Central Texas Field Stops

The rocks of the Texas Hill Country bear witness to the story of a dynamic and constantly changing Earth and reveal the existence of ancient mountains, inland seas, earthquakes, uplift, and power of water to dissolve hard rocks. The legacy of this complex history began more than a billion years ago and is represented by the rugged karst terrain of the Texas Hill Country, granite domes that poke above the landscape, scenic rivers flowing from the northwest to the Gulf of Mexico, crystal clear springs, a wealth of mineral resources, and the fossils of small organisms that flourished in ancient seas.

Traveling southeast from the Llano Uplift toward Austin, one crosses the Edwards Plateau. Composed of limestone that formed a carbonate platform in under a shallow ocean in the Cretaceous Period, the Edwards Plateau was uplifted during the region's complex geologic history. The Balcones Escarpment, an old fault zone, marks the eastern and southeastern boundaries of the Edwards Plateau. The Balcones Escarpment cuts across Austin and is the divide between east and west Texas.

In the Pleistocene Epoch in the late Cenozoic Era, numerous glacial and interglacial periods influenced the climate of Central Texas and made their mark on the landscape. Large mammals roamed the prairie grasslands of Central Texas during the Pleistocene Epoch. The fossil remains of a nursery herd of Columbian mammoths that likely met their demise in a flash flood event approximately 67,000 years ago are preserved at the Waco Mammoth National Monument, a paleontologic research site.

A watershed, or drainage basin, collects water from rain and snowmelt and funnels it downslope into waterways such as streams, which in turn convey the water to larger rivers, lakes, playas, wetlands, estuaries, or the ocean. Several large rivers traverse Central Texas as they flow to the Gulf of Mexico. They shape the land surface through physical and chemical weathering, erosion, transport, and deposition. The Colorado River, which flows through Austin, is the longest Texas River (1,387 km). In the Hill Country, a series of reservoirs on the Colorado River make up the Highland Lakes System. These reservoirs store water for use by people, businesses and industries, provide hydroelectric power, and offer recreational opportunities for boating, fishing, and camping.

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