Looking at a map of Texas, one notices that its many rivers flow from northwest to southeast, toward the Gulf of Mexico. On closer inspection, a noticeable gap is seen in the south-central part of the State, where few streams are observed between the Colorado River, to the north, and the Pecos River, to the southwest. This is the extent of the Edwards Plateau, a geophysical province that slopes gradually downward from northwest to southeast; elevations at the west end of the plateau exceed 3000 feet while valley floors along its southeast edge are only 300 feet above sea level.
The thin soil of the Plateau overlies a thick deposit of Cretaceous limestone which, in its eastern and southern sections, has been heavily dissected to yield the Texas Hill Country. The northwest edge of the Plateau abuts the High Plains of the Panhandle while, southwest of the Pecos River, the Chihuahuan Desert begins. Along its northern border, bisected by the Colorado River, is the Llano Uplift, where the Cretaceous limestone has been stripped away, leaving outcrops of Precambrian granite and metamorphic rock.
The poor, thin soil of the Edwards Plateau, not ideal for farming, has been used primarily for grazing. Once deposited in a shallow, transcontinental sea, the limestone beds now support rolling grasslands and open woodlands of mesquite, juniper and oak. Marine life has given way to cattle, sheep and goats!
