The Texas Hill Country is a region of central Texas, USA, that features rolling, somewhat rugged, hills that consist primarily of limestone. The region is the eastern portion of the Edwards Plateau bounded by the Balcones Fault on the east and the Llano Uplift to the west and north. The terrain is punctuated by a large number of limestone rocks and boulders and a thin layer of topsoil whick makes the region prone to flash flooding.
Several cities, including Austin, San Marcos and New Braunfels were sited in the flat areas immediately to east of the Balcones Fault line where rivers flow across it, ostensibly because of their natural beauty and the natural wind break formed by the hills.
Due to its karst topography, the area also features a large number of caves, such as Inner Space Caverns and Natural Bridge Caverns. The deeper caverns of the area form several aquifers which serve as a source of drinking water for the residents of the area.
It is largely drained by tributaries of the Colorado River, including the Llano and Pedernales rivers, which cross the region west to east and join the Colorado as it cuts across the region to the southeast, emerging from the hills west of Austin.
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