Ground-water investigations were made by the Ground Water Branch, U. S. Geological Survey, from 1946 to 1954, inclusive, in several parts of Montana. These studies were made as part of the program of the Department of the Interior for development of the Missouri River Basin. Thus, the areas selected for study were principally those in which construction agencies such as the U.S. Bureau or Reclamation and the U. S. Bureau of Indian Affairs had problems relating to ground water. Figure 1 shows the areas in Montana in which ground-water studies have been made under the Missouri Basin Program from 1946 to 1954, inclusive.