The sequence of Paleozoic rocks on the north and west sides of the Uinta Basin ranges in age from Cambrian to Permian. On the west side of the Basin, in the southern part of the Wasatch Mountains, the Paleozoic section is nearly 40,000 feet thick and probably contains the most complete sequence of Carboniferous and Permian rocks in the Rocky Mountain region. This thick section is present only in an overthrust block. North and east of the thrust fault, in the central Wasatch Mountains and the Uinta Mountains is a much thinner section of Paleozoic rocks. The thinner section is only about 8,000 feet thick and apparently large segments of the thick section on the south and west are unrepresented.

Cambrian formations in the Wasatch Mountains include the light brown-weathering Tintic quartzite of Lower Cambrian age, overlain successively by olive-green and brown shale and sandstone and mottled gray limestone of the Lower and Middle Cambrian Maxfield limestone. Locally, the Maxfield is absent at the top of the Cambrian. In the Uinta Mountains, the Cambrian rocks are represented only by a sequence of shale, like that of the Ophir formation with subordinate sandstone. This unit is about 3,000 feet thick near the Duchesne River but decreases in thickness eastward. Fossils from the uppermost beds of the unit near the Duchesne River are of Middle or, more probably, Upper Cambrian age.

A persistent dark gray to nearly white vuggy dolomite 150-265 feet thick in the Wasatch Mountains overlies the Cambrian and is provisionally correlated with the Jefferson dolomite of Devonian age. It may be present in the Uinta Mountains near the Duchesne River, but is not recognized farther east.

The Madison limestone of lower Mississippian age and the Deseret and Humbug formations of upper Mississippian age maintain fairly constant lithologic character along the west and north sides of the Uinta Basin, but the aggregate thickness of the three formations decreases from about 1,800 feet in the Wasatch Mountains to 900 feet or less near Vernal. The dark gray cherty limestone and dolomite of the Madison and Deseret limestones are lithologically similar. Brown-weathering sandstone interbedded with gray cherty limestone characterizes the Humbug formation which commonly shows extensive brecciation. Post-Humbug Mississippian rocks south of the thrust fault in the Wasatch Mountains have an aggregate thickness of about 4,000 feet and include the Great Blue limestone, which consists of lack to dark gray thin-bedded limestone with some dark shale, and the greater part of the overlying Manning Canyon shale which consists of dark shale with some dark limestone and gritty sandstone. North of the thrust fault, the post-Humbug Mississippian is represented in the Wasatch Mountains by about 100 feet of dark shale at the base overlain by 400 to 500 feet of dark gray limestone and along the Uinta Mountains mainly by dark shale 100-300 feet thick. This thin shale and limestone unit is tentatively correlated with the basal part of the Great Blue limestone.

Pennsylvanian and Permian rocks in the southern Wasatch Mountains include the upppermost part of the Manning Canyon shale overlain successively by the Oquirrh, Kirkman, Diamond Creek, and Park City formations. The black shale of the Manning Canyon intergrades with the limestone at the base of the Oquirrh formation. The Oquirrh formation, about 25,000 feet thick, is mainly quartzitic sandstone with some interbedded limestone. Fusulinids of Atoka, Des Moines, Missouri, Virgil, and Wolfcamp age are recognized in the Oquirrh. The gray to black thinly laminated limestone of the overlying Kirkman has a maximum thickness of 1,600 feet, but the formation is absent locally. The Diamond Creek sandstone overlying the Kirkman is a gray to buff calcareous to quartzitic crossbedded sandstone 800-1, 00 feet thick, tentatively correlated with the Coconino sandstone. The Park City formation about 1,800 feet thick, consists of three members: an upper and a lower member of light gray cherty limestone with some sandstone separated by a middle black phosphatic shale member. Fossils suggest at least partial equivalence of the lower member with the Kaibab limestone and the remainder of the formation with the Phosphoria formation. This sequence of Pennsylvanian and Permian rocks with a total thickness of nearly 30,000 feet in the southern Wasatch Mountains, is

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represented on the opposite side of the thrust fault by about 3,000 feet of strata including the Morgan formation at the base overlain by the Weber and Park City formations. The Morgan from 400 to about 1,400 feet thick, consists of a lower limestone unit and an overlying interbedded gray to red limestone and sandstone unit. The Morgan contains fusulinids of Lampasas or Morrow age in the lower part and of Des Moines age in the upper part, thus indicating correlation with the lower part of the Oquirrh formation. The unfossiliferous Weber sandstone, 1,000-1,500 feet thick, in the Uinta Mountains, is correlated with the Pennsylvanian Weber quartzite of the central Wasatch Mountains and tentatively with a lower part of the Oquirrh formation. A stratigraphic break representing a large part of late Pennsylvanian and early Permian time is inferred between the Weber sandstone and the overlying Park City formation. The lower member of the Park City extends a short distance east of the Duchesne River beyond which the middle phosphatic shale member rests on the Weber sandstone. The upper member varies in thickness and apparently intertongues eastward with red and gray beds lithologically inseparable from the overlying rocks of Triassic age.