GEOLOGIC MAP OF THE WEST MOUNTAIN QUADRANGLE, UTAH COUNTY, UTAH

A 1:24,000-scale geologic map of the West Mountain quadrangle was completed under the STATEMAP component of the National Cooperative Geologic Mapping Program. This mapping is part of ongoing work by the UGS on the Provo 30' x 60' quadrangle geologic map. The 7.5' quadrangle is located about 15 miles (24 km) southwest of Provo at the south end of Utah Lake and along the Interstate 15 corridor in the northeastern Great Basin. Most of West Mountain consists of Permian and Pennsylvanian marine sedimentary strata capped by probable early Tertiary-Late Cretaceous synorogenic deposits. The southern quarter of the mountain (informally Quarry Hills) consists largely of Mississippian, Devonian, and Cambrian sedimentary strata. We newly subdivided the upper Paleozoic strata (Oquirrh Group and related rocks) using lithologic and fossil data. We also improved mapping of surficial deposits in parts of Utah and Goshen Valleys. These valleys are covered mostly by Quaternary deposits related to the Bonneville lake cycle, as well as by some younger deposits related to Utah Lake and other surficial processes. West Mountain was deformed by Late Cretaceous-early Tertiary contractional folding and faulting of the Sevier orogeny, a subsequent extensional collapse event, and late Tertiary to Holocene Basin and Range extension. We substantially redefined the mountain's geologic structure. A major NE-trending transverse structural zone separates the Quarry Hills from the remainder of West Mountain. Both areas of the mountain were folded into an eastward-overturned anticline and were faulted. The transverse zone, now called the West Mountain fault, was previously mapped as a thrust fault and tear fault; the exact nature of the fault remains unclear. North of the transverse zone the West Mountain thrust places Pennsylvanian over Permian strata along the eastern flank of the mountain, and a low-angle normal fault exists on the southwest flank. South of the transverse zone, the Quarry Hills thrust places Mississippian on Permian strata, and the Quarry thrust is inferred under the north end of Keigley Quarry. Range-bounding normal faults are inferred on the east side (Lincoln Point-Dry Hollow fault) and west side (Bird Island-White Lake fault); these faults may link with faults that reportedly underlie Utah Lake.