Bat Cave quadrangle lies on the maturely dissected eastern margin of the Edwards Plateau. Sinkholes, caves, and other karst features are common throughout the uplands. Approximately 1,050 feet of dominantly carbonate rock comprises the ten Cretaceous formations cropping out in the quadrangle. The upper part of the Glen Rose Formation, the Walnut, Kainer, and Person Formations, the Georgetown Limestone, Del Rio Clay, Buda Limestone, Eagle Ford Shale, Austin Limestone, and Taylor Clay are exposed. The oldest and youngest rocks crop out in the northwestern and southeastern corners, respectively. Five major, downthrown to the coast, high angle, normal faults of the Balcones fault system pass through the quadrangle. Together with 86 minor antithetic, synthetic, and cross faults, they produce 1,200 feet of stratigraphic displacement from northwest to southeast. Major faults trend between N. 40° E. and N. 60° E. Minor faults have more variable orientations, but tend to strike either east-west or N. 40° E. to N. 60° E. The Upper Member of the Glen Rose Formation supplies small amounts of fair to poor quality water to wells in the northern half of the quadrangle. The Kainer and Person Formations, which yield large amounts of good quality calcium bicarbonate water, are the principal aquifers in the southern half. / text