The following report presents measured sections and lithostratigraphic correlations of the units in the order to document a syntectonic unconformity in order to understand the tectonic history of the area.

This report gives a brief geological description of the Clark Fork quadrangle on the Idaho-Montana border.

This report follows geological studies of the Duck Creek Pass quadrangle, Montana during the summers of 1956 and 1957.

From abstract: The origin of the gneissic rocks on the eastern border of the Idaho batholith in the Bitterroot Range, near Hamilton, Mont., has long been in dispute. Lindgren regarded these rocks as the product of stresses related to a normal fault along the front of the range with an eastward dip of about 150. He thought both the hanging wall and the footwall had moved, with a total displacement along the fault plane of at least 20,000 feet. The faulting was believed to have been so recent as to be a major factor in the present topography. Langton appears to accept the concept of faulting but to regard the gneissic rocks as formed much earlier from a granitic rock that was more silicic and older than the Idaho batholith.