446 F. B. WEEKS STRATIGRAPHY OP THE UNITA RANGE 



history. Subsequently, in late Tertiary or Quaternary time, there were 

 minor readjustments. 



Degradation 



Powell in his Geology of the Uinta mountains has discussed the degra- 

 dation of the Uinta range. It seems probable that from the Archean to 

 the close of the Cretaceous, except during Silurian and Devonian time, 

 there was continuous siibsidence and sedimentation in this region. With 

 the inauguration of the continental uplift and the change to fresh-water 

 conditions, sediments were deposited over the uneven floor, filling the 

 hollows and overlapping all the older formations, which continued 

 through Tertiary time and possibly early Quaternary. A thickness of 

 several thousand feet of brackish and fresh-water sediments accumulated, 

 reaching an elevation of 10,000 feet on the northern slope of the Uinta 

 range and 8,500 feet on the southern slope. During Glacial and post- 

 Glacial time to the present erosion has been very rapid. The flanks of 

 the range have been largely denuded of the Tertiary covering. Huge 

 morainal ridges, extending several miles beyond the base of the range and 

 burying large areas of the Tertiary strata, and even the older rocks, are 

 prominent features of the region at the present time. 



Geologic History 



The sediments of pre-Cambrian time in the Uinta range consist of a 

 great thickness of sandstones, and a similar series occurs to the west as 

 far as the Sierra Nevada, extending with some variations from Montana 

 to southern ISTevada. To tlie east the same character of sediments were 

 deposited, but greatly reduced in amount. Beginning with Cambrian 

 time and continuing through the lower Paleozoic, there was great diver- 

 sity in the character and conditions of sedimentation. In the Great 

 Basin province, including the northern and southern Wasatch, there were 

 deposited several thousand feet of shales, sandstones, and limestones in 

 Cambrian and Ordovician time, and in the same region considerable 

 deposits v/ere laid down in Silurian and Devonian time, thinning to the 

 eastward from central JSTevada. In the central Wasatch the Cambrian is 

 thin, but there is a considerable thickness of Cambo-Ordovician sediments 

 Imown as the Ute limestone and Ogden quartzite. In the Uinta region 

 the Cambrian sediments are shales, and a small representative of the 

 Ordovician quartzite occurs. Similar deposits of varying thickness are 

 known to occur in various sections in Colorado and Wyoming extending 

 as far east as the Black hills. Throughout the region extending from the 



