ESTIMATES OF OFFSET OF QUATERNARY ALLUVIAL FAN SURFACES ALONG NORMAL FAULTS BOUNDING THE CENTRAL AND NORTHERN GRANT RANGE AND RAILROAD VALLEY IN EAST-CENTRAL NEVADA

The central and northern Grant Range is bounded on the west by a west-dipping normal fault system that cuts a series of older Quaternary alluvial fan surfaces but predates the development of modern alluvial fans. This fault system contains four general segments. From north to south they are the Box, Heath, Grant, and Irwin canyon segments. The northern and southernmost segments are the longest (> 8 km) whereas the central Heath and Grant canyon segments are the shortest (~ 3-5 km). We constructed topographic profiles to obtain preliminary estimates of net vertical surface offset for each fault segment. The data overall indicate that the longer northern- and southernmost fault segments have the greatest surface offsets with vertical displacements ranging from 9 to 6 meters in the northern Irwin Canyon segment and 21 to 6 meters in the southern Box Canyon segment. The shorter, central segments have lower overall surface offsets with vertical displacements of ~ 5 meters in the Heath Canyon segment and ~ 2 meters in the Grant Canyon segment. Crosscutting relationships indicate that offset on the southern Irwin Canyon segment predates offset on the central Grant and Heath Canyon segments indicating that the offsets of alluvial fan surfaces in the Grant Range were not all produced from the same slip event.