6 5 8 



THE PLEISTOCENE PERIOD 



various stages of the lake's history, and even since Lake Bonne- 

 ville disappeared. Since this time, too, there has been faulting in 

 the basin, with displacements of as much as 40 feet (Figs. 538 and 

 541). Furthermore, the shore lines of the former lake have been 

 warped so that some parts are more than 300 feet higher than others 

 (Fig. 538). 



Farther west, but still in the area of the Great Basin, were other 

 lakes, probably contemporaneous with Bonneville. Among them 



Fig- 539- Shore of former Lake Bonneville, Wellsville, Utah. (U. S. Geol. Surv.) 



Lake Lahontan l was of importance. Its history and that of a lake 

 which occupied a part of Mono Valley, California, were similar to 

 that of Lake Bonneville. 



Glacial effects. The extent of glaciation in the western moun- 

 tains was outlined in the early part of this chapter. The erosive 

 work of the mountain glaciers was considerable, as shown both 

 by the extensive deposits of glacial drift, and by the forms of the 

 valleys which the glaciers occupied. The most massive accumula- 

 tions of drift are in the form of lateral moraines, which in some 

 cases are nearly or quite 1,000 feet high. Under the conditions of 

 active drainage which existed in the mountains, much of the glacial 



1 Russell, Mono. XI, U. S. Geol. Surv. 



