From abstract: The U. S. Geological Survey made a geophysical investigation on the Gramlich group, Paradox district, Montrose County, Colo., during the period May 26 to July 11, 1952.. Electrical resistivity and self-potential surveys were made to determine the thickness of the upper Salt Wash sandstone and to test electrical prospecting methods in an area of shallow overburden. The investigations were made in conjunction with a diamond-drilling program.