202 DESCEIPTIVE GEOLOGY. 



of the strata involved. Between the Yampa Plateau and the main fold, in 

 the synclinal trough of the Yampa Valley, is a remnant of the Triassic beds, 

 which has escaped erosion, while the western end of the valley is walled 

 in by a faulted-up mass of Palaeozoic strata, which separates it from the 

 synclinal valley of Brush Creek. 



Beyond the limits of the range to the eastward, the contracting forces 

 produced two minor corrugations, which are represented by the anticlinal 

 folds of Junction and Yampa Peaks, and, between these and the Archaean 

 body of the Park Range, an irregular series of broad, gentle undulations. 

 To the north of the Archaean body of Red Creek was also some disturbance 

 of the conformable series of beds, resulting in a broad quaquaversal fold 

 in the vicinity of Bitter Creek, and, on the western edge of the basin, a 

 series of narrow, wave-like ridges were formed, having a direction resultant 

 of that of the shores of the Uinta and Wahsatch Mountains, whose influ- 

 ences in the folding are seen in the two independent directions of strike 

 found in these ridges. 



Tertiary Formations. — The movements of this period of Cretaceous 

 upheaval, which involved also the Colorado Range, and a second uplift in 

 the Wahsatch Range, resulted in the cutting off from the ocean of a great 

 area, of which the Tertiary basins represented in the map formed part, and 

 which was afterward filled by fresh-water seas. At the close of the period 

 of upheaval, the highest crest of the Uinta Range must have stood about 

 30,000 feet above the bottoms of the surrounding basins; but this differ- 

 ence of level, by the abrasion of the rocks which formed the crests of folds, 

 and the consequent filling up of the basins by the sediments resulting 

 therefrom, has been reduced at present to about 7,000 feet. The great 

 erosion, which took place previous to and during Tertiary times, was prin- 

 cipally a gradual wearing away and planing off of the crests of the folds, 

 of whose ]-esultant forms little trace is seen in the present topography. The 

 only well-defined relic of pre-Glacial erosion is seen in the deep axial valley 

 of Brown's Park, whose general form, except for the filling in and levelling 

 off of its bottom, must have been very much what it now is, in early Ter- 

 tiary times. The principal deposition of strata in the Green River Basin 

 took place during Eocene times; those of later times, of which the evidences 



