Laramide-style deformation of the Rocky Mountain foreland began in the Lima region of southwest Montana in Coniacian to Santonian (Late Cretaceous) time with the growth of the Blacktail-Snowcrest uplift. The Lima Conglomerate of the BeaverheadGroup locally onlaps its deformed source terrane, the Laramide-style (thick-skin) Snowcrest-Greenhorn thrust-fault system of the foreland, along the southeastern margin of this uplift. Associated sandstones as old as Coniacian to Santonian, also derived from this uplift, are here reinstated into the Beaverhead Group. Northeast of Lima, the Snowcrest thrust transported Archean gneiss, marble, and schist southeastward over deformed Phanerozoic rocks. These Phanerozoic rocks are locally overturned and intensely fractured, and they exhibit many cross-faults. The Archean rocks exhibit locally intense cataclasis, microfaults, and pressure solution at grain boundaries.The first incursion of Sevier-style (thin-skin) thrusting into the Lima region followed Campanian erosion of the Blacktail-Snowcrest uplift, locally to Archean basement. This thrusting shed thick quartzite-roundstone conglomerates eastward. These are placed in a new informal stratigraphic unit, the Little Sheep Creek conglomerate unit, which appears to conformably overlie the fining-upward sequence at the top of the Lima Conglomerate, paiynologically dated as mid-Campanian. Quartzite clasts in the Little Sheep Creek conglomerate unit were probably recycled from proximal fans adjacent to deeply eroded hinterland thrust sheets to the west. However, this unit contains large slide blocks of Mississippian limestone from the front of the closer Four Eyes Canyon sheet, the lower bounding thrust of which reached the land surface, probably in late Campanian time. The Little Sheep Creek conglomerate unit is overridden by the Tendoy thrust. Consequently, the Tendoy is younger than the Four Eyes thrust to the west. Complex structural imbrication of upper Paleozoic and Triassic through Lower Cretaceous rocks of the Tendoy thrust sheet occurs in the Lima Peaks area, above the inferred southwestern extension of the older Snowcrest-Greenhorn thrust system. This imbricate stack, transported east-northeast on the Tendoy thrust, subsequently was folded about a N70°E axis, together with the Tendoy thrust and Lima Conglomerate of its footwall, by possible later reactivation of Snowcrest-Greenhorn thrust system.

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