The conterminous United States mineral-resource assessment program : background information to accompany folios of geologic and mineral-resource maps of the Harrison 1⁰x2⁰ quadrangle, Missouri and Arkansas, and the Joplin 1⁰x2⁰ quadrangle, Kansas and Missouri - Pratt, Walden P., 1928- (U.S. Geological Survey circular ;, 1997)