PHYSIOGRAPHY OF BISHOP CONGLOMERATE 631 



SUMMARY 



The succession of events indicated by this study is as follows: 



1 . Planation, in progress during the latter part of the Tertiary, 

 reduced the Rock Springs region, including all the area from the 

 Uinta Mountains to the northern end of the Leucite Hills, to the 

 condition of a peneplain of very even surface surmounted by a few 

 small monadnocks of especially resistant rocks. This peneplain is 

 possibly to be correlated with that of the high plateau country to 

 the south in Utah and Arizona. 



2. Mountain-building. — Pronounced orogenic movements in the 

 late Miocene or early Pliocene brought the foregoing period of 

 planation to a close. These movements resulted in a very con- 

 siderable renewed uplift along the Uinta mountain-range and a 

 general elevation of the whole region. A change to a more arid 

 climate than formerly is also indicated. Extensive waste slopes or 

 desert alluvial fans were developed round the base of the mountains, 

 and spread far out over the adjacent plains. A remnant of this 

 desert-fan deposit forms the Bishop Conglomerate described in 

 this paper. 



3. Erosion. — A long period of erosion, probably with a moder- 

 ately moist climate and relatively steep stream-grades, gave rise 

 to the present diverse topography. Subsequent to the deposition 

 of the gravels, erosion or faulting reduced the height of the Uintas 

 so much that parts of the mountains which must have supplied the 

 gravels now lie at levels lower than the tops of the gravel-beds 

 fifteen to twenty miles away. 



4. Aggradation. — A change to arid climate brought about a 

 cessation of erosion and a change to conditions of aggradation. 

 The stream-valleys were silted up, and extensive wash-aprons 

 developed at the base of the steeper slopes. 



5. Erosion. — A return to moister climate resulted in the partial 

 dissection of these wash-aprons and valley-gravels, producing 

 terraces along the valley-sides. 



6. Aggradation. — Another change to aridity resulted in the 

 formation of the "valley-iiU" of the present streams. Some 

 smaller stream- valleys with steep side slopes were partially choked 

 and the stream-grade destroyed by desert fans. 



