Abstract

Late Cretaceous andesitic volcanic rocks immediately north of the Beartooth Mountain uplift and included in the Livingston formation originated from many small vents near the headwaters of the Deer creeks. The series is composed of volcanic breccias and tuffs near the vents and of volcanic conglomerates and sandstones farther away. The latter are interbedded with Judith River to Lance (upper Cretaceous) sediments. Pipes, dikes, and laccoliths of dacite, andesite, and diorite cut the pyroclastics and near-by sediments. Some breccia beds and the underlying sedimentaiy rocks have been tilted by the intrusion of several laccoliths prior to the Laramide orogeny. Other pyroclastics are later than the laccoliths but pre-Lance. Igneous activity had ceased before the main Beartooth thrusting.

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