Subsurface Laboratory Methods 275 



2,512 feet, and at Powder Wash from zones logged in one well at 3,087 to 

 3,113 feet and 5,014 to 5,023 feet. The formation contains numerous 

 water-bearing lenticular sand bodies in addition to the oil- and gas-pro- 

 ducing zones. 



The La Barge field in western Wyoming produces oil from the Wa- 

 satch formation. The producing zone, at depths of 650 to 1,100 feet, 

 consists of two to three divisions, the upper a persistent sandstone aver- 

 aging about twenty feet in thickness, and the lower a series of sandstones 

 separated by interfingering shale beds that vary greatly in thickness. 



Wasatch waters are, on the whole, saline, the salinity being due al- 

 most entirely to the chloride ion. Concentrations range in total solids 

 from 1,500 to as much as 32,000 parts per million at Hiawatha and Powder 

 Wash, and from 3,000 to 12,000 parts per m-illion at La Barge. The more 

 concentrated and saline water at La Barge occurs in the lower and less- 

 continuous zones. Secondary characteristics are relatively low, though 

 variable, in the Colorado Wasatch waters and are negligible in the La 

 Barge waters. 



Lenticularity and lack of continuity are indicated by the erratic and 

 variable nature of the Hiawatha and Powder Wash waters. The uniformity 

 of the La Barge analyses points to the more continuous nature of the 

 sandstones. Representative Wasatch waters are tabulated in table 9. 



Upper Cretaceous 



Upper Cretaceous beds have yielded a major portion of the oil and 

 gas production in the Rocky Mountain region and, although overshadowed 

 now by pre-Triassic exploration, do and will continue to hold an im- 

 portant place in Rocky Mountain oil production. A basal sandstone of the 

 Mesaverde formation has produced some oil at Simpson Ridge, Wyoming, 

 and is producing oil now at West Poison Spider, Wyoming. The principal 

 Upper Cretaceous oil-producing zones in Wyoming are the Wall Creek 

 and equivalent sandstone beds of the Frontier formation and the Muddy 

 (Newcastle) sandstone member of the Thermopolis shale. 



Oil production from Upper Cretaceous sands in Montana has been 

 limited to a few areas, the most important being Cat Creek, but these 

 sands are important gas producers throughout the Great Plains region of 

 the state. 



There has been some oil and gas production from Upper Cretaceous 

 beds in Colorado, principally from fractured sandy zones in the Mancos 

 shale, but Lower Cretaceous and older beds are the more prolific horizons. 



Montana Group 



Montana-group waters are important in oil-field operations in the 

 state of Montana more for identification of intrusive water than for any 

 other purpose. With the exception of gas-producing fields, surface-water 



