Temperature data to depths of a few hundred meters were obtained from 29 we& in northeastern Arizona; 12 in the regicm surrounding the San Francisco Volcanic Field, in the Black Mesa area, and 9 in the south-central Colorado Plateau which includes the White Mountains. Although there was evidence for local hydrologic disturbances in many temperature profiles, most wells provided an estimate of the conductive thermal gradient at the site. A few thermal conductivities were measured and were combined with published regional averages for the north-central part of the Colorado Plateau to produce crude estimates of regional heat flux. None of the wells was accessible below the regional aquifers. To these depths, heat flow in the area of the San Francisco Volcanic Field appears to be controlled primarily by regional lateral water movement having a significant downward vertical component of velocity. The mean heat flow of 27 f 5 mWm-2 is only a third to a quarter of what .we would expect in this tectonic setting. The heat that is being carried laterally and downward probably is being discharged a t 1 enthalpy and low elevation in springs and streams of the Colorado Plateau a Mogollon Rim. In the vicinity of Black Mesa, heat-flow averages about 60 mWm-2, characteristic of the "cool interior" of the Colorado Plateau. North of the White Mountain Volcanic Field, the average heat flow is about 95 mWm-2. i 1 1 ' A. The primary aims of this study are: 1) To make the temperature data available to interested workers; 2) to interpret these data to the extent possible in terms of the geology and hydrology of the region, and 3) to suggest some further studies which may help to unravel the complicated interaction between the earth's heat and groundwater in the region.