Abstract

Several localities in northwestern Utah and southern Idaho contain evidence for Mesozoic deformation in the hinterland of the Sevier orogenic belt, including: the Albion Mountains, Black Pine Mountains, Newfoundland Mountains, Pilot Range, Crater Island, and Gold Hill, as well as several areas in northeastern Nevada. Although definitive age constraints are lacking to the east (between 112° and 113° W), deformation in northern Utah and southern Idaho is interpreted as probably Mesozoic in age based on structural style and correlation with features farther west. The Hansel allochthon, a regional structural unit, is considered here to have been displaced by about 15 km or more by west-to-east thrusting prior to the Late Cretaceous. This survey of the geographic distribution and style of Mesozoic hinterland deformation suggests that: (1) The Mesozoic structural history of the hinterland, at least as far east as the west side of the Great Salt Lake, began prior to the latest Jurassic (150 m.y.), but probably during or after the Early Jurassic and that it was probably contemporaneous with the Nevadan orogeny; (2) the oldest deformation is characterized by bedding parallel, horizontal or subhorizontal shortening; (3) horizontal extension also locally characterized the Mesozoic hinterland; and (4) the structural style of the hinterland is considerably different than that of the overthrust belt farther east.