New heat flow data in Arizona suggest that the southern Basin and Range has recently undergone less extension than other areas of the Basin and Range province. Heat flow–heat production data imply that magmatism and hydrothermal circulation in the crust and upper mantle beneath southern Arizona and northwestern Mexico may be less extensive than along the Rio Grande rift. A heat flow transition between the Basin and Range and the Colorado Plateau occurs within a lateral distance of 60 km in central Arizona. Predicted steady state temperatures suggest that the M discontinuity may be nearly coincident with an isotherm along this transition. The new heat flow measurements from depths greater than 650 m suggest that the mean value for the Arizona Basin and Range is 1.94 ± 0.12 HFU, indicating as little as 0.3 to 0.4 HFU difference between the Colorado Plateau and the Arizona Basin and Range. This difference could be attributed primarily to widespread magmatic intrusion in the Basin and Range.

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Fifteen heat‐flow measurements are presented for eastern Arizona and neighboring areas. In the Gila Mountains of southeastern Arizona a heat flow of 1.9 HFU (the approximate average for the Basin and Range Province) is estimated from the best measurements. In the eastern part of the Saffobrd Valley, just south of the Gila Mountains, subsurface temperature gradients were measured at one site to 1050 m. Heat‐flow data from this site, considered with the reported hydrogeology and hot spring activity of the valley fill deposits, suggest complex hydrothermal phenomena in the valley. Several hundred km to the north, high heat flows (≥2.5 HFU) are observed within the Mogollon Slope of the Colorado Plateau. These high heat flows, about 100 km from the southern boundary of the Colorado Plateau, are believed to result from the sources of extensive Quaternary volcanics in the region. Still farther into the interior of the Colorado Plateau the Black Mesa Basin has an estimated heat flow of 1.5–1.8 HFU and a uniform geothermal character (1 HFU = 41.8 mW/m2).

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