THE OYEKLAXD ROUTE COUNCIL BLL^FFS TO OGDEX. 



79 



Just west of Spring Valley station the train crosses a small expo- 



Frontier formation.^ Tliese coal-bearing rocks are of 

 Upper Cretaceous age and have been exposed be- 

 cause of the removal of the red beds of the Wasatch 

 *^- group that once covered them. Several abandoned 

 prospects and old coal mines may be seen on eacli 

 side of the track, but no coal is mined here now. 



Aspen is a small station at the east end of the Aspen tuimoL From 



Spring Valley. 



Elevation 7,003 fe 

 Omaha 905 miles. 



Creek 



Aspen* 



Elevation 7,175 feet. 

 Omaha 909 miles. 



going thi'oug 



the head of one of its tributaries. In 



r 



the tunnel the train passes from the area drained by 

 Colorado River to the Great Basin — that portion of 



Am 



sea. 



fhid 



Creek and Black Fork to Green River and thence throng 



Gulf 



Those west of 



this ridge find their way to Bear River and flow by a circuitous 



evaporation. 



onlv bv 



tunnel 



Wasatch group, but the Oyster Ridge sandstone m 



ni 



Tces 



HiUi 



age, next ^^ounger than the Frontier.' 



West of Altamont the route passes for about 2 niiles through an 

 open valley occupied by the soft HiUiard shale, then crosses the fault 



Altamont. 



Elevation 7,217 feet. 

 Omaha 911 milfts. 



line that separates this sh 

 mation,^ the oldest format 



om 



Wvoming^ 



na^ro^v 



carved 



sandstone of that formation 



This sandstone, upturned to a 

 >s out in sharp ridges composed of 



^ The Frontier formation consists of 

 coal-bearing sandstone and shale of Ben- 

 ton (Upper Cretaceous) age. Its name is 

 derived from Frontier, AVyo., where the 

 coals are well developed. The forma- 

 tion contains near the top a prominent 

 sandstone about 200 feet thick, which 

 usually forms a ridge at the outcrop and 

 is characterized by the presence of fossil 

 shells of a long, slender oyster (Ostrea 

 soleniscus). Since 1858, when 



Engle- 



fossils 



stone on Sulphur Creek, it has been a 

 favorite collecting ground for geologists, 



and from the time of the Ilaj-deu Survey, 

 in 1872, it has been known as the Oyster 

 Ridge sandstone. Fossil plants also have 

 been collected from theFrontier formation, 

 ^ The Beckwith formation comprises two 

 members. The lower member consists of 

 conglomerate, sandstone, and sandy clay 

 2,500 feet thick, light colored near the 

 railroad, but red farther north; the upper 

 member consists of light-colored sandstone 

 and clay about 3,000 feet thick well ex- 

 posed west of the railroad from Bridger to 

 Leroy and in the ridg^ west of the Aspen 



tunnel . 



