We outline a method to determine, directly from the data, a subsurface temperature distribution which is compatible with the surface heat flow and takes into consideration the effect of the shallow heat sources. The analysis assumes that (1) the crust is in conductive equilibrium, (2) the lateral changes in thermal conductivity can be neglected, and (3) the depth of the heat sources is proportional to the wavelength of the variations in surface heat flow.We apply the technique to determine the crustal temperatures in two tectonically active regions of the western United States. In the Rio Grande rift, temperatures higher than 1 100 degrees C are predicted at a depth of 20 km. In the transition region between the Colorado Plateau and the Basin and Range, the variability in surface heat flow is partially accounted for by shallow heat sources; however, the increase in heat flow toward the Basin and Range seems associated with deep seated (i.e., lower crust or upper mantle) variations in the thermal regime.

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