|Geologic age||Pliocene to Pleistocene|
Unconsolidated > Coarse-detrital > Gravel (Bed)
|Comments||Caliche-cemeneted gravel; some boulders up to 1 ft diameter; well-rounded cobbles of chert, some cobbles of quartz, limestone, and igneous rock; present on topographic divides and high areas not associated with present drainage; extensive deposits in Medina and Uvalde Cos. Thickness from several feet of gravel lag to about 30 ft. According to Moore and Wermund (1993): Alluvial sandy gravel--pale-brn, lt.-yell-brown, and reffish-brn sandy gravel and gravelly sand containing small proportions of silt and clay. Typically cemented by secondary calcium carbonate, ranging from hard calcrete that will not slake in water to soft calcareous zones; depth of cemented zone 0.2-2 m. Abdt, well-rounded pebbles and cobbles of chert, quartz, and limestone; minor igneous rock; some boulders. Caps drainage divides, upland flats, and rounded ridges 30-75 m above streams. Extensive upland depodist on high alluvial terraces along Rio Grande and in northern Nueces Plains. Thickness 1-6 m.|
Bureau of Economic Geology, 1977, Del Rio Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1976, Crystal City-Eagle Pass Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1974, San Antonio Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000.
|Counties||Atascosa - Bexar - Dimmit - Frio - Kinney - La Salle - Live Oak - McMullen - Maverick - Medina - Starr - Terrell - Uvalde - Val Verde - Webb - Zapata - Zavala|