Structural and stratigraphic relations in the Wasatch Plateau, the Gunnison Plateau, and the northwestern Cedar Hills suggest a new interpretation of the easternmost limit of thrusting during Late Cretaceous foreland deformation in central Utah. Steep to overturned dips in the Upper Cretaceous Indianola Group within this region are interpreted to reflect involvement of foreland basin clastics in thrust-related structures that deformed the flank of the foreland basin. A subhorizontal overlap assemblage of inferred Paleocene age indicates that the post-thrust erosion surface sloped gently eastward into the foreland basin.
Northeast-striking, southeast-facing homoclines of Indianola Group strata rest disconformably on Jurassic beds. However, favorable horizons within the Arapien Shale of the Jurassic sequence served as a zone of regional decollement, along which younger formations were detached and transported eastward with respect to underlying autochthonous units. The decollement zone was deformed internally by multiple thrusts and by east-vergent isoclinal folds subsequently complicated by local diapiric modifications. Most exposures of the Indianola Group are thus wholly or partly allochthonous. Folds involving Indianola strata apparently include: (1) fully detached ramp anticlines associated with subsurface thrust faults that underlie the southern Wasatch Mountains, Gunnison Plateau, and Sanpete Valley; and (2) partly detached frontal anticlines associated with blmd thrusts that approach the surface beneath the Sanpete VaUey and the western margin of the Wasatch Plateau. Structures inferred locally are consistent with documented patterns of deformation involving foreland elastics elsewhere m the overthrust belt and should influence exploration strategy in central Utah.