet higher than the adjacent Coastal Plain.
Once faulting commenced and the area west of Austin and north of San Antonio began to stand higher, the ancestral Colorado River and other ancestral Llano Uplift drainage systems went back to work and began cutting sharply upstream, incising their way into the Plateau through headward erosion, trying to adjust the Plateau’s drainage system to the lower erosional base level of the Coastal Plain.
Save for The Llano Uplift, these lower Cretaceous limestone formations make up most of the outcrops in today’s Texas Hill Country. In The Llano Uplift, they and their basal sandy section, which typically range up to 500 feet thick, collectively, rest with angular unconformity on top of the Paleozoic sediments and Pre-Cambrian metamorphics and granites.
These carbonate sediments that typically outcrop in the Texas Hill Country make for especially appealing scenery. They are capable of standing tall, with higher more vertically walled river channels than seen in the broader, more rounded valleys that The Llano Uplift’s granite and metamorphic rocks outcrops typically produce.
Next week, we’ll try to locate, dig out, revisit and get The Canyon of the Colorado up and running again. When we last discussed The Canyon, it had been buried some 65 million years ago, under somewhere between 2,500 to 5,000 feet of sediment. We know from past history, such as during the period from 250 to 125 million years ago, that The Canyon has proven to be the principal route for hauling detrital material eastward out of the region.
That being the case, it is the region’s only hope for digging out The Llano Uplift, for making the Highland Lakes possible and to give us the Hill Country as we know it today. We’ll grow to understand that our collective, present-day dreams of a wonderful future for HSB and Marble Falls, based on having these three elements to enjoy, would have remained forever buried if not for The Canyon.
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15) Exhuming The Canyon of the Colorado.
We have previously discussed how The Llano Uplift began slowly rising at the end of the Permian Period, about 250 million years ago. The Uplift continued to rise through the Triassic and Jurassic Periods and into the latter portion of the Cretaceous Period. It stabilized and stopped rising relative to the surrounding region soon after the deposition of the Austin Chalk, about 75 to 80 million years ago.
After the Cretaceous sea retreated from central Texas about 65 million years ago, a slightly eastward-sloping plain was left behind, draining sluggishly toward the Gulf. A system of small, slow-moving meandering streams developed.
Gradually, over the next 40 to 50 million years, the relatively flat-lying Austin Chalk and younger Cretaceous sediments were eroded away, leaving a lower but still relatively flat-lying plain composed of the more resistant uppermost Lower Cretaceous limestone formations that cap today’s Edwards Plateau.
That’s when the Balcones Fault System developed in the Austin area, beginning about 25 million years ago. Vertical movement occurred along the fault line for
about 10 million years. The Fault dropped the Gulf Coastal Plain down at least 1,750 feet, separating it from the Edwards Plateau.
Beginning with the Cretaceous Period, 145 million years ago, the sea began transgressing onto the largely long-exposed and heavily eroded surface of the North American continent in a world-wide sea level rise that would eventually attain the highest sea level in the earth’s history.
During the preceding 105 million years of denudation, the erosional surface in central Texas had been shaped by ancestral streams such as the Colorado and Pedernales rivers that had developed and were flowing southeastward off emerging The Llano Uplift.
It took the sea about 20 million years to move inland and encroach upon what we know today as The Canyon of the Colorado at Marble Falls. The sea had to rise high enough to move 50 miles inland from Austin, which was then still located on the ancestral Gulf of Mexico’s shore on the continent’s outer margin and at an elevation probably about 300 feet lower than The Canyon.
The ancestral Gulf had moved westward to the Austin locale after the Ouachita Mountain Range collapsed into the huge rift that formed when the North and South American continents disengaged and drifted apart during the early Triassic.
The sea advanced on a pre-Cretaceous surface that had been exposed to erosion continuously since the close of the Permian. When the advancing seas reached the Marble Falls area about 125 million years ago, the then pre-existing erosional surface had as much as 640 feet of topographic relief as proven by examining present-day outcrops along a line from Burnet south through Marble Falls to Johnson City.
The Canyon of the Colorado occupied the deepest incision into this ancient surface, indicating it had been the preferred and most used channel heading southeast from The Llano Uplift.
The pre-Cretaceous surface stands today much like it probably did 125 million years ago. It is about at an elevation of 1,300 feet at the Courthouse Square in Burnet. From there it slopes very gradually southward to Marble Falls at the rate of 25 feet per mile.
Marble Falls’ high school, which is located 12 miles south of Burnet, is built on this same surface. It sets at an elevation of about 1,000 feet and is located a mile and a half north of the center of The Canyon of the Colorado.
From the high school south one mile, the surface’s slope increases from 25 feet per mile to 60 as it begins feeling the presence of The Canyon. From there over the next quarter mile south, the surface drops off into a 280-foot deep gorge that forms the bottom portion of the 340-feet-deep Canyon.
The base of the gorge is only 660 feet above sea level. The base of the river’s channel at Austin is only 235 feet lower, being at an elevation of 425 feet at the I-35 bridge.
This differential of a mere 235 feet signals another important geologic message. It tells all we need to know about how movement along the Balcones Fault occurred, which we’ll get to in a moment.
Going from The Canyon south to Johnson City, the pre-Cretaceous surface gradually rises to an elevation of 1,180 feet at the drainage divide between the Colorado and Pedernales rivers. From there, the 125 million-year-old surface drops gradually into Johnson City, where the Pedernales River’s channel is 1,060 feet above sea level – 400 feet higher than the base of the gorge at Marble Falls.
As is the case today, the ancestral Colorado and Pedernales were the only rivers draining The Llano Uplift. Considering that the Pedernales’ erosional base level stands 400 feet higher on the ancestral surface than does the Colorado’s at comparable distances from The Uplift and since the Pedernales is draining an area that is largely south of The Uplift, it’s clear that the Pedernales carried no more than a small percentage of the detrital material that has been removed from The Llano Uplift since it began to rise 250 million years ago.
Since rivers seek the quickest route to the sea, which is generally the most direct route, drainage off The Llano Uplift after it began rising 250 million years ago would be expected to have headed southeast toward the Gulf at Austin, whose locale was located along the shore of the ancestral Gulf of Mexico. As pointed out in earlier discussions, Marble Falls is located on a direct line between Llano and Austin.
It was therefore not surprising to find the above described proof that practically all of The Llano Uplift’s drainage came through The Canyon at Marble Falls. The Canyon had been occupied by the ancestral Colorado River for a 125-million-year period beginning 250 million years ago, ending temporarily while The Canyon was filled by lower Cretaceous sediment.
Practically all of the erosional material denuded from the Llano Uplift had been funneled through The Canyon by the ancestral Colorado River.
This data confirms that The Canyon of the Colorado, originating as it did with the rise of The Llano Uplift, is indeed about 50 times older than the Grand Canyon, which is widely understood to have not begun to form until about five million years ago.
However, The Canyon was clogged full of sediment, buried a half-mile deep and completely out of service for a period that began about 125 million years ago. The Canyon did not begin to get cleared out until the Balcones Fault System developed 25 million years ago and began lowering the Gulf Coastal Plain, which extends from the Balcones Fault Zone at Austin southeastward to the Gulf of Mexico.
In earlier sections, we saw there had been at least 1,750 feet (possibly as much as 2,250 feet) of relative vertical movement along the Balcones Fault Zone, a down-to-the-coast system that was active in the Austin area for a period of about 10 million years. Using 2,000 feet for simplicity sake, this works out to being only 2.4 inches of vertical movement per each 1,000-year time frame while the Fault was active – being during the period lasting from 15 to 25 million years ago.
The fault separated the Gulf Coastal Plain to the east from the Edwards Plateau on the west. What we didn’t get into in earlier discussions regarding the Fault System’s relative vertical movement was how much of it involved an actual rise of the Edwards Plateau and how much involved lowering the Gulf Coastal Plain. Practically all of the movement that occurred along the Balcones Fault system was likely confined to downward movement of the Gulf Coastal Plain.
Late Cretaceous Navarro/Taylor deposition preserved on the Gulf Coast side of the Balcones Fault tells us that The Llano Uplift ceased rising some 75 million years ago and that the region has remained practically stable ever since, with the seas retreating from central Texas at the end of the Cretaceous about 65 million years ago as sea levels declined from their historic maximum experienced during the Cretaceous Period.
If the Balcones Fault had not developed, had not dropped the Gulf Coastal Plain so much, and in the process had not lowered the erosional base level as it did, The Llano Uplift, The Canyon, Marble Falls, HSB and the like would likely remain buried today.
But because all that happened, all of the sedimentation that had covered The Llano Uplift portion of The Hill Country has not been removed, hauled once again down the Colorado River, funneled once again through The Canyon, and once again carried beyond to the Gulf of Mexico.
Based on the nature, age and disposition of the Cretaceous deposition that buried the area, it is highly likely that the aforementioned portion of the Hill Country that has been uncovered closely resembles the physical character of the area before the advancing sea buried it.
Our exhumed and resurrected Canyon is quite a remarkable geologic feature, and is correct in making a second rather audacious claim. While the process of uncovering it did not begin until 25 million years ago, that is still five time older than the Grand Canyon, which to repeat did not begin developing until five million years ago.
In conclusion, The Canyon can make four very legitimate claims: 1) it has been in use, off and on, for a period that is 50 times longer than the Grand Canyon; 2) the resurrected Canyon is five times older than the Grand Canyon; 3) it is one of the few canyons in the world that can be shown so definitely as having had two lives; and 4) it may be unique among canyons of the world in having had two lives that were separated by a such a long period of time – a 100 million years
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16) Why the Canyon of the Colorado Is So Special.
THE CANYON OF THE COLORADO, WHICH BEGAN DEVELOPING AT THE START OF THE TRIASSIC PERIOD, IS ONE OF NORTH AMERICA’s MOST SIGNIFICANT RIVER CANYONS. ALTHOUGH SEEMINGLY UNDERWHELMING IN PHYSICAL STATURE, THE HALF-MILE WIDE, 340-FOOT DEEP, FOUR-MILE LONG CANYON HAS AN EXTRAORDINARY GEOLOGIC HISTORY, AS FOLLOWS:
A) The Canyon is at least four times older than those seen on other rivers in the western U.S.
B) It began developing 50 times earlier than the Grand Canyon, which is a mere five million years ago.
C) The Canyon is carved out of the Marble Falls Limestone, one of the hardest and most resistant geologic formations in the country.
D) The Marble Falls Limestone makes up a narrow, elongated fault block oriented perpendicular to the river. The fault block is bounded on each side by less resistant formations, and therefore stands topographically higher, forming a barrier that has impeded river flow. To reach its intended destination, the Gulf of Mexico, the ancestral Colorado had no other option but to carve the Canyon through the highly resistant limestone fault block.
E) The fault located at the upstream end of the Canyon, just above the “Marble” Falls, has as much as 5,000 feet of normal, vertical movement in the Marble Falls area. This fault is regional in nature and trends NE-SW across the southeast flank of The Llano Uplift. There are few faults in the country that have such a large amount of normal, surface expression. All faults in the Llano Uplift have been inactive for 200 million years.
F) Thinking the 340-foot deep Canyon should be deeper and more physically impressive is unreasonable, considering that the local maximum elevation is only 1,000 feet above sea level, that its base is only 660 feet above sea level, that the channel’s base at Austin is only 235 feet lower (being at 425 feet a.s.l.), and that the Marble Falls Limestone is so resistant to erosion.
G) If the Canyon were carved from any rock formation in The Llano Uplift other than the highly resistant Marble Falls Limestone, there would certainly be no “Marble” Falls at Marble Falls today, the channel at Marble Falls would be 100 to 150 feet deeper, and there would be no trace of The Canyon at Marble Falls just like there’s none like it anywhere else along the Colorado.
H) The Canyon has had two lives: 1) an initial life that began 250 million years ago and which lasted for about 125 million years, and 2) a second life that began about 25 million years ago and continues today. The Canyon was buried and out of service during the intervening 100-million-year period because advancing Cretaceous seas had covered the region with a half-mile thick blanket of sediment.
I) It is rare that canyons can be shown so definitively to have had two separate lives.
J) Among the few canyons in the world experiencing two distinct lives, none are known to have been out of service for such a lengthy period.
K) Practically all of the detritus from the twice denuded Llano Uplift has been funneled through The Canyon, first by the ancestral Colorado River and secondly by the present day Colorado.
L) During The Canyon’s first life, great waterfalls were present at both ends. The upstream waterfall probably closely resembled today’s “Marble” Falls. Although now covered by Lake Marble Falls, one of Texas’ Highland Lakes, this waterfall crosses the river today at a 45-degree angle, bearing NE-SW, beginning at a point just upstream from Marble Falls’ Hampton Inn. From that point, the waterfall dropped about 45 feet over a distance of approximately 100 yards in a series of stair-stepped ledges up to 12 feet high.
M) The ancestral downstream waterfall was a completely different type. It would have had truly magnificent proportions during its peak life, which was about 200 million years ago. Its crest-line was probably about 250 feet wide, free of large boulders, and likely standing around 250 feet high. The water would have fallen without obstruction into a huge underlying catch basin scoured at least 150 feet deep and containing little rubble. Although this waterfall has been long removed through base level erosion, a 500-foot wide and 125-foot deep scour-hole remains in the river bed today as a reminder of its past presence. It is called Bluebonnet Hole.
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17) Granite, Granite Gravel & Granite Boulders.
Earlier in this study, we examined the Geology of HSB in general and why variations in our local geology have helped provide HSB’s five golf courses with such wonderful natural settings. Considering that the 1,100 million-year-old Town Mountain Granite underlies about 42% of the five courses, being beneath 38 of the 90 holes, we thought taking a closer look at granite would be of interest. So this week we will examine where Granite comes from and how Granite Gravel and Granite Boulders are formed.
Enchanted Rock, the best place to study granite in Texas, is located about 16 miles southwest of Llano. It is the second largest granite dome in the US, behind only to Stone Mountain, located outside Atlanta.
Both domes exhibit exfoliation, as does Granite Mountain, the largest granite dome in our immediate area, located just west of Marble Falls. Granite has a strong tendency to weather in this manner. The exfoliated layers at Enchanted Rock, which are thicker than the average man (see below), have a tendency to peel like an onion.
The granite of the Llano Uplift comprises a giant batholith, made of multiple masses (plutons) of magma that traveled toward the surface from a zone of partial melting at the base of the Earth's continental crust, typically about 25 miles thick. Plutons of relatively buoyant http://en.wikipedia.org/wiki/Buoyancy magma are called plutonic diapirs http://en.wikipedia.org/wiki/Diapir. Because the diapirs are liquefied and very hot, they tend to rise through the surrounding country rock http://en.wikipedia.org/wiki/Country_rock_(geology), pushing it aside and partially melting it.
Most diapirs do not reach the surface to form volcanoes http://en.wikipedia.org/wiki/Volcano, but instead slow down, cool and solidify as plutons 5 to 30 kilometers underground. The granite in the HSB area is part of the Granite Mountain Pluton, which is a plutonic diapir.
Assuming the pluton stopped rising while only five kilometers (three miles) underground, we can say the granite in HSB is exposed because erosion removed at least three miles of overburden during the 550 million years of erosion that occurred after the granite intruded 1,100 million years and before the Cambrian seas inundated the area 550 million years ago.
As HSB began coming out of the ground beginning in 1971, one of Norman Hurd’s first acts was to open a granite gravel quarry. He needed road material, foundation material and mineral-rich porous soils for landscaping and knew granite gravel would do a fine job of serving all three purposes.
He picked a quarry site just west of HSB Proper and about one-quarter mile south of RR 2147, knowing it was located within the granite outcrop. The site was covered with a blanket of clayey, granite gravel and, equally important, was a convenient location for his planned construction. He had no idea how extraordinarily deep it would go or that it contained such a wonderful assortment of granite boulders.
The pit, now as much as 45 feet deep and about 420 feet long in its greatest dimension, has been in continuous operation for the past 35 years, delivering about fourteen 12-yard truckloads of material a day, which amounts to about 175,000 truckloads over the 35-year period. The quarry has been owned and operated by Glenn Salem, a local HSB resident, for the most recent third of that period.
As you probably noticed while studying the Geologic Map of HSB, essentially all of HSB Proper located north of Hi Circle South is underlain by granite. With rare exception, such as along creek beds and on the granite monadnock located immediately west of the #2 hole on Slickrock, practically all of it is covered with a blanket of clayey, granite gravel five to 15 feet thick. So with such a wide selection of locations available, it is highly likely that convenience was the principal reason for locating the quarry where it is.
As quarrying began, beautiful granite boulders of tombstone quality began appearing. They are most numerous in a discontinuous band between 15 to 25 feet below the surface.
Why they tend to congregate at this level is not fully understood, but some things are clear: 1) Their presence is probably related to ground water movement; 2) They are not related to a granite dike in decay. In fact, the quarry walls are riddled with one and two inch thick granite dikes that can be traced from the granite gravel though the individual boulders, crossing the band of boulders at a sharp angle.
As quarrying continued, it became apparent the quarry was home to hundreds of boulders in various sizes - a few up to 40 feet long. Norman eventually found some were too big to move without first cutting them in half, such as the one that forms the centerpiece of the waterfall at the Whitewater putting golf course.
Another granite gravel quarry containing boulders was established in Cottonwood Shores, but was never very active. However, both quarries have several common elements, one of the more important being located adjacent to the HSB-Marble Falls Fault System, along which there was about 2,500 feet of vertical movement during the Triassic Period, between 200 and 250 million years ago. Nearness to the fault and the massive amount of groundwater seems critical to boulder formation.
Groundwater would have moved much more freely up, down and along the fault zone than it could have anywhere else in the area. Granite located along the fault was exposed to far more CHEMICAL weathering, which produces a change in mineral composition (decomposition), than encountered by granite located distant from the fault. Near the fault, groundwater attacked blocks of granite from all directions due to the extraordinary groundwater movement, causing the blocks to exfoliate in all directions as ground water penetrated and weakened the block’s outer perimeter. This action ultimately formed a granite boulder.
Since granite is made up principally of quartz and feldspar crystals and since feldspar changes to Kaolin, a common clay, near the fault where it reacts with groundwater, chemical weathering of granite produces a clayey granite gravel.
Granite gravel produced by CHEMICAL weathering generally extends to far greater depths than does granite gravel produced by MECHANICAL weathering, which generally forms a thinner blanket. Mechanical weathering occurs at the Earth’s surface and is produced by the physical action of plants, animals, ice, heat, gravity, running water, and wind.
Now you know where Granite comes from and how Granite Gravel and Granite Boulders are formed.
18) Geologic Map of HSB.
A colored map illustrating the Geology of HSB is included at the front of the booklet. Most of the work should be credited to Dr. Virgil E. Barnes, a well-known field geologist who spent his career with the Bureau of Economic Geology in Austin.
He mapped this area in 1951 and 1952 as part of an exhaustive life-long study of the entire Llano Uplift. His work earned him recognition as the Father of Llano Uplift geology. Thanks also go to Jim Rowe and Shelton Thibodeaux of HSB RE/MAX, who made their copyrighted Street Map of HSB available as a base for this presentation.
This text is intended to go hand-in-hand with the Geologic Map and much of what is presented thereon is explained in NOTE boxes cut into the map. In an attempt to preserve the underlying map of HSB’s streets and golf courses, we’ve used Numerals to identify where geologic formations outcrop in the map area in lieu of coloring in their individual outcrop belts as typically done. Also, we’ve used Letters to identify the two separate fault systems present in the area.
Black lines locate boundaries of the various formally-named Geologic Formations. Blue lines outline black Marble lenses that are present within the Honey Member of the Packsaddle Schist formation. Orange lines identify the location of the three mappable Granite Dikes that intruded into the Honey. Red lines locate where Faults are positioned.
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19) The Geology of HSB and Its Five Golf Courses.
INTRODUCTION: First of all, when did HSB get five golf courses. We all know the Resort is home to the largest Robert Trent Jones Sr. golf complex in America - Slickrock, Ram Rock and Applerock - so that’s three. Escondido’s private Tom Fazio course is the fourth now that HSB’s city limit encompasses the entire development.
Once HSB annexes Skywater, the 1,618-acre development underway between Highway 71 and RR 2147, its fifth will be the Jack Nicklaus Signature Course. It got underway in February 2007. It is scheduled for play in late 2008 and will be operated by the Resort.
Secondly, HSB is the only community in central Texas, save for Kingsland, that is located in all four of the region’s most interesting, desirable, friendly and laid back sectors – the Texas Hill Country, the Llano Uplift, the Central Mineral Region and the Highland Lakes.
In addition, the top of the flat-lying Edwards Plateau, which dominates the physiography of central Texas, holds the high divides just outside the immediate HSB area, offering added interest. These blessings favoring HSB are capped off by the fact that HSB is located on Lake LBJ, the country’s largest constant level lake -America’s lake of choice for those who know.
GENERAL GEOLOGY: Twenty-five million years ago, the HSB area was buried under a sequence of Cretaceous limestone up to 2,500 feet thick. At that time. a regional down-to-the-coast fault system known as the Balcones Fault formed.
It extended from Waco through Austin to San Antonio and beyond. Over the next ten million years, the Fault dropped the eastern, Coastal Plain side of the fault downward, leaving the western, upthrown side of the fault as an uplifted plain which we know today as the Edwards Plateau.
Today, the Plateau stands about 1,000 feet higher in our area than the Coastal Plain’s elevation, where it picks up in east Austin on the Fault’s downthrown side.
Once the Fault formed, subsequent stream erosion worked headward from the lower Plain, with tributaries cutting into the edges of the Plateau and exposing the cream colored, chalky, Cretaceous limestone section. This action eventually produced what we know today as the Texas Hill Country.
The Hill Country is the steeply eroded, eastern portion of the Edwards Plateau. Its northern 20% portion is occupied by the Llano Uplift, an elongated geological dome that weathered into an elongated bowl-shaped region of older rocks of pre-Cambrian and Paleozoic age.
Its Paleozoic rocks are sedimentary in nature, 80% of which is limestone. Its pre-Cambrian rocks have a substantially different origin. They are either igneous (typically granites) or metamorphic (typically schists).
Minerals are usually found in rocks of igneous and metamorphic origin. The portion of the Uplift where these rocks outcrop is called the Central Mineral Region. However, with rare exception, mining in the Region has proved uneconomic.
GEOLOGIC FORMATIONS PRESENT IN HSB: The formations that outcrop in the HSB portion of the Uplift are as follows, from youngest to oldest: 1) the dark gray, typically thin-bedded Honey Member of the pre-Cambrian Packsaddle Schist (1.3 billion years old); 2) the burnt orange, blocky, Sandy Member of the pre-Cambrian Packsaddle Schist (1.25 billion years old); 3) the pink colored, coarse-grained, pre-Cambrian Town Mountain Granite (1.1 billion years old); 4) the brown colored Cambrian Sandstone/Limestone sequence (513 to 550 million years old); 5) light gray Ordovician Ellenberger Limestone and light lavender Dolomite (441 to 513 million years old); 6) the black, petroliferous, Barnett Shale (323 to 338 million years old); 7) dark gray Pennsylvanian Marble Falls Limestone (315 to 323 million years old); 8) the light to dark orangish-brown sandy Pennsylvanian Smithwick Shale (290 to 315 million years old); and rare occurrences in the area’s uppermost tributaries of the 125 million-year-old lower Cretaceous Hensell Sand’s basal conglomerate.
SLICKROCK COURSE: Taking the golf courses by age, oldest to youngest, Slickrock, completed in 1973, is built entirely on igneous terrain, which slopes gently toward Lake LBJ or tributaries thereof.
It is laid out on top of the pre-Cambrian Town Mountain Granite, which is a massive, cylindrical pluton about 10 miles wide and 25 miles long that intruded into the region’s metamorphic strata from the Earth’s molten interior about 1.1 billion years ago. This single granite mass is called the Granite Mountain Pluton.
However, with rare exceptions, such as where monadnocks exist, the granite in HSB is covered by a blanket of granite gravel, its weathered derivative. On Slickrock, granite can be seen outcropping along the creek (Slickrock Creek) where it can be seen on holes #14, #17 and #18 and as a relatively small monadnock that stands above the surrounding terrain immediately west of the #2 tee box.
Holes #12, #13, #14 and #15 run adjacent to and are aligned parallel with Hi Circle South. Running on the immediate opposite side of Hi Circle South is the major HSB-Marble Falls Fault. It is the largest fault in the Llano Uplift and among the largest faults seen at the surface in all of Texas. It crosses Slickrock Creek about 50 feet upstream from the Hi Circle South crossing. The south side of the fault has drop downward about 2,500 feet. The fault has been inactive for about 200 million years.
RAMROCK COURSE: The Ramrock course, completed in 1981 and ranked consistently since then as the most difficult in Texas, requiring precisely located shot-making, has the most colorful outcrops and the most interesting geology of HSB’s four existing courses. It is built entirely on metamorphic terrain, being on the two oldest members of the Packsaddle Schist Formation.
These two - the dark gray Honey and burnt orange Sandy members - are readily identified by color. The Sandy Member is a relatively resistant quartz-feldspar-mica schist that is typically thick bedded. The slightly older Honey Member is softer, thin-bedded hornblende schist that contains several discontinuous lenses of black marble up to 500 feet thick.
The Honey has also been intruded by three granite dikes of mappable size. These highly resistant dikes were injected into the Honey Member under great pressure when the Granite Mountain Pluton intruded the Honey about 1.1 billion years ago. All three are located within 1,500 feet of the Caprock Clubhouse.
The largest dike caps the hill on which the Clubhouse stands. It varies from 10 to 30 feet thick and can be best seen from the #18 greens on both the Ram Rock and Applerock courses. Each dike dominates the terrain where it outcrops.
The Honey has been thrust westward in low-angled to relatively horizontal fashion over the slightly younger Sandy Member, dragging the Sandy to the vertical position as it slid over it.
This pre-Cambrian Thrust Fault, trending NW-SE, runs in front of the #11 green, cuts through the middle of #13 and #14, and splits # 2 in half, tee to green. It also crosses in front of Ramrock’s #3 green and Applerock’s #7 tee boxes.
In central Texas, thrust faults are only seen in the Central Mineral Region’s portion of the Llano Uplift, being products of compressional forces and common in highly folded strata. All other faults in central Texas are of the normal variety, meaning they move vertically - one side up, one side down – being products of tensional forces and non-folded strata.
The Honey Member underlies all of holes #1, #12, #15, #16, #17 and #18, plus the east halves of #2, #3, #11, #13 and #14. Outcrops of the Honey are best seen in the steep-sided gully between tee and green on #12 and where Pecan Creek crosses #16. Lenses of black Marble are present only on holes #17 and #18, where it comprises more than half of the Honey.
The Sandy Member underlies all of holes #4, #5, #6, #7, #8, #9 and #10, plus the west halves of #2, #3, #11, #13 and #14. The Sandy is best seen in the creek bed adjacent to #10 green and along #11 fairway, where it stands vertical both to the right of the tee box and down the fairway about 100 yards on the left.
APPLEROCK COURSE: The Applerock course, completed in 1985, and considered one of the most beautiful in Texas, features the Town Mountain Granite and both members of the Packsaddle Schist. It has the most varied and interesting topography among HSB’s four existing courses. In addition, among HSB’s 72 holes, it has the only ones (#11 and #12) that actually front on Lake LBJ.
The pink colored Town Mountain Granite underlies all of Applerock holes #11, #12 and #13, and all but a small piece of the west portion of #14 and #15. The Town Mountain weathers to a porous granite gravel that produces relatively flat topography, as best illustrated by the Slickrock course.
The dark gray Honey Member of the Packsaddle Schist underlies all of holes #1, #2, #3, #4, #5, #8, #9, #10, #16, #17 and #18, all but the tee boxes on #7, and all but the east part of the #6 green. The burnt orange Sandy Member of the Packsaddle underlies the east part of #6 green and the tee boxes on #7.
Black Marble is present on only two of HSB’s courses, Applerock and Ramrock, and Applerock is home to far more of it than Ramrock. Marble lenses underlie portions of nine Applerock holes, including minor parts of #1, #2, #4, #5, #6, #7, #10, #17 and more than half of #8. A thin granite dike too small to map crosses the #16 fairway near its 150-yard marker, outcropping behind the bunker of the left, and again in Pecan Creek ahead on the right.
ESCONDIDO’s COURSE: Escondido’s Tom Fazio Course, completed in 2006, has received very high marks. Fazio tells locals that although the Escondido course is laid out on very attractive terrain, transected by a beautiful creek that runs year around, a large budget is the main ingredient needed to produce a great course. He says Escondido provided him with the large budget, plus an outstanding natural setting.
Most of the course is underlain by terrain similar to Slickrock’s in that it is built primarily on the Town Mountain Granite. And like Slickrock, it is largely covered by a blanket of weathered granite gravel, with its surface sloping gently toward the lake, or tributaries thereof.
However, all of holes #15 and #16, the west 75% of #14 and the west half of #17, all located in Escondido’s southwest corner, play on the Packsaddle’s Honey Member. None of the Honey outcrops in Escondido contain marble or granite dikes in mappable quantities.
And like Slickrock, the best granite outcrops at Escondido can be seen along the creek (Pecan Creek) as it runs between and parallel with holes #3 and #18. There are also two large granite monadnocks, one of which is the largest in all of HSB.
The monadnocks are residual topographic highs that were left on the ancestral pre-Cambrian surface prior to it being covered by Cambrian sediments 550 million years ago. This surface had been subject to about 450 million years of continuous erosion prior to the Cambrian sea’s advance 550 million years ago.
Granite Mountain, located just west of Marble Falls, is the best example of a granite monadnock in the eastern half of the Llano Uplift and the pluton underlying the Lake LBJ and Lake Buchanan area is named after Granite Mountain.
Escondido, also like Slickrock, has no golf holes with a view of the lake, though it does have about two dozen lots located on the lake. Practically all of Escondido’s lots, save for its Casitas, are larger than the typical HSB lot.
NICKLAUS’ COURSE: The Jack Nicklaus Signature Course and its immediate 1,618-acre area – Skywater - is scheduled to be annexed into HSB by mid-2007. The course, to be completed in late 2008, will be located immediately west of HSB Proper on the south side of RR 2147 and will exhibit the most interesting and varied geology of HSB’s five courses.
It will contain the most interesting geology of any HSB course. It traverses HSB’s full variety of igneous, metamorphic and sedimentary rocks and will cross both of HSB’s two fault systems: A) the NE-SW trending normal, HSB-Marble Falls Fault, which transects across the breadth of HSB, was active between 200 and 250 million years ago; and B) the much older, N-S trending pre-Cambrian Thrust Fault that cuts across the length of HSB West and into the northwest corner of the Nicklaus course. It was active around 1.2 billion years ago.
The course will also have exceptional topographic appeal, ranking with the best HSB offers (Applerock). Ten holes extends up, down and across the rather steep limestone escarpment formed by and located just south of the HSB-Marble Falls Fault.
Running through what we know in HSB as neighborhoods of lake view lots, all ten have views of the lake, twice the amount offered by Applehead. Lots on the NIcklaus course will be larger than those found on the Resort’s three existing courses.
The Nicklaus course will also have three waterfalls, varying from 10 to 20 feet high. The two smaller ones are natural products. A larger artificial waterfall is scheduled for the 20-foot high vertical cliff on the east side of Pecan Creek just off RR 2147, where the par-three #15 hole will be located.
It is laid out to cross the creek where ponded by the dam visable about 150 feet south of 2147. The waterfall will drop into the pond and also be viewable from 2147.
In direct one-on-one, onsite discussions several years ago with Nicklaus’ resident course architect, Chet Williams, held at a time when plans to build the course were on hold and with him fearing it would never be built, he said he thought the course could be the equal of Nicklaus’ gem – Muirfield. Williams had served as resident architect for two other outstanding Nicklaus Signature courses that had been just been completed in central Texas – namely, Georgetown’s Cimarron Hills and Lakeway’s Flintrock Falls.
He said the fabulous natural setting of the HSB course combined the best of the other two courses and expressed frustration at the thought of losing the great personal recognition he could receive if Nicklaus’ HSB course were never built.
Nicklaus’ holes #3, #4, #5, #6, #7, #8, #9, #10, #11 and #12 are laid out south of the HSB-Marble Falls Fault on the north-sloping escarpment held by the Ellenberger Limestone. Holes #3, #4 and #5 work up slope to the top of the ridge.
Holes #6, #7, #8 and #9 play partially back down. Hole #10 takes you back to the top and holes #11 and #12 take you back to the bottom, with the #12 green being only 200 feet up slope from the Fault.
The east third of hole #17, which includes an island green somewhat like the green on Ramrock #4, and all of #18 play on the Town Mountain Granite. Holes #1, #2 and #13 are transected by the HSB-Marble Falls Fault.
The northern part of #1 and #2 overly Town Mountain Granite in proportions 95% and 60%, respectively; the remaining southern portions of each hole overly the Ellenberger Limestone. The Fault divides hole #13 into 70% Ellenberger and 30% Honey, with the Ellenberger portion being on the south.
The pre-Cambrian Thrust Fault cuts across holes #14 and #16, with the east 75% of #14 and the east 90% of #16 being on the dark gray Honey Member. The balance of each is on the Sandy Member.
The west two-thirds of #17 is also on the Honey. Hole #15, being west of the Thrust Fault, is laid out entirely on the burnt orange Sandy Member.
ADDITIONAL GOLFING POSSIBILITIES: A Bruce Devlin Golf Academy and an associated Nine-Hole, Par-Three Golf Course are planned but not yet firm for 114 acres located just west of the Nicklaus course – being at the corner of Highway 71 and RR 2147, opposite Bay Country. The area is underlain by the Packsaddle Schist’s colorful Sandy Member.
If built as currently planned, this development will feature a pro shop, an instructional center and a circular driving range 400 yards in diameter with a tee box circling its entire perimeter.
The uniquely designed circular driving range and tee box would be especially helpful in training golfers to improve their ability to work the ball against all types of conditions. The golf course would be built around two large residential pods containing sites for about 100 Casitas.
MOSQUITOES: Mosquitoes in a study of this nature? You bet! You’ll be surprised how closely related the subjects are.
Have you ever noticed how rare mosquitoes are around Lake LBJ? If so, have you ever wondered why that is? Have you noticed how rare it is to see water standing anywhere in HSB for any length of time? Do you recall that mosquitoes breed in standing, stagnant water?
In describing the geology of HSB’s five golf courses, we called your attention to the fact that all of Slickrock, about 80% of Escondido, about 75% of Applerock, and about 10% of the Nicklaus course are or will be built on porous granite gravel weathered from the underlying Town Mountain Granite.
That is not to imply that the Packsaddle Schist is non-porous. It is highly fractured and indeed porous, just not as much so as a typical five to 15-foot thick blanket of highly porous, granite gravel.
And although the Ellenberger Limestone is not nearly as porous, it is highly fractured. However, of more importance in this regard is the Ellenberger’s positioning, holding the high escarpment south of the big Fault, where it has taken on relatively steep slopes that produce rapid runoffs.
And if you’ve been here for awhile, you’ve also no doubt noticed that practically all of the HSB terrain slopes toward Lake LBJ or a tributary thereof. Water soaks into porous soil and runs off sloping terrain.
It seldom stands on either and when it does, it doesn’t stand for long. HSB has no sizeable area where the terrain is flat and the soil non-porous.
The map also shows that the Town Mountain Granite underlies all of HSB’s lakefront, where 40% of HSB’s 2,400 home sites are built, all of Slickrock’s golf course, which is practically built out. In addition, the remaining part of HSB Proper that is located between the Slickrock course and the lakefront is heavily populated.
Now you know the rest of the story - about 80% of HSB’s home sites are located on sloping terrain underlain by highly porous granite gravel, not places where standing water would be likely or where mosquitoes could breed.
SUMMARY: The geological features discussed in this series are mere examples of a multitude of such that make the HSB-Marble Falls area a Geological Paradise of world-class stature. The Paradise encompasses rocks whose ages date back from 100 million to 1,360 million years, the latter being among the oldest in America. The rocks encompass the entire geologic spectrum – sedimentary, igneous and metamorphic.
The HSB and Marble Falls communities are also privileged with the rare distinctions of being located in all three of central Texas’ most favored locales to live, work and play – The Texas Hill Country, The Llano Uplift and The Highland Lakes.
Since igneous and metamorphic rocks make up the largest portion of The Llano Uplift, and since this portion is known as The Central Mineral Region, this Region constitutes a fourth most-favored area. Although Marble Falls serves the Central Mineral Region to a greater extent than probably any other community, it is actually located completely outside of it, though just barely.
HSB as now constituted is blessed by being totally within the Region, placing it in all four of the most favored. HSB shares this uniqueness with only one other central Texas community – Kingsland.
In addition, HSB has the added good fortune of being located on the most favorable portion of Lake LBJ, the largest constant level lake in the country, if not the world (to confirm, go to Google and type in “constant level lake”) – being America’s lake of choice for those who know.
In summary, we've identified an extraordinary number of natural attractions that bless HSB-Marble Falls and its surrounds. We hope this added in-site helps people better understand our area's wonderfully unique and compelling natural appeal.
It’s no wonder the HSB-Marble Falls area is being recognized as among America’s most premier locales to live, work or play – for a weekend or a lifetime!
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20) SUMMARY: What Our Area’s Geologic History Tells Us.
We hope that this series helped you understand some of the appeal and attractiveness that has drawn you to the HSB area. There is much to appreciate in our wonderful Geological Paradise: the beautiful Hill Country; our one-of-a kind Lake LBJ; our area’s laid back and friendly Heritage; the romance of the Central Mineral Region; that Marble Falls’ Canyon of the Colorado; the HSB-Marble Falls Fault, which is the largest (most vertical movement) seen in all of Texas.
We hope you better understand how central Texas is dominated and was shaped by the Llano Uplift; the mystic associated with HSB-Marble Falls reincarnation – arising as it did from a half-mile deep burial that lasted for 100 million years; and how it is that eastern Llano and western Burnet counties resemble today what the countryside looked like 120 million years ago when dinosaurs roamed the region as shallow Cretaceous seas transgressed its surface, statewide.
Some of our more important geological observations can be summarized by entries A through L as follows:
A) HSB is a geological paradise of world-class proportions, possessing a multi-dimensional window that affords an extraordinarily deep look into the earth’s geologic past. It contains rocks of every era (Cenozoic, Mesozoic, Paleozoic and Pre-Cambrian) and the full spectrum of rocks types (sedimentary, igneous and metamorphic) and provides a look at a broad variety of geologic/geomorphic features and structures. It represents an outdoor laboratory of the highest order and, for that reason, attracts geology students from around the world.
B) The oldest rocks of any kind in the Llano Uplift are metamorphic. They are about 1.4 billion years old and are among the oldest that outcrop in the southern U.S. They comprise the outer perimeter of the North American continent’s early core.
C) The oldest igneous rocks in the Llano Uplift are granite plutons that intruded into the older continental-core rocks about 1.1 billion years ago.
D) We look out from the HSB Chapel and see sectors of today’s surface that are hardly disturbed from what the Pre-Cambrian surface looked like 550 million years ago.
E) We can look at other sectors and see what the surface looked like in Pre-
Cretaceous times. Much of today’s surface outcrop in the HSB area is newly emerged from being covered for 100 million years by Cretaceous cover, pieces of which can still be seen, particularly along incised creek’s above their normal high-water marks.
F) The Canyon of the Colorado, located at Marble Falls, began developing at the beginning of the Triassic Period, 250 million years ago.
G) It is by far the oldest canyon in the western U.S. and ranks among the oldest in the country.
H) The Canyon has had two lives: 1) a 125 million-year life that began 250 million years ago and 2) after being buried for 100 million years, was resurrected and got a second life beginning 25 million years ago.
I) It is 50 times older than the Grand Canyon, which is only 5 million years old.
J) The resurrected Canyon is five times older than the Grand Canyon.
K) It is one of the few canyons in the world that can be shown so definitely to have had two separate lives.
L) It is probably unique among all of the world’s canyons in having had two lives that were separated by such a huge period of time – 100 million years.
In closing the series, we sense a need to get two more pieces of basic information before you. So today we are presenting two maps which we hope will help everyone visualize and more clearly appreciate HSB’s setting – which is the most basic feature of all. The topmost of the two maps identifies the eight principal geologic-geomorphologic sectors of central Texas. For example, it should help explain specifics such as where the Central Mineral Region is located. As seen on the map, it is located in the central portion of the Llano Uplift, where the Uplift’s oldest rocks are located – the Uplift’s igneous (granites) and metamorphic rocks that are all part of the North American continent’s ancestral core, over 1.1 billion years old.
The lower map gives a detailed outline of that small portion of Texas which falls within the boundaries of all four of the state’s most attractive provinces – The Texas Hill Country, The Llano Uplift, The Central Mineral Region, and The Highland Lakes. HSB stands alone among all others cities in Texas as the only city located in this renown Texas “Sweet Spot.”
This map speaks volumes as to why HSB is so special. Although Marble Falls lies just outside the Sweet Spot, we all know it is home to the Bluebonnet Café. Next time you’re there on a half-way decent weekend, look for the motorcycle gangs - those no doubt well-to-do professionals dressed out in motorcycle garb, shades of the Hell’s Angles – breakfasting. You’ll connect the dots and realize they’re there loading on “fuel” before spending the day taking their Hogs for an outing to the Llano Uplift, and through The Central Mineral Region, soaking up the Texas Hill Country and The Highland Lakes in the process.
The Sweet Spot, where they can taste all four regions in one afternoon, is one of their favored drives. The next time you see them out and about, you’ll be reminded that their presence attests to the area’s extraordinary appeal.
And to think that we partake of these extraordinarily beautiful, laid back and friendly environs every day of our lives, saturated as they are with the extraordinary amenities, the championship golf, America’s lake of choice, wonderful people, et cetera, et cetera, et cetera.
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