Geologic map of the Sedan quadangle, Gallatin and Park Counties, Montana

This quadrangle lies 6.4 km (4 mi) northeast of Bozeman, Mont., in southwestern Montana. Metamorphic, sedimentary, and volcanic rocks of Precambrian to Tertiary age are exposed in the Bridger Range and southwestern margin of the Crazy Mountains Basin in a crustal cross section and a structural triangle zone. Surface geology records Precambrian extension, Late Paleocene east-vergent contraction, including backthrusts, and Holocene basin-range extension.