San Antonio and Austin lie on the boundary between two distinct geographical regions of Texas: the coastal prairies and the Hill Country. The coastal prairies extend from the Gulf Coast all the way into Central Texas. They are mostly flat, with gentle undulations as they stretch inland. In the descriptions of early settlers, this prairie land was metaphorically described as a sea of grass, for its vastness, uniformity, and lack of natural features. When the wind would blow, the metaphor was even more striking, as the tall grass would bend to and fro in waves that rolled across the landscape.
The Hill Country is situated on a large limestone shelf that has been pushed up over 1,000 feet by volcanic uplifting. The entire raised area is known as the Edwards Plateau. And it is the eastern side of this plateau that is labeled the Texas Hill Country, where the warping of the earth's crust produced the hilly terrain.
The boundary between the coastal prairie and Hill Country is the Balcones Fault, which crosses central Texas in a diagonal line from southwest to northeast, roughly paralleling the interstate highway I-35. In this fault zone the limestone shelf is fractured, and the water pouring off the plateau on its way to the Gulf seeps into the fissures and returns to the surface in the form of natural springs, which are abundant in this region. Water coursing through the limestone has also carved out caverns and formed stalactites and other mineral formations. Most of these caverns are not far from the interstate highway, and can make for enjoyable breaks from driving.
The higher altitude of the Hill Country makes for slightly milder, less humid summer weather. Whereas San Antonio and Austin are roughly 600 feet above sea level, Kerrville and Fredericksburg, the two largest towns of the Hill Country, are at an altitude of more than 1,700 feet The soil is generally thin and more appropriate for ranching than farming, but certain areas, especially the land around the German farming community of Fredericksburg, are rich enough to sustain intensive agriculture. Indeed, Fredericksburg peaches, harvested from May to July, are famous in Texas for their quality. But the real agricultural boom these days is in grapes for winemaking. Several vineyards are now well established in the Hill Country, and their number increases annually.
Frederick Law Olmsted’s description in his 1853 A Journey Through Texas is poetic. San Antonio, he writes, “lies basking on the edge of a vast plain, through which the river winds slowly off beyond where the eye can reach. To the east are gentle slopes toward it; to the north a long gradual sweep upward to the mountain country, which comes down within 5 or 6 miles; to the south and west, the open prairies, extending almost level to the coast, a hundred and fifty miles away.”
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