Blind thrusts of the Lima System beneath the Lima Anticline and the Tendoy thrust sheet to the west. Rocks of the exposed Tendoy Sheet have never been deeply buried, based on vitrinite reflectance of < or =0.6%, conodont (color alteration index) values that are uniformly 1, and on supporting organic geochemical data from Paleozoic rocks. The Laramide Blacktail-Snowcrest uplift east of the frontal thrust belt is asymmetric. Uniform conodont CAI values of 1 from the Blacktail-Snowcrest uplift indicate that no thick cover of Upper Cretaceous or younger rocks extended over the flanks of the uplift. Potential petroleum source beds and reservoir rocks are both present in Southwest Montana. However, remnants of Tetiary lava flows, basin-and-range faulting, and supermaturity with respect to oil of Permian and older rocks in the western Centennial uplift area are additional factors which must be considered.--Modified journal abstract.