Metamorphic Petrology and Structure of the St. Joe Area, Idaho
Purpose and Scope The study of the St. Joe area was done cooperatively by the Northern Pacific Railway Company and the Idaho Bureau of Mines and Geology to map the geology and to evaluate the mineral potential. The mineral evaluation was described in a private company report (1963). The geologic part of the study by the Bureau of Mines and Geology covered 2,440 km 2 . The St. Joe area is an excellent example of progressive regional metamorphism with good stratigraphic control; changes in structural development are well illustrated. This study is carried into the kyanite zone; the sillimanite zone was studied by Juras (1974). Location The St. Joe area lies in northern daho, north of the Clearwater River (Fig. 1). Most of the area drains into the St. Joe River, except for a small part on the south which drains to the Little North Fork of the Clearwater River. Altitudes range from a low of 648 m (2,140 ft) on the St. Joe River to a high of 2,330 m (7,690 ft) at Illinois Peak. Average relief is in the range of 758 to 909 m (2,500 to 3,000 ft). The valleys are mostly deep and V-shaped; minor glaciation has occurred at a few of the higher peaks.