274 Subsurface Geologic Methods 



edge of the Powder River Basin, where the influence of primary alkaline 

 waters from the Big Horn Mountains is indicated at Billy Creek, and the 

 influence of secondary saline surface waters can be traced in the Salt 

 Creek area. 



In general, the presence of a secondary saline water in Cretaceous 

 and younger sands of Wyoming indicate surface-water infiltration or 

 contamination. Sulphate is absent or negligible in Cretaceous waters, and 

 the presence of this radicle almost invariably indicates drilling-water con- 

 tamination, particularly as sulphate is the dominant negative ion in most 

 surface waters. The presence of sulphate in persistent and notable quanti- 

 ties usually is not encountered below the ground-water zone until Juras- 

 sic beds are reached. Below the Jurassic, however, sulphate is usually the 

 principal negative ion. 



Tertiary 



Tertiary beds of unconsolidated variegated shales and sandstones 

 cover most of the plain and basin areas of the Rocky Mountain region with 

 thicknesses up to more than 30,000 feet. Most of these sands are not pro- 

 ductive of commercial oil or gas. Small amounts of oil and gas have been 

 produced from the White River formations of Oligocene age at Shawnee, 

 Douglas, and Brenning Basin in central-eastern Wyoming, and oil and 

 gas are being produced commercially from lenticular sand bodies in the 

 Wasatch formation of Eocene age at Hiawatha and Powder Wash, Colo- 

 rado, and La Barge, Wyoming. 



With the exception of the above-mentioned producing fields, the 

 water analyses available from Tertiary sands were sampled for drilling 

 use and do not reflect the stagnant conditions associated with oil-field 

 waters. 



Green River Formation 



An exceptional type of water has been encountered in a few wells 

 drilled into the lacustrine Green River formation of Eocene age. The for- 

 mation consists of sandstone, marl, limestone, and sandy shale, with thin 

 beds of oil shale, halite, glauberite, and trona. These salts have influenced 

 the composition of the ground water in this area with the result that so- 

 dium carbonate occupies 60 percent of the dissolved salt content of the 

 water, sodium chloride 37 percent, and sodium sulphate 3 percent. Total 

 solids range from 40,000 to 80,000 parts per million, and the water has 

 been used for the production of crude soda ash. 



Wasatch Formation 



The Wasatch formation at Hiawatha and Powder Wash, Colorado, 

 consists of more than 5,000 feet of shale containing irregular and lenticu- 

 lar fluviatile and lacustrine porous sands. Oil and gas production at Hia- 

 watha comes from three lenticular oil sands between depths of 2,032 and 



