596 REPORT UNITED STATES GEOLOGICAL SUEVEY. 



water is cold and acid in reaction. The earth and stones surrounding 

 are coated with sulphur. 



The north and east sides of the valley of the Bear, near the springs, 

 are floored with basalt, which does not extend across the river but leaves 

 a broad valley of Quaternary between the river and the mountains. At 

 the bend of the river the valley is only a little over a quarter of a mile in 

 width. The river is on the south side in a canon, the walls of which on 

 the north side are basaltic, with irregular columnar form. On the south 

 are the limestones of the northern end of the Bear Biver Bange. This 

 point, according to Fremont, has been named Sheep Bock. From this 

 gap the Bear passes out into Basalt Valley. 



SODA SPRINGS VALLEY. 



The valley of Soda Spring Creek extends from Bear Biver northward 

 to the plain of the Blackfoot, already described, and, as in the latter, the 

 floor is basalt. The source of the flow is found in the craters near the 

 Blackfoot. The slope of the valley is to the southward. Near the hills 

 walls of basalt are seen, in which an irregular columnar structure was 

 seen. There are numerous fissures and sink-holes, and whatever drain- 

 age there is from the hills, with the exception of Soda Sprhig Creek, 

 sinks beneath the basalt. The Aspen Bidge, which is the eastern 

 boundary of the valley, has been already described. On the west are 

 the Soda Springs hills. 



SODA SPRINGS HILLS. 



North of the bend of the Bear, continuing northwest from the Bear 

 Biver Bange, is a low range of hills. Geologically and topographically 

 this range is divided into two groups by a flow of basalt, which has 

 poured out from the basin of the Blackfoot into Basalt Valley. The 

 southern of these two groups consists of comparatively low ridges. Two 

 stations were made on them. Station 87 is at the north end of the most 

 eastern of the ridges, on limestones, which dip to the northeast. Sta- 

 tion 88 was at the south end, on quartzites. These beds may be Car- 

 boniferous, although it is probable they are Jurassic, as Carboniferous 

 fossils were found on the west side of the hills, in beds some distance 

 below, at the base of the hills, near Twin Springs (see p. 563, chap. IV.) 



The ridge on which these stations are located is about 800 feet above 

 the valley of Soda Spring Creek, and the highest point in the group of 

 hills is only 1,200 feet above the level of Bear Biver at the bend. The 

 dip of the limestones is from 15° to 30°. 



On the west side of the hills there are remains of old hot springs at 

 several places, especially at Twin Springs. The basalt that separates 

 the southern group from the northern seems to form a divide in Basalt 

 Valley between the drainage of the Portneuf and that flowing to the 

 Bear. The latter, however, is for the most part beneath the basalt. 

 The northern group of hills forms the eastern boundary of the Upper 

 Portneuf Valley. The elevation above the valley is only about a thou- 

 sand feet. The summit is flat-topped, so that the general character is 

 somewhat plateau-like. The western part of the hills, as at Station 82, 

 is undoubtedly Carboniferous, with the limestones dipping to the north- 

 east. On Station 70, however, we have Jurassic dipping to the south- 

 west, so that between the two points there must be a synclinal. This 

 would require, therefore, that the eastern portions of the hills be made 

 up of Jurassic strata. The immediate region was not visited, but judg- 

 ing from the outcrops surrounding, this must be the case. .1 am inclined 



