122 GUIDEBOOK OF THE WESTEEX UXITED STATES. 



tinuous on the west side of tlie track. Areas a few yaixls in extent 

 showing radiate columnar structure may be seen at several points 

 close to the railroad between McCammon and Pocatello. 



Onyx is a siding just below a concrete bridge over Portneuf River. 

 Near milepost 200 ^ the river tumbles over falls made by travertine, 



a soft cellular limestone deposited from calcareous 

 ^^y^' spring waters. The small knobs of limestone in the 



Elevation 4,615 feet, valley bottom bctwccn the 198 and 200 mile posts 



Ogden 117 miles. i'1'-it i-i t it 



Granger 197 miles. ^vcrc oncc buried m the lava which spread over the 



whole valley floor but have been brought to light 

 again through the wearing away of the lava by the river. 



Near the 201-mile post the railroad and river turn to the middle of 

 the larger valley^ where there are basalt walls on both sides. An 

 abandoned channel of Portneuf River continues along the east edge 

 of the lava mass, so that the lava east of Inkom is an isolated block 

 lying between the abandoned channel and the new channel of Port- 

 neuf River. 



At Inkom^ a small settlement just below the point where Marsh 

 Creek enters Portneuf River, the river turns from north to west and 



cuts through the range in a deep, narrow valley. The 

 basalt formerly occupying the present position of 



Elevation 4 520 feet j. */ o r r 



Popuiation549. Inkom has been gradually removed by the stream 



Ogden 122 miles. which comcs in from the northeast. Portneuf River 



has worn the basaltic lava away from the south side 

 of the valley from Inkom to Pocatello, leavmg a black columnar wall 

 on the north side of the track. In some places it is very apparent 

 that there are two thin sheets of lava, one resting upon the other, 

 indicating two distinct volcanic outbursts. About 4 miles west of 



Inkom, 



Inkom the lava stops short, and there is none in the narrow pass 



through the mountains. 



' The valley of Portneuf River from McCammon to Pocatello is cut 

 in ancient Paleozoic rocks, including limestones, shales, and quartz- 

 ites, tilted at various angles but for the most part to the east. The 

 Bannock Range west of Inkom, through which the train passes so 

 quickly, is composed of Ordovician strata which are more or less 

 folded, an antichne or upward bend being indistinctly recognizable 

 on the south wall of the pass. There is no picturesque canyon here — 

 only a short, sharp gap. A great fault or break in the rocks along the 

 west side of the range crosses the river at the west end of this gap, but 

 no trace of it can be seen from the train. 



in uie x^onneui \ aaey between McCamni' 

 indicate the distance west of Granger, Wyo. 



