The Pequop Mountains form a tilted cross section through the Mesozoic to early Tertiary crust and display a complex network of Mesozoic metamorphic and contractional features and overprinting Cenozoic extensional structures. Precambrian and Paleozoic miogeoclinal strata and Tertiary volcanic and clastic rocks are exposed within the range. Structurally, these rocks form an east-tilted footwall block bounded on the west by a west-dipping normal fault.

During the Mesozoic the Pequop Mountains occupied a position in the hinterland of the Sevier fold and thrust belt and miogeoclinal strata within the range strikingly display the effects of hinterland shortening and metamorphism. Locally, the Pequop Mountains are situated in, and form the eastern margin of, a terrain of miogeoclinal strata that underwent regional Barrovian metamorphism, which peaked during the Late Cretaceous (Camilleri and Chamberlain, 1997). This terrain includes the Wood Hills and East Humboldt Range–Ruby Mountains to the west (fig. 1). The Pequop Mountains form the lowest grade (non-metamorphosed to lower amphibolite facies), structurally shallowest part of the terrain; ranges to the west expose progressively higher grade and structurally deeper rocks (Camilleri and Chamberlain, 1997; fig. 1). In addition to displaying the effects of Mesozoic metamorphism, the Pequop Mountains also provide a rare, superb cross section through two hinterland thrust faults.

This paper focuses on the description and relative ages of structures, whereas more regional tectonic and structural interpretations of the Pequop Mountains have been presented elsewhere (e.g., Camilleri and Chamberlain, 1997; Camilleri and McGrew, 1997; Camilleri, 1998; Camilleri, 2009). The structure within miogeoclinal strata in the Pequop Mountains is geometrically complex. The most salient structures are a low-angle fault called the Pequop fault and two thrust faults called the Independence and unnamed thrusts (fig. 2). The Pequop fault is the most important structure because it divides Paleozoic strata within the range into two plates that have different structural and metamorphic characteristics. An unmetamorphosed Paleozoic section is present in the hanging wall of the Pequop fault (shown shaded in fig. 2), and a predominantly metamorphosed, ductiley deformed section forms the footwall. Despite the foregoing differences, Paleozoic strata in both the hanging wall and footwall are cut by thrust faults: the Independence thrust in the footwall and the unnamed thrust in the hanging wall (fig. 2).

For simplicity, the structure of the Pequop Mountains is described in four parts. The first part describes structure in the footwall of the Pequop fault; the second, structure of the Pequop fault and its hanging wall; the third, high-angle faults; and fourth, range-bounding normal faults.