208 STRUCTURAL GEOLOGY. 



east, but as often we find escarpments facing the northeast composed of 

 beds of the Brown's Park period, horizontal or gently dipping to the south- 

 west, i. e., the escarpments of this range are sometimes reversed, because of 

 the reverse movement along the planes of fracture or the zone of flexure. 



BROWN'S PARK. 



In this discussion I shall not only include Brown's Park proper, but a 

 district of country stretching to the southwest, between the Dry Mountains 

 and Escalante Peaks to the Snake River. Here we have a geological basin 

 with a floor of Uinta Sandstone and Carboniferous and Mesozoic rocks. Its 

 longest diameter is in the same direction as the axis of the Uinta uplift, and 

 while the basin extends somewhat southward across the axis, yet the larger 

 part of the basin is on the north side of the axis. But the old lake basin 

 extended eastward and northward far beyond the area included in the Uinta 

 uplift and beyond the present channel of the Snake River, and here the floor 

 is unknown ; but this latter region is not within the limits of present discussion. 



Within the region under discussion on the floor of the old lake basin 

 beds of the Brown's Park period were deposited; these beds lie chiefly in a 

 horizontal position, but on the north side of Brown's Park the beds are 

 abruptly turned up against the Uinta Sandstone of the O-wi-yu-kuts Plateau, 

 with a dip of about twenty-five degrees. Farther to the east, near the divide 

 between the waters of the Green and the Snake, south of the monoclinal 

 flexure and fault of the Dry Mountains, a deep synclinal flexure is observed; 

 parallel with it and still farther south another of less magnitude, and still 

 beyond a third but slightly developed. 



Let us now consider the effect which the reverse throw along the great 

 Uinta fault and the throw along the Yampa fault has had on this valley. 

 In the former the downthrow at Red Creek is perhaps less than 1,000 feet; 

 at Diamond Peak, about 3,000 feet; and the total throw of the two displace- 

 ments in the Dry Mountains and vicinity is probably more than 4,000 feet. 

 The throw of the Yampa fault, from its inception on the west, soon attains 

 a magnitude of 5,000 feet, and where it is lost by transverse structure, near 

 Junction Mountain, it is about 3,000 feet. Thus it is seen that the great 

 block between these two faults lias fallen down from 1,000 to 5,000 feet in 



