Twelve new heat flow values in Wyoming are in the range 0.6–2.1 μcal/cm2s (25–88 mW/m2). Radioactive heat productions at eight localities range from ∼0 to ∼1.3 μμcal/cm3s (∼0−5.4 μW/m3). These data are consistent with the following interpretations: (1) The Laramie Mountains‐eastern Wyoming Basin area is a zone of normal heat flow (0.6–1.6 μcal/cm2s (25–67 mW/m2)) that is characterized by low flux (∼0.6 μcal/cm2s (∼25 mW/m2)) from the lower crust and upper mantle. (2) The eastern boundary of the Yellowstone caldera heat flow high (≥2.5 μcal/cm2s (≥105 mW/m2)) is narrow. (3) The heat flow is high (1.9–2.1 μcal/cm2s (79–88 mW/m2)) in parts of the Black Hills in northeastern Wyoming and western South Dakota. From the data presented, a major heat flow transition occurs between the Medicine Bow and Laramie mountains in Wyoming (0.6–1.3 μcal/cm2s (25–54 mW/m2)) and the Rocky Mountains in northern Colorado (2.2–3.0 μcal/cm2s (92–125 mW/m2)). The high flux in this part of the Southern Rockies may mean that the zone of high heat flow associated with the Rio Grande rift extends to the Colorado‐Wyoming Border. The normal heat flow in the Laramie Mountains‐eastern Wyoming Basin area implies submelting temperatures in the upper mantle. In contrast, the very high flux in northern Colorado may be related to high‐temperature, nonradiogenic heat sources in the lower crust and upper mantle because the width of the transition to normal flux in the Lar