GEOLOGIC MAP OF THE SOUTHERN WHITEFISH RANGE, MONTANA

The Whitefish Range in northwestern Montana lies west of Glacier National Park between two fault-bounded basins, the Rocky Mountain Trench to the west and the Kishenehn Basin to the east. This newly compiled ArcGIS map using ArcMap 10.8 resurrects three USGS 7.5 minute quadrangles (Huckleberry Mountain, Skookoleel Creek, Werner Peak) transecting the southern Whitefish Range originally mapped as part of MS theses at the University of Wisconsin-Madison in the late 1980s (T.S. Hanson, S.P. Lundblad, J.F. Reese). This geologic map and cross section complements a recent data release updating GIS files for the Kalispell 1 x 2 degree sheet with detailed mapping at 1:24,000 scale.

Belt Supergroup rocks comprise the southern part of the range. Units present in the map area range from the upper Prichard Formation through the McNamara Formation. The area is part of a large, open, north-northwest-trending monocline likely related to the development of the Whitefish Duplex structure associated with the Lewis Thrust Fault. Several major northwest trending faults cut the area. They are mainly inferred from thickness anomalies of stratigraphic units, attitude changes, increased cleavage intensity, and offset layers. Northwest-trending normal faults separate the Rocky Mountain Trench from the western edge of the range and bound the North Fork Flathead River valley on the eastern edge of the mapped area. The southern extension of the Whitefish Thrust Fault is identified just east of the Whitefish Divide by anomalies in stratigraphic thickness and change in bedding attitude. It diffuses into a series of open SE plunging folds in the southern part of the map area.