PHYSIOGRAPHY OF BISHOP CONGLOMERATE .621 



were deposited, or the gravels were derived entirely from the part 

 of the mountains north of the river. Further observations will 

 be necessary to determine this point. It is suggested that a study 

 of the relations of the river and gravels in and near the mountains 

 is likely to furnish valuable clues toward the solution of the prob- 

 lem of the history of Green River and its relation to the Uinta 

 Mountain uplift, ^ 



In connection with the evidence of the uplift of the Uintas at 

 or near the close of the Miocene it is a significant fact that the 

 lava-flows of the Leucite Hills were spread out on the surface of 

 this Tertiary peneplain. Earth movements of great magnitude 

 such as those responsible for the uplift of the Uintas are likely to 

 be accompanied by volcanic activity, either in the area of uplift 

 or in neighboring regions. With this fact in mind it would seem 

 more than a coincidence that the Leucite Hills lavas were extruded 

 at about the time of the building of the outwash gravel fans from 

 the newly uplifted Uinta Mountains; since both fans and lava- 

 flows lie on the undissected surface of the peneplain. In this con- 

 nection it is interesting to note that in the Sierra Madre about 

 one hundred miles to the east BalP has found high-level gravels 

 similar to those of the Rock Springs region, in some places overlain 

 by lava-flows. 



Studies in the West^ have shown that the close of the Miocene 

 or more probably the transition period between the Miocene and 

 the Pliocene was a time of extensive mountain uplifts and crustal 

 movements. The Tertiary peneplain of the Colorado valley was, 

 according to Dutton,^ uplifted at this time. Large parts of the 

 Great Basin and the Sierra Nevada and Cascade mountains were 

 elevated. It was at this time that the topographic features of the 

 West began to take shape somewhat as they are today. There 

 occurred over the whole Cordilleras a regional uplift as well as 

 one of individual mountain-ranges. Coincident with these crustal 

 movements were the great lava-extrusions of the late Miocene. 



1 Max W. Ball, "The Eastern Part of the Little Snake River Coal Field, Wyom- 

 ing," U.S.G.S. Bull. 381. 



2 See Chamberlin and Salisbury, Text Book of Geology, III, 274-75, for references. 



3 Button, Monograph II, U.S. Geol. Survey. 



