Twelve new heat flow values in Wyoming are in the range 0.6--2.1 μcal/cm2 s (25--88 mW/m2). Radioactive heat productions at eight localities range from ~0 to ~1.3 μμcal/cm3 s (~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/cm2 s (25--67 mW/m2) that is characterized by low flux (~0.6 μcal/cm2 s (~25 mW/m2) from the lower crust and upper mantle. (2) The eastern boundary of the Yellowstone caldera heat flow high (?2.5 μcal/cm2 s (?105 mW/m2)) is narrow. (3) The heat flow is high (1.9--2.1 μcal/cm2 s (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/cm2 s (25Pxn54 mW/m2)) and the Rocky Mountains in northern Colorado (2.2--3.0 μcal/cm2 s (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 hgih 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 Laramie Mountains in southern Wyoming is narrow (?70 km).