Abstract

The Sawtooth Range is south of Glacier National Park and forms 85 miles of the Rocky Mountain front in northwestern Montana. The range averages 9 miles in width, consists of a broad northeastward-pointing arc, and extends north across the Saypo quadrangle.

The sedimentary rocks exposed in the Sawtooth Range are approximately 5500 feet thick, are Paleozoic and Mesozoic in age, and are divided into nine formations: Pagoda and Steamboat (Middle Cambrian), Switchback (Middle and Upper Cambrian), and Devils Glen (Upper Cambrian), unnamed formation (Upper Devonian), Hannan (Mississippian), Ellis (Upper Jurassic), and Kootenai and Colorado (Lower and Upper Cretaceous).

Three structural provinces occur in the central part of the Range: an eastern province, characterized by westward-dipping high-angle to moderately low-angle thrusts that increase in number northward; a central province, characterized by closely spaced, westward-dipping, high-angle thrusts, and by drag-folding of the Devonian and Mississippian rocks comprising the imbricated slices; and a western province, characterized by folded, low-angle overthrusts, above which the rocks are compressed into large open folds.

The structures were produced by stresses from the west during the Laramide orogeny. The mountains were maturely eroded during the Tertiary, when the east-west courses of the main streams were established. Uplift in the Pliocene? raised the range to its present altitude but did not cause additional deformation.

First Page Preview

First page PDF preview
You do not currently have access to this article.