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The Townsend Valley in west-central Montana is a 600 square-mile intermontane basin bordered by the Big Belt Mountains on the east and by the Elkhorn Mountains on the west. It extends from approximately T. 4 N., to T. 11 N., inclusive. Rocks ranging in age from Precambrian to Cretaceous crop out in the mountainous areas that surround the valley, and rocks of Tertiary (Oligocene and Miocene) age crop out on the higher valley slopes and underlie the alluvial deposits in the valley bottom. The area is drained by the Missouri River, which enters the Townsend Valley through a gorge at the southern end of the valley and leaves through another gorge at the northern end. The climate of the valley is semi arid; the average annual precipitation is 12.35 inches. Farming is the principal occupation. About one-third of the cultivated land is irrigated by water diverted from the Missouri River and perennial mountain streams, and the remaining cultivated land is farmed by dryland methods. Wheat, oats, barley, sugar beets, and potatoes! are the principal crops. Mining, which was once the chief industry of the area, is now (1951) sporadic and on a small scale. Gold, silver, and lead are the chief metals mined. Small amounts of coal, marble, quartzite, and iron ore have been mined during the past 10 years. A large reservoir of ground water underlies the valley. On the valley floor shallow well s yield an abundant supply of water for domestic and stock use, but on the higher slopes wells must be drilled to a depth of 200 to 300 feet to obtain an adequate supply. Water is confined under artesian pressure in Tertiary beds that underlie the southern end of the valley and the area along the west flank of the Dry Creek anticline east of Townsend. The denser pre-Tertiary formations contain water in fissures and small openings and springs are numerous where these rocks crop out. Big and Plunket (Mockel) Springs, which yield about 57 and 8.7 cfs, respectively, are the largest. The principal sources of recharge to ground water in the younger, unconsolidated deposits are streams, irrigation canals and laterals, and irrigation floodwater. About 8,500 acres of the land is waterlogged because the transmissibility of the underlying waterbearing materials is low or because the configuration of the bedrock is such that the movement of ground water is restricted. Of this total, 1,500 acres will be inundated by water impounded by the Canyon Ferry dam. Drainage of the remaining waterlogged land would greatly increase the agricultural potential of the valley. Irrigation utilizing ground-water resources is in a pioneering stage in the Townsend Valley. In the summer of 1950 the first well for irrigation supply was drilled 3% miles southeast of Townsend and when tested, using air compressors, produced about 240 gpm.

Geology and occurrence of ground water in the Townsend Valley, Montana