Geochemical relationships of water in the Powder River basin, Wyoming and Montana

Abstract

Geologic factors largely determine the composition and the amounts of dissolved solids that are transported by the Powder River and its tributaries. The chemical character of the water in the basin differs widely from one stream to another and is variable in each stream from headwaters to mouth. Mountainous areas underlain by igneous rocks of Precambrian age contribute small quantities of soluble materials to the river system; the concentration of mineral solids may be less than 50 ppm. Streams heading in upland country and draining a region that is largely underlain by Tertiary sandstones and shales transport salts in concentrations exceeding 2000 ppm. The composition of mineral substance in the river water can be correlated with occurrence in the area of such rocks as granite, limestone, gypsum, and shale.