GEOLOGICAL SURVEY OF TPIE TERRITORIES. 271 



erate. Ou the upper slopes, west of the broad plain which borders the 

 top of these clitis, there are two other beds of basalt aud one of por- 

 phyritic trachyte, separated by only thin beds of sand and gravel, which 

 reach to the top of the southern hills, about 0,700 feet above tlie sea. 

 The caiion bends northward to the base of the northern mountains, and 

 there winds for some fifteen or twenty miles before opening gradually 

 to the broad plain of the Great Basin of the Snake River. 



As we had descended from the mouth of Salt Eiver, the timber had 

 gradually disappeared from the hills, until we now found only the scat- 

 tered groves of small eottouwoods which mark the hollows where the 

 snow lies late, or mingle with the willows along the banks of the few 

 small streams which escape from the hills into the sage-covered plain. 

 From near the mouth of the caiion, a belt of cedars runs along the course 

 of a high-water bayou on the south side of the river aud forms a con- 

 spicuous feature of the otherwise featureless plain for many miles. 



Some three or four miles below the mouth of this last canon, a small 

 hot spring, 4 or 5 feet across, stands on the north bank of the river, 

 about 20 feet above the bottom. This was not visited by :iuy of our 

 party, but was reported by our guide to be too hot for one to hold his 

 hand in it for more than a half minute. White spring-deposits were 

 seen, from a distance, at several points on the north bank, but there is 

 believed to be no flow at these points at the present time. 



Joining the main party here on the evening of October 8, we passed 

 over the sage-plain described in the record of our outward trip, crossed 

 Willow, Sand, and Blackfoot Creeks, aud reached Fort Hall on tlie 11th, 

 The facts observed during that time, aud during the fjllowing twelve 

 days, while we awaited Dr. Hayden's arrival to pay oft" and discharge 

 the party, have been incorporated in the earlier part of this report. 



