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February Bulletin 2023

GEOMORPHIC PROVINCES AND REGIONS OF TEXAS Thomas E. Ewing, Bexar Geological Surveys, San Antonio TXABSTRACTTexas is a state and region with varied landforms, but they have received only limited attention. Reanalysis of geomorphic regions in Texas indicates three major provinces. The Coastal Plains include plains to gentle hilly uplands constructed on poorly consolidated sediments of Late Cretaceous and Cenozoic age that dip gently toward the Gulf of Mexico, containing an important set of escarpments of Oligocene to Late Miocene resistant strata, and bounded (in North Texas) on the west by the White Rock Escarpment. The Interior Plains and Plateaus include three major subgroups: those underlain mainly by limestone and dolomite, mainly of Cretaceous age (the Edwards Plateau, Stockton Dissected Plateau, Balcones Canyonlands dissected plateau, Lampasas 'Cutplain' dissected plateau, and the Grand Prairie and adjoining sandy timbered belts, with the Llano Country an anomalous inlier); those underlain by mainly clastic deposits (with evaporites and carbonates) mainly of Paleozoic and Triassic ages (Palo Pinto cuesta plain, Red Plains, Caprock Escarpment Breaks, Pecos Valley); and two high plateaus underlain by Neogene alluvial and eolian sediment and caliche (Southern High Plains, Cimarron High Plains). The Mountains and Valleys province includes some 20 mountain ranges (of volcanic, tilted fault-block, and complex character), a few plateaus, and a series of broad valleys, either bolsons or drained bolsons, mainly created by Neogene and Quaternary extension. 

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