440 F. B. WEEKS — STRATIGRAPHY OF THE UNITA RANGE 



In the Uinta uplift the Trias, Jura, and Cretaceous strata are largely 

 covered by Tertiary sediments or glacial debris. The principal areas of 

 outcrop are in the Flaming Gorge canyon of the Green river, on the north 

 side of the range, and in the canyons of Green river in the vicinity of 

 Split mountain and Ashley and Dry Forks creeks, and on the Duchesne 

 river several miles below the mouth of West fork, on the south side of the 

 range. The Trias is much thiclcer in the eastern part of the range. In 

 the western part the clayey beds of the upper part of the Trias were ap- 

 parently not deposited. The coarse cross-bedded sandstone, 300 to 400 

 feet thick,- is a dark buff color in the Duchesne region, which varies to 

 lighter color to the eastward. 



JuTa. — The Jura is composed of sandstones, shales, and clay beds, with 

 a prominent limestone series having a maximum thickness of 200 to 300 

 feet, the whole averaging from 600 to 800 feet in thickness, as deter- 

 mined by the 40th Parallel Survey (2, page 200). The Flaming Gorge 

 group of Powell (1, page 152) is considered to represent the Jura. The 

 writer considers the prominent drab limestones to form the base of the 

 series, the remainder of the Jura being formed of the overlying sand- 

 stones, shales, and clays. 



The areas of outcrop of the Jura in the Uinta uplift correspond to 

 those of the Trias and appear to have a greater thickness of beds in the 

 eastern part of the range. In the Duchesne valley the Jura is repre- 

 sented by a compact drab or gray limestone and soft red calcareous shales. 

 The transition from the buff or brown cross-bedded sandstone of the 

 Trias to the Jurassic oolitic and granular limestone is made in less than 

 ten feet of strata. 



Cretaceous. — This system is divided into the Dakota, Colorado, Fox 

 Hills, and Laramie groups, to which are assigned 10,000 feet of sand- 

 stones and clays by the geologists of the 40th Parallel Survey (2, pages 

 200-202). Powell (1, pages 153-161) divides the Cretaceous into the 

 Henrys Fork, Sulphur Creek, Salt Wells, and Point of Eocks groups. 

 The areas of outcrop correspond to those of the Trias and Jura. The 

 writer, not having had opportunity to study these areas, is unable to add 

 materially to previous descriptions. 



Tertiary. — The Tertiary strata of the Uinta and adjacent areas have 

 been described by the 40th Parallel geologists (2, pages 202-325) and 

 divided into the Vermilion Creek, Green Eiver, Bridger, and Uinta groups 

 and the Wyoming conglomerate. Powell (1, pages 161-172) has divided 

 the Tertiary into the Bitter Creek, Lower and Upper Green Eiver, 

 Bridger, and Browns Park groups and Bishop Mountain conglomerate. 

 The Tertiary strata which have been deposited around the Uinta uplift 



