Geologic setting and origin of the Grouse Creek pluton, Box Elder County, Utah

The southern portion of the Grouse Creek Mountains, located in northwest Utah, consists of about 6000 feet of sedimentary rocks. The stratigraphic column is made up of 1000 feet of Proterozoic phyllites, limestone, dolomite and quartzite; 250 feet of the Ordovician(?) Pogonip(?) formation and 450 feet of the Eureka(?) quartzite; 350 feet of the Devonian Simonson formation and in excess of 1500 feet of the Guilmette limestone; 800 feet of the Mississippian(?) Pennsylvanian(?) Chainman-Diamond Peak(?) formation; 1000 feet of the Pennsylvanian-Permian Strathearn(?) formation; and more than 1000 feet of the Triassic Thaynes(?) formation. Pliocene sedimentary and volcanic rocks of the Salt Lake formation and an apparently local conglomeratic formation mantle the foothills of the range. The sedimentary rocks have the structure of of a major horst composed of flexed sediments broken into numerous fault blocks. Thrust faulting has played a minor role in the evolution of the structure.