372 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



of west longitude, or 10° west of the Yellowstone Park. This area is 

 occupied by recent deposits of Pliocene or Pleistocene age and large 



sheets of recent eruptive rocks. The present bed of the Snake river 

 leaves this depression at the eastern boundary of Oregon and flows 

 northward 200 miles (322 km.), cutting a deep gorge in the mountains 

 which lie across its path. There is some reason for assuming that this 

 sudden change of direction is of geologically recent date and that an 

 earlier valley existed further westward. The solution of this question 

 as to earlier draining and as to the age of the recent deposits in this 

 valley, is of ethnological 17 as well as geological interest. 



It will be seen later that the interior basin now occupied by Great 

 Salt lake was once tilled by a much larger lake called Lake Bonneville. 

 At one period in its history Lake Bonneville overflowed and its super 

 lluous water drained out through the Snake River valley. Whether 

 the lavas, which now form the surface of the Snake Plains, were 

 poured out before or after the dessication of this lake has not yet been 

 detinitelv ascertained. 





By 



ITINKKARV. 



S. F. Emmons 



.« 



















Distance. 



Elevation. 



Station. 



Miles. 



Kilo- 

 metres. 



Feet. 



Mil res. 







 25 

 .08 

 28 



„ 



u 



1GG 

 IL' 



4,406 

 4,841 



1 . .'J60 

 1,828 



1,211 







Those who take this excursion leave the Utah Northern train at 

 Pocatello and take the regular train on the Oregon Short Line to 

 Shoshone station, from which they reach the falls by stage. 



At American falls the Snake river is reached. The falls can be 

 seen on the left or below the bridge. A short distance above the 

 bridge, wide, alluvial bottoms border the Snake River, which support 

 a luxuriant growth of grass and large cottonwood trees, where cattle, 

 which pasture on the hills further east, are taken during the winter. 



From American falls downward, the river runs in an ever-deepen- 

 ing gorge in the basalt, whose walls at the bridge are about 70 feet 

 (21m.) high, and at Shoshone falls, about 150 miles (241 km.) lower 

 down the river, are 100 feet (122 m.) and 020 feet (11)0 m.) above and 

 below the falls, respectively. After crossing the river, the railroad 

 keeps a westerly course, slowly diverging from the course of the stream 



From notes furnished by .1. I', [ddinga and J. S. Diller, 



