The Canyon Range, Pavant, Paxton, and Gunnison thrust systems in central Utah form the Sevier fold-and-thrust belt in its type area. The Canyon Range thrust carries an ~12-km-thick succession of Neoproterozoic through Triassic sedimentary rocks and is breached at the surface by the Neogene extensional Sevier Desert detachment fault. The Pavant, Paxton, and Gunnison thrusts carry Lower Cambrian through Cretaceous strata and have major footwall detachments in weak Jurassic rocks. The Canyon Range thrust was active during latest Jurassic-Early Cretaceous time. The Pavant thrust sheet was emplaced in Albian time, formed an internal duplex beneath the Canyon Range during the Cenomanian, and then developed a frontal duplex during the Turonian. The Paxton thrust sheet was initially emplaced during the Santonian, and subsequently formed the Paxton duplex during the early to mid-Campanian. Some slip on the Paxton system was fed into a frontal triangle zone along the Sanpete Valley antiform. The Gunnison thrust system became active in late Campanian time and continued to feed slip into the frontal triangle zone through the early Paleocene. The Canyon Range and main Pavant thrust sheets experienced long-distance eastward transport (totaling >140 km) mainly because they are composed of relatively strong rocks, whereas the eastern thrust sheets accommodated less shortening and formed multiple antiformal duplexes in order to maintain suffi cient taper for continued forward propagation of the fold-and-thrust belt. Total shortening was at least 220 km. Upper crustal thickening of ~16 km produced crust that was >50 km thick and a likely surface elevation >3 km in western Utah. Shortening across the entire Cordilleran retroarc thrust belt at the latitude of central Utah may have exceeded 335 km. The Late Cretaceous paleogeography of the fold-and-thrust belt and foreland basin was similar to the modern central Andean fold-and-thrust belt, with a high-elevation, low-relief hinterland plateau and a rugged topographic front. The frontal part of the Sevier belt was buried by several kilometers of nonmarine and shallowmarine sediments in the wedge-top depozone of the foreland basin system. The Canyon Range thrust sheet dominated sediment supply throughout the history of shortening in the Sevier belt. Westward underthrusting of a several hundred-kilometer-long panel of North American lower crust beneath the Cordilleran magmatic arc is required to balance upper-crustal shortening in the thrust belt, and may be petrogenetically linked to a Late Cretaceous fl are-up of the magmatic arc as preserved in the Sierra Nevada Batholith.

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With up to ∼45 km of slip, the Meade thrust fault in southeastern Idaho is one of the major thrusts in the Sevier thrust belt, yet its age of displacement has remained enigmatic because of the lack of a derivative synorogenic deposit. We propose that the synorogenic conglomerate produced by initial Meade thrusting crops out on Red Mountain, in southeastern Idaho, ∼1.5 km east of the present trace of the Meade thrust. This conglomerate historically has been considered part of the Ephraim Formation of the Lower Cretaceous Gannett Group, but we suggest that it is a conglomeratic facies of the Bechler Formation localized to the area of Red Mountain. Regional stratigraphic considerations and paleontological dates from underlying and overlying strata indicate that the Bechler conglomerate facies (BCF) is Aptian in age. The BCF is 850 m thick and consists of pebble‐ to boulder‐conglomerate, sandstone, and mudrock deposited by fluvial and mass flow processes on medial to distal parts of an alluvial fan. Paleocurrent data indicate an eastward, fan‐shaped dispersal pattern. The BCF contains clasts of micritic limestone, chert‐pebble conglomerate, and cherty litharenite that were derived from the Ephraim Formation. In addition, the conglomerate contains abundant clasts of Ordovician, Carboniferous, and lower Mesozoic rocks that crop out on both the Meade thrust sheet and the Paris thrust sheet ∼25–30 km to the west. The base of the BCF is marked by a local 27° angular unconformity on top of the Ephraim Formation. The BCF contains intraformational, progressively rotated angular unconformities, internal growth folds, and minor dip discontinuities that were produced by simultaneous folding and sediment accumulation on the proximal footwall of the Meade thrust. Provenance modeling indicates that the BCF was derived from Mesozoic strata that were exposed along the frontal part of the Meade thrust sheet and from Paleozoic strata that were coevally exposed in the hindward located Paris thrust sheet. Topography on the Paris sheet was rejuvenated as it was carried passively over a major ramp in the Meade thrust. Provenance and structural data are combined to produce an incremental, bulk‐rock retrodeformation of initial Meade displacement. Clasts of Jurassic Twin Creek Limestone with pressure‐solution cleavage in the lower part of the BCF indicate that an episode of layer‐parallel shortening occurred in the Meade hanging wall prior to Meade displacement; this may have been related to emplacement of the Paris thrust sheet. The BCF recorded ∼6 km of initial Meade‐related shortening by thrust slip and fault‐propagation folding during Aptian time. Illite crystallinity, systematic fracture sets in the Ephraim Formation and BCF, finite strain in Meade footwall and hanging wall rocks, and thermal models by previous workers indicate that the Meade thrust sheet ultimately overrode the BCF and other footwall rocks, probably during Albian‐Cenomanian time. The BCF and the Meade thrust were folded during slip on thrust faults related to the north...

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