FEALE.] DESCEIPTIVE GEOLOGY BEAR EIVER AREA. 597 



to tliink tliat there is no faulting, as there is ample room for a fold, and 

 faulting is not common in this immediate neighborhood. The point 

 where I crossed the synclinal, if it exists, was covered with basalt, which 

 effectually concealed the underlying beds. Mr. St. John's report, when 

 published, may throw some additional Ught on the subject. 



BASALT VALLEY. 



As we -come from the Upper Portneuf Valley to the Bear we find the 

 broad valley continuous to the southward as far as the lower end of the 

 Gentile Valley. The portion between the Portneuf and the Bear has 

 been named Basalt Valley for convenience in description. G-eologically 

 it is continuous on the south side of the Bear, Gentile Valley being in 

 reality the lower valley bordering the Bear after it flows out from the 

 Basalt. 



Basalt Valley is about seven miles in width, reaching from the Soda 

 Springs HiUs to the eastern ridges of the southern extension of the 

 Portneuf Eange. As the name implies, it is floored with basalt. The 

 soui'ce of this lava is ]3artly in the Blackfoot region, as we have already 

 indicated, and partly in the craters near the bend of the Bear. In the 

 latter place there are at least two that are very regular in their outline. 

 On one of them Mr. Gannett made a station. It is almost cu-cular, com- 

 posed of a reddish scoriaceous basalt, resembling that of the craters 

 already described on the Blackfoot. linear the craters the basalt is frill 

 of fissures and holes, some of them 50 or 60 feet in depth. The streams 

 that come from the hiUs probably flow beneath the floor, so that the 

 true divide between the Portneuf and the Bear cannot be determined. 

 jSeax the west side of the valley, toward the north, there is one smaU 

 stream that flows on the basalt to the Portneuf. Standing on the west 

 side of the valley the flow of basalt is readily traced to the gap in the Soda 

 Si^rings Hills. The basalt in the Portneuf Canon is a prolongation of this 

 lava stream. At Twin Springs there are remnants of old thermal springs, 

 as at several other localities along the base of the hUls. The most of 

 them are, however, overgrown with grass, which conceals the tufa. 



In the basaltic canon of the Bear, near where it turns to the south- 

 ward, there are calcareous deposits, as seen from the edge of the caQon. 

 The springs are i^robably all cold at present. 



South of this point there is an old crater similar to those seen north 

 of the river. The southern extension of the basalt ends in a tongue, 

 Avhich will be described under the head of Gentile Valley. Almost the 

 whole of Basalt Valley is rough and broken into fissures. There is a 

 rather scanty sup])ly of soil, and yet there is good grass interspersed Avith 

 the sage, so that it would make a tolerably good cattle range, especially 

 as the grass in the neighboring hills is of good quality. On the streams 

 as they emerge from the mountains a small area of arable land may be 

 found, but it is limited to the edge of the hills. Timber on the hills is 

 somewhat sparse. The mass of basalt which can be traced fr'om the Gap 

 in the Soda Springs Hills forms a scarcely perceptible divide in the 

 northern portion of the valley. It appears that the basalt poured 

 through it and then spread to the northward and southward. The 

 northern portion continued on down the caiion of the Portneuf. All the 

 basalt we see in the valley is e^i^dently one flow, but there are several 

 points which seem to indicate that there were at least two flows. One 

 of these points is in the Portneuf Canon and the other in Gentile Val- 

 ley. These two flows were separated by a layer of conglomerate. It 

 therefore appears probable that the first outpouring was into a lake 



