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Surficial Geologic Map and Quaternary Tectonics of the Madison Valley and Fault Zone, Madison, Gallatin, and Beaverhead Counties, Southwest Montana

Scientific Investigations Map 3508
National Cooperative Geologic Mapping Program
By:  and 
https://doi.org/10.3133/sim3508

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Abstract

The north-northwest-striking Madison fault is approximately 95 kilometers in length, lying at the confluence of the northeastern Basin and Range province and the Yellowstone tectonic parabola. The fault zone consists primarily of west-dipping normal faults that have east-dipping antithetic faults, which create the Madison Valley graben and several northeast-trending intrabasin faults. The Madison fault and associated sections discussed herein refer to the main west-dipping, range-bounding fault along the eastern side of the valley. Detailed geologic mapping (1:12,000 scale) of the entire fault zone and fault scarp profiling (total of 102 profiles) of the Madison fault reveal greater late Quaternary paleoseismic activity towards the south, including at least three paleoevents along the southern part of the fault that postdate Pinedale glaciation. Early to middle Holocene alluvial fans have vertical surface offsets that average between 2.0 and 3.0 meters and define the characteristic single-event surface offset. Pinedale lateral moraines have vertical surface offsets as great as 12.0 meters. Late Pleistocene to Holocene multiple-event fault scarps show little evidence of beveling, suggesting short seismic recurrence intervals and potential late Pleistocene and Holocene temporal clustering. Long-term average tectonic activity rates indicate slip rates ranging from 0.18–0.6 millimeters per year. Based on a comparison of fault-scarp height versus maximum slope angle of known regression lines developed from other paleoseismic investigations, the most recent event ranges from 5–1 ka.

The northern section of the fault zone is defined by multiple normal faults, which detached the hanging walls of Laramide thrust faults within the Paleozoic and Mesozoic strata. This resulted in the partitioning of extension along multiple preexisting structures and less displacement along individual normal fault strands. Structural controls on lateral propagation of individual paleoevents involve the position of lateral ramps along preexisting Laramide contractional faults. This resulted in greater displacement within the larger basement-cored structures along the southern section of the fault zone, where extension is accommodated by one inferred principal basement-involved normal fault. Inferred east-northeast trending, intrabasin, normal faults within the southern half of the fault zone have no late Pleistocene displacement.

Suggested Citation

Ruleman, C.A., and Brandt, T.R., 2025, Surficial geology and Quaternary tectonics of the Madison Valley and fault zone, Madison, Gallatin, and Beaverhead Counties, southwest Montana: U.S. Geological Survey Scientific Investigations Map 3508, 1 sheet, scale 1:50,000, 45-p. pamphlet, https://doi.org/10.3133/sim3508.

ISSN: 2329-132X (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Geologic Setting
  • Quaternary Deposits and Depositional History
  • Morphometric Analyses
  • Seismic Hazard Assessment
  • Description of Map Units
  • References Cited
  • Appendix 1. Fault Scarp Profiles
  • Appendix 2. Vf Values
  • Appendix 3. Basal Facet Heights
Publication type Report
Publication Subtype USGS Numbered Series
Title Surficial geology and Quaternary tectonics of the Madison Valley and fault zone, Madison, Gallatin, and Beaverhead Counties, southwest Montana
Series title Scientific Investigations Map
Series number 3508
DOI 10.3133/sim3508
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Geosciences and Environmental Change Science Center
Description Report: viii, 43 p.; 2 Sheets: 31.40 x 70.84 inches ; Data Release
Country United States
State Idaho, Montana, Wyoming
County Beaverhead County, Gallatin County, Madison County
Other Geospatial Madison Valley and fault zone
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
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