Browsing by Subject "Geology--Texas--Comal County"

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Geology of Bat Cave quadrangle, Comal and Bexar Counties, Texas
(1971-08) Newcomb, John Hartnell, 1946-; Young, Keith, 1918-2004
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.
Geology of the Wimberley area, Hays and Comal Counties, Texas
(1970-01) Grimshaw, Thomas Walter, 1945-; Young, Keith, 1918-2004
Cretaceous limestone, marl, and dolomite of Late Aptian to Middle Albian age crop out in the Wimberley area, a 5-minute by 10-minute quadrangle in central Texas situated in the dissected eastern margin of the Edwards Plateau. Formations exposed are the upper part of the Glen Rose, the Walnut, and the lower part of the Edwards. The Glen Rose, which crops out over 90% of the area, is subdivided into 7 informal members defined on mappability on aerial photographs. Six major step faults of the Balcones fault zone transect the area, displacing the strata downward to the southeast about 700 feet. The outstanding geomorphic features are the high relief hills and ridges south of the Blanco River, which are caused by dissection along the Edwards Plateau margin, and the deflections of Cypress Creek and Blanco River where they cross faults.
Geology of Waco Springs Quadrangle, Comal County, Texas
(1957-08) Bills, Terry Vance, 1930-; Young, Keith, 1918-2004
Youthful karst topography and entrenched drainage are two conspicuous geomorphic aids in interpreting the geologic history of the Waco Springs quadrangle. Three high angle, dip slip strike faults of the Balcones system, displaced toward the coast, have off-set all, and exposed most, of the southeastward dipping Comanchean and Gulfian rocks. Broad shallow anticlines are created by a "reversal of dip" on each downthrown fault block. Waco Springs, located in the southwestern part of the map area, has a separate groundwater reservoir from the remainder of the quadrangle, and its discharge is dependent on rainfall concentrated in central Comal County.