POST-CRETACEOUS HISTORY OF WESTERN WYOMING 333 



out upon plateau surfaces at least twenty-five miles from the 

 mountains. 



Summary of glaciation: From this discussion a few generali- 

 zations arise. All of the principal ranges of the district, except 

 perhaps the Owl Creek Mountains, were glaciated during the 

 Quaternary period. There were certainly two stages of glaciation 

 separated by a long period of time, and the later of these can again 

 be resolved with some confidence into two. A few facts slightly 

 suggestive of a fourth epoch, still older than the others, are quite 

 inconclusive. The glaciers of the Pinedale and Bull Lake stages 

 were ordinary valley glaciers, which ran but little beyond the 

 mountain fronts and rarely deployed outside their individual can- 

 yons. In most valleys, the younger of these glaciers were shorter 

 than the older, although in a few instances they were not. In the 

 Buffalo stage, however, a large piedmont glacier spread westward 

 from the north end of the Teton Range, and Yellowstone Park 

 appears to have been almost entirely buried under a mass of ice. 



There is much resemblance between the sequence of glacial 

 events in this district and that described by Atwood in the San 

 Juan Mountains of Colorado. Although full confidence should not 

 be placed in a long-distance correlation made without indulging in 

 a more detailed and comprehensive study of the Rocky Mountains, 

 it may be suggested that the deposits characteristic of Atwood's 

 "Uinta," "Bighorn," and "San Juan" stages correspond in many 

 respects to those of the Pinedale, Bull Lake, and Buffalo stages in 

 western Wyoming. The Pinedale and "Uinta" moraines are alike 

 in being very fresh and almost uneroded. The Bull Lake moraines 

 resemble somewhat those of Atwood's "Bighorn" stage in being 

 notably eroded although still traceable, but the Bull Lake moraines 

 are rather better preserved. Like the till of Atwood's "San Juan" 

 stage, the Buffalo moraines have been intrenched 500-1,000 feet 

 and so reduced in area that at best their original forms can be but 

 rudely traced, and in some places they constitute mere remnants 

 which suggest nothing of former distribution or derivation. 



Work of gravity with the aid of weathering. — Here, as in all regions 

 of sharp relief, the steeper slopes are wasting away under the 

 attacks of the weather; and the resulting debris has been making 



