GEOLOGIC MAP COMPILATIONS OF THE WALLACE AND KALISPELL 1° X 2° QUADRANGLES, IDAHO AND MONTANA, USA, AND ALBERTA AND BRITISH COLUMBIA, CANADA

The Wallace and Kalispell 1° x 2° quadrangles form the northwestern part of the Northern Rocky Mountains transect – a U.S. Geological Survey (USGS) project that aims to produce updated and integrated geologic maps of twelve 1° x 2° quadrangles in Idaho and Montana. Metasedimentary rocks of the Mesoproterozoic Belt Supergroup are widespread throughout the northern part of the transect and are the primary rock type found in the Wallace and Kalispell quadrangles. The original geologic map of the Wallace quadrangle was published by Jack Harrison and others (1986) as USGS Miscellaneous Investigations Series Map I-1509-A, and the original Kalispell map was published by Jack Harrison and others (1992) as USGS Miscellaneous Investigations Series Map I-2267-A. We are currently updating the geologic maps of both quadrangles by compiling more recent geologic maps, conducting stratigraphic studies, obtaining new and recently published age determinations for igneous rocks, and incorporating new geologic mapping from recent field work and interpretations of Lidar and satellite imagery.

Geologic maps of the Plains, Wallace, and Idaho part of the Thompson Falls 30’ x 60’ quadrangles published between 1999 and 2007 by USGS, Montana Bureau of Mines and Geology, and Idaho Geological Survey are the primary mapping sources that will update the southern half of the Wallace quadrangle. Additionally, 1:48,000 scale maps donated to USGS by Asarco and Cominco will be used to update western parts of both 1° x 2° quadrangles. Recent maps and our field observations indicate significantly fewer faults and more coherent stratigraphic successions than the original Wallace and Kalispell maps.

Fieldwork conducted from 2021 to 2023 provides new mapping of the Bison Range (Wallace quadrangle), stratigraphic data used to resolve the unnamed formation (eastern Kalispell quadrangle), and updated age determinations for igneous rocks throughout the map area. High resolution Lidar from the USGS 3D Elevation Program is being used to produce detailed maps of surficial units, including those related to Pleistocene glaciation in the Flathead River valley. These data sets are being prepared for publication as USGS data releases and will be incorporated into updated maps of the Wallace and Kalispell quadrangles.