Caprock Canyon Geology

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Caprock Canyons Geology

Writen by: Mike Long

When peering into the depths of the canyon system located within Briscoe County, one experiences the sensation of magnificence and wonder. The forces that produced such a chasm are the results of geological time and the reshaping of the earth’s crust. The crust is the solid outer layer of the earth. Its relative thickness to the earth can be compared to the thickness of the skin of an apple. Below the crust is a vast reservoir of heat energy. This heat warps and breaks apart the crust producing mountain ranges, seas, valleys, volcanoes, and earthquakes. Wind, water, and chemical reactions cause the weathering of rocks in the high elevations breaking the rock into sediment. The sediments are then transported by erosion to lower elevation forming sedimentary rocks. Here is where our story begins of the geological history of the Briscoe County canyons.

The various rock layers that are exposed within the Briscoe County canyons represent 230 million years of geologic history. It took hundreds of thousands, to more than a million years to carve out the canyon gorges trough ancient deposited sediment layers. There are four major time periods of earth’s history represented by the sedimentary rocks exposed within the canyons. They are the Permian, Triassic, Tertiary, and Quaternary timelines.

The Permian Period (230 million years ago) is seen at the bottom of the deepest canyons. It is called the Quartermaster Formation. This formation is easily recognized by its brick red to vermilion color. This layer represents a shallow sea that evaporated when it became land locked. Bright red shale, lenses of grey shale, clays, mudstone and sandstones are found within the Quartermaster Formation. Veins of gypsum were deposited from the evaporating sea. The gypsum is a salt that dissolves and enters some local aquifers producing “gyp water”. Since the Permian sea was evaporating, the water became extremely salty. This was not conducive for life, so fossils are limited.

The Triassic Period is seen above the Quartermaster Formation. The Triassic sediments were deposited when a mountain range formed in what is now South Central Texas. This uplifting event is the Ouachita Orogeny. Sediments were carried to this area by water erosion. The two layers that represent the Triassic Period are the Tecovas (lower) and Trujillo (upper) Formations. The Tecovas Formation averages about 200’ in thickness. It consists of multicolored shale with thin layers of sandstone. Fossils found within the Tecovas indicated that swamps and streams dominated the area. Fossils include phytosaurs (alligator-like reptiles), Buettnerias (giant amphibians), and petrified wood. Minerals found within this zone include hematite, psilomelane, concretions with veins of calcite, and geodes. There is also jasper found that the Indians used as tools and points called Tecovas Jasper.

Resting on top of the Tecovas is the Trujillo Formation. The transformation between the Tecovas and Trujillo is easily located due to a Trujillo sandstone layer at the junction. It readily forms a cliff between the two zones. The Trujillo makeup consists of pebble-sized rocks and fragments. This indicates a strong current of water flowing over the surface. Also are found red and green shale that indicates times of less water current. Fossils found in the Trujillo include Buettneria, leaf imprints, mineralized wood, reptilian teeth and bones. Hoodoos (pedestals of rock) can be seen due to the differential erosion of the shale and sandstone.

The Tertiary Period indicates a different direction of water flow into this region. Out west, the Laramide Orogeny occurred. This event uplifted the crust, which gave rise to the Rocky Mountains. It is estimated that the taller peaks were as high as 20,000’ above sea level. Sediments eroded and then were transported by streams to this area producing the Ogallala Formation. The lower portions of the Ogallala Formation consists reddish-brown fine to medium sandstone, pebbles, cobbles, and conglomerates. The upper portion of the Ogallala Formation is caliche. The caliche layer forms the Caprock. The Caprock is readily seen near the top of the canyons. It usually forms the upper most cliffs of the canyons. Minerals within the Ogallala include florescence opalite, chert, caliche, and various silicate rocks washed from the Rocky Mountains to this area. The Ogallala Formation genesis occurred during a time called the Age of Mammals. Some of the mammal fossil remains include the saber-tooth tiger, the elephant-like shovel-jawed mastodon, giraffe-like camels, and three-foot long tortoises. The Ogallala Formation is water charged in its lower regions and represents an important aquifer for this area.

The Quaternary Period is located in the top layer of the canyon. The Pleistocene Epoch represents this canyon layer.

The Pleistocene sediments were deposited within meandering streams. The landscape consists of lakes, ponds, and large areas of grass. Wind also blew in sediments producing the reddish “blow sands” located at the top rim of the canyon. The Pleistocene is marked by several Ice Ages. In one of the four Quaternary Period glacial events, glaciers advanced as far south as Kansas. The local climate was generally cool. Fossils found in the Pleistocene include the woolly mammoths, mastodons, giant ground sloths, woolly rhinoceros, giant short-faced bears, wolves, Scott’s horses, and bison. Given this area’s fresh water canyon springs and playa lakes, life flourished on the Pleistocene landscape. Directly above the Pleistocene is the Holocene Epoch. The Holocene consists of more recent deposits and is the time when man first migrated into the area.

When looking into the canyon chasm, one can’t help but feel amazement for the forces of nature. Each layer is a page in the geologic history of the Earth. The book has not yet reached the final chapter, for the forces of nature continue to this very day. I have been fortunate in that I’ve hiked these canyons since I was a young boy. In my short time on earth, I have witnessed changes within the canyons. Large rock structures have collapsed over time and with gravity. They are now at the bottom of the canyon subjected to stream erosion. Their sediments will eventually be deposited within an ocean basin. This deposited sediment will, in the far future, experience uplifting and erosion. This will produce an entirely new system of canyons. Nature is still in the process of sculpting its grand design.