Paleoseismology of Utah, Volume 6

The Oquirrh fault zone, Tooele County, Utah: surficial geology and paleoseismicity

Special Study 88, 1996, 64 pages, 2 plates scale 1:24,000, $14.50

ABSTRACT

The Oquirrh fault zone extends discontinuously for 19 miles (31 km) along the northwest margin of the Oquirrh Mountains, Tooele County, north-central Utah. The west-dipping normal fault forms prominent scarps in Quaternary lacustrine and alluvial deposits in the northern and central parts of the fault zone, and a sharp bedrock-alluvial contact in the southern part of the fault zone. Surface faulting offsets some Holocene deposits.

Scarps in the northern part of the Oquirrh fault zone trend generally north-south, and are commonly overlain by latest Pleistocene to Holocene alluvial-fan deposits. Scarps in the central part of the fault zone lie on an elevated spur, the Erda salient, that extends west from the range front and is mostly underlain by deposits of latest Pleistocene Lake Bonneville. The scarp in the southern part of the fault zone borders an indentation in the range, the Pine Canyon reentrant, that is above the Lake Bonneville highstand and generally underlain by Pliocene to Pleistocene alluvial-fan deposits.

Several other buried faults in the vicinity of the Oquirrh fault zone have been mapped in valley fill in previous studies. These faults are postulated on the basis of hydrologic, geophysical, and topographic evidence, but they do not cut surficial deposits. They may be older than, and unrelated to, the Oquirrh fault zone. However, some of them, particularly the Occidental fault, may have been reactivated by later movement on the Oquirrh fault zone.