120 



GUIDEBOOK OF THE WESTEEX VXITED STATES. 



McCanimoii 



of the Oregon Short Line, the mountains on both sides of the valley 



are composed of Ordoviciau shale, limestone, and 

 quartzite, dipping to the east. A cross section of 

 the valley at this point (fig. 14) shows a fold in the 

 hard rocks which explains how a single formation 



McCammon. 



r 



Elevation 4,763 feet. 

 Poi)ulation321. 



Ogdenlll miles. 



Granger 191 miles. 



moun 



tain ranges. It also slio\\-s the relation of the mountahi wash to the 

 bedi'ock and contams in diagram the record of an interesting series 

 of events. After the mountains were uplifted and had been some- 

 what worn down hv erosion, there seems to have been a long period 



when the earth's crust in this 



ictically 



and the refuse from the wearing down of the mountains on both sides 

 gradually filled the valley to a considerable depth. Subsequently, 



Bannoch 



Rsnge 



Portneuf 

 Range 



Figure 11.— Cross section of Marsh Creek valley at McCammon^ Idaho. 



an elevation of this region gave the streams greater fall, which in- 

 creased their cutting power, so that they gradually washed out deep 

 gullies in the fill. Then came a period of volcanic activity durino^ 

 which great quantities of lava welled up through cracks in the earth's 



volcanoes. The bottom of the valley 



crust 



from 



Marsh 



Arimo to Pocatello, was filled 



came up from a crack along the vaHe}' bottom. After the lava 

 cooled Portneuf River, coming out from' its canron on the east, mav 

 have flowed for a time dircctlj across the top of the lava to the west 

 side of the,vaUey, as suggested by an abandoned channel to be seen 

 along the raihoad just before entering McCammon, and there jomcd 



^^^s^^l^^^itlj it cut a new course along the east edc-e 



Marsh 



tonsrue 



possession of the opposite ledge 



Long after the lava had cooled 



throu 



Pass poured down Marsh Creek vaUey, flowed over the top of the 



CTavel 



ongue 



