The Great Plains extends roughly from the Mississippi alluvial plain to the foothills of the Rocky Mountains. The northernmost point enters into Canada just north of Minnesota and North Dakota, while the southernmost point is located in the heart of Texas. For 500 million years, the Great Plains were covered by a shallow ocean between the Rockies and the Appalachian mountains, depositing thousands of feet of sediment along the seafloor. These layers developed slowly into the sedimentary rock and limestone that now run through the Great Plains. 70 million years ago, the vast sea began to drain due to continental uplift leaving behind a nutrient rich, flat plain in the heart of North America.
Better known as the Llano Estacado (Staked Plains) or the Panhandle Plains, the high plains in Texas are a part of a large, flat, elevated plain stretching from West Texas into New Mexico and up to Nebraska. The high plains are marked by an escarpment on each side, the Mescalero on the west and the Caprock on the east. With high elevation and little precipitation, the area is covered in prairie grass. Few trees can be found aside from river basins. One of the most dramatic land formations in the High Plains is the Palo Duro Canyon, carved out by rivers over millions of years.
Fifty million years ago, the Rocky Mountains had immense volcanic activity. The magma and basalt settled down into the Great Plains hardening into slabs of igneous rocks which are much harder than the sedimentary rocks native to the plains. In the Central Texas uplift, the erosion of the soft sedimentary rocks has revealed granite and gneiss. These numerous rock types control the way in which rivers erode the area creating numerous sandstone and limestone mesas throughout the low plateau. The Central Texas Uplift is marked on the eastern edge by the Balcones fault zone and to the north by the Caprock and Mescalero escarpments.
The Edwards Plateau lies west of the Central Texas Uplift and is the most southern part of the Great Plains running to the Rio Grande. Covered in limestone, the southern portion of the plateau is scoured by the Pecos, Devils, and Nueces rivers as they flow to the Rio Grande. The furthest eastern tip is more heavily marked by rivers, including the Frio, Guadalupe and Pedernales, creating deep valleys. Each of these rivers runs in a meandering path that denotes the area's coastal plain heritage. The northern part has little river activity but does have a number of sinkholes and playas that feed underground solution caves along the Balcones fault line. The limestone shell also contains bountiful oil deposits near Midland and Odessa. This area has now become known as the Permian Basin.
