Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Christopher J. Schmidt
Dr. James S. Monroe
Dr. W. Thomas Straw
Masters Thesis-Open Access
The Snowcrest Range was uplifted in Late Cretaceous and Early Tertiary time as a consequence of thrusting in Precambrian basement and Phanerozoic cover rocks.
The Snowcrest-Greenhorn thrust system is associated with largescale overturned, eastward verging folds. Mean orientation of the thrust system is N.40°E., 35°N.W.. The trend of the thrust system and associated transverse faults appear to be controlled by earlier structures. Mesoscopic and microscopic analyses indicate that metamorphic basement rocks accommodated congressional strain largely by brittle faulting and cataclastic shearing. Kinematic indicators suggest that local stresses were directed east-southeastward.
Northeast-trending Neogene faults along the western flank of the range follow the trend of the thrust system. Alistric-normal geometry for these faults is demonstrated by rotation of Tertiary beds along the range front. The position and inferred geometry of Neogene normal faults may, therefore, reflect localization of basin-range extension along zones of Laramide weakness.
Sheedlo, "Structural Geology of the Northern Snowcrest Range, Beaverhead and Madison Counties, Montana" (1984). Master's Theses. 1571.