A preliminary heat flow map of west Texas
— Bruce Taylor and Robert F. Roy

Western Trans-Pecos Texas lies at the boundary of the Basin and Range and Great Plains, and should therefore reflect the heat flow characteristics of both tectonic provinces. Although few in number, previous heat flow measurements in the region are largely consistent with this assertion. Herrin and Clark (1956) determined the heat flow in the Permian Basin oilfields to be 1.1 H.F.U. (1 H.F.U.=10^-6 cal/cm²/s=41.8 mw/m²), typical of the stable midcontinent area. Three values published by Decker and Smithson (1975) indicated the possible location of the Basin and Range boundary in the westernmost counties of Trans-Pecos, and suggested a near "normal" heat flow in the south of the area, despite the presence of an extensive Tertiary igneous field. Two further measurements (Swanberg and Herrin, 1976; Smith and Jones, 1978) in the Big Bend area again indicate a heat flow only a little above that of the Great Plains, perhaps indicating a transition zone.

Heat flow data in southern New Mexico are more abundant, and a thermal anomaly associated with the Rio Grande rift is now well established (Reiter and others, 1975; Decker and Smithson, 1975; Swanberg and Morgan, 1978), distinguishable above the "normal" heat flow for the Basin and Range (about 2 H.F.U.). Much current speculation concerns the continuation (or otherwise) of the rift into northern Mexico and West Texas.