NEW GEOLOGIC MAPPING OF THE GOOSEBERRY CREEK 7.5' QUADRANGLE, CENTRAL UTAH

The Utah Geological Survey completed a new 1:24,000-scale geologic map of the Gooseberry Creek 7.5' quadrangle in the northwest corner of the Fish Lake Plateau in central Utah. This mapping, which is funded through the STATEMAP component of the National Cooperative Geologic Mapping Program, will produce a printed map and a GIS dataset, and will be incorporated into an ongoing project to map the Salina 30'x60' quadrangle.

Strata exposed in this quadrangle range from Late Cretaceous (Campanian) to late Eocene in age (deposits ranging from 77 to 40 million years ago), and includes the Blackhawk, Castlegate, Price River, North Horn, Flagstaff, Colton, Green River, and Crazy Hollow Formations. Two Oligocene to Miocene? welded tuffs, a latite and a trachyte, have a source to the south, and extend into the southern end of the quadrangle.

The quadrangle lies at the southern end of the Wasatch monocline, and the rocks on the west side dip to the west. Several parallel faults step down to the east into the Water Hollow graben, which is bounded on the east by a large down- to- the- west fault. These faults have up to 300 m displacement.

Previous mapping of the Gooseberry Creek quadrangle done in the 1960s-70s was on planametric bases, simplistic, and focused on the volcanic rocks to the south. Improvements from this project include detailed mapping of surficial deposits, faults, contacts, and members, and accurate placement on a modern topographic base. We also mapped several new members of formations, documenting complex facies changes and thinning of strata deposited on the southern flank of a developing Paleogene basin.