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

The geology of the Sedan quadrangle was mapped as part of a regional study of
the western Crazy Mountains Basin. It was digitized for ease of production of
the printed version and for greater distribution for analytical use.

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.

A preliminary map was published as a U.S. Geological Survey Open-File Report in
1971. The geologic data was interpreted 1965-93, the interpretation being
informed by data from two wells in addition to the original field work. The
digital files for the map were released in November 1998. The map-on-demand
edition, released in January 2000, includes supplemental figures,three cross
sections, and interpretive text.

Users should be aware that of the many faults mapped, the only active one is
the range front fault on the west side of the Bridger Range.

The dataset for the Sedan quadrangle consists of 10 coverages:
geo_net, geo_pnt, stru_net, stru_pnt, data_net, data_pnt, pnt_sym,
pnt_graphic, stpnt_graphic, and dvalues. The three coverages
pnt_graphic, stpnt_graphic, and dvalues are not "true" ARC/INFO
coverages. They contain the graphic representations of symbols used
on the geologic map:

>pnt_sym = pnt_graphic,
>stru_pnt and geo_pnt = stpnt_graphic, and
>dvalues = annotation for stru_pnt and geo_pnt.