Vanadiferous Minerals in Western Colorado. 127 



their color to some chromium mineral. These occurrences are 

 interesting as showing that a green color in sandstones may 

 result from various causes, and that even a bright green tint 

 cannot be taken as an infallible indication of copper. 



The La Sal Creek deposits. — These occur in the extreme 

 western portion of Montrose County, southwest of Paradox, 

 and about six miles up La Sal Creek from Cashin P. O. They 

 are reached by trails from Paradox Valley and from Cashin. 

 The deposits are on the south side of La Sal Creek and about 

 700 feet above the stream. They occur for a distance esti- 

 mated at more than a quarter of a mile, along the sandstone 

 cliffs which descend from the mesa into the caiion of La Sal 

 Creek, and only a few feet below the level of the mesa surface. 



In the absence of continuous stratigraphic work, it is impos- 

 sible to correlate certainly and finally the rocks on La Sal 

 Creek with the divisions established by Cross and Spencer in 

 the Telluride quadrangle to the eastward. It seems probable, 

 however, that the La Plata sandstone attains a much greater 

 thickness in this portion of western Colorado than it does 

 between Telluride and Placerville. The limestone bed, so 

 characteristic a feature of the formation near Placerville and 

 further east, is not uniformly present in this western region, 

 and the La Plata sandstone (Variegated Beds, in part, of the 

 Hayden Survey) is not always readily differentiated from the 

 underlying Dolores formation (Red Beds). For a vertical dis- 

 tance of about 400 feet above the bed of La Sal Creek the rock 

 is a heavy-bedded, rather fine-grained, light-colored sandstone, 

 which is considered by Dr. Spencer to be the La Plata. Above 

 this come thinner-bedded sandstones, with some conglomerates 

 and shales, which are included in the McElmo formation. It 

 is in this upper series that the uraniferous deposits occur. All 

 the beds are here approximately horizontal. 



As revealed by numerous small openings near the crest of 

 the bluff, the carnotite, which is the material here sought, is 

 found chiefly in a massive bed of nearly white sandstone. 

 Some of the ore, however, lies between the sandstone and a 

 lower bed of light-gray shale. Although the prospecting open- 

 ings all lie at about the same level along the cliffs, the deposit 

 is not nearly so regular as the vanadiferous band near Placer- 

 ville. 



The carnotite of La Sal Creek occurs as irregular, bunchy 

 " pockets " in the sandstone, or along the contact of the sand- 

 stone with the underlying shale. These have all the appear- 

 ance of being impregnation deposits, the solutions carrying the 

 uranium compounds having deposited the ore wherever they 

 found ready passage through the rock — usually along bedding 

 planes. No roscoelite was detected with the carnotite. 



