The quadrangle includes portions of the Colorado Plateau and southern Rocky Mountains Physiographic Provinces. The entire area of the Gunnison Uplift and parts of the Uncompahgre and Sawatch Uplifts are included. A part of the Piceance Basin and a segment of the Rio Grande Rift Valley are also included. A basement complex of Precambrian metamorphic and igneous rocks is exposed in the core of the Gunnison and Sawatch Uplifts in the Southern Rocky Mountains. Jurassic and Cretaceous age sedimentary rocks lie directly on the Precambrian basement in most places. They lie on Paleozoic rocks at the west edge of the Sawatch Uplift in the north-central part of the quadrangle. Triassic beds are mapped only in the canyon of the Uncompahgre River near the southwest corner of the quadrangle. A suite of Tertiary volcanics and some sedimentary rocks occupy extensive areas. Plutonic rocks of Tertiary and laramide age occupy only a small part of the quadrangle. The literature consulted included information on about 100 separate occurrences of radioactive minerals and/or anomalous radioactivity within the quadrangle. Many fracture and stratigraphically controlled forms are reported. Most of these occurrences are clustered in three areas: Cochetopa Creek, Cebolla Creek, and Marshall Pass. Important uranium …