Stratigraphy and depositional environments of middle Proterozoic rocks, northern part of the Lemhi Range, Lemhi County, Idaho

Geologic mapping shows Middle Proterozoic strata form two packages of strata north and south of the Tertiary Lem Peak normal fault. Strata north of the fault, the main focus of this report, contain thicknesses and lithofacies of the Big Creek and Apple Creek formations of the Lemhi Group that contrast with those south of the fault. Strata south of the fault, examined mainly in reconnaissance, may have been thrust eastward prior to being downdropped.