Geology of the north end of the Ruby Range, southwestern Montana

Abstract

This study consists of two parts: stratigraphy and sedimentation, and structure of rocks in the northern one-third of the Ruby Range of southwestern Montana. Detailed studies of Cambrian marine dolomite rocks in the Red Lion Formation and in the upper part of the Pilgrim Limestone resulted in their division into distinct rock units, termed lithofacies. These lithofacies contain features suggestive of subtidal, intertidal, and supratidal environments similar to those presently forming in the Persian Gulf. Stromatolitic structures occurring in the uppermost part of the Red Lion Formation are similar to those presently forming in Shark Bay, Australia.

Mineral resources of the Ruby Mountains Wilderness Study Area, Madison County, Montana

“…The final stage of the orogeny is recorded in the placement of discrete blocks of Archean and Paleozoic strata along the west, north, and to a lesser extent, the east flank of the northern third of the Ruby Range. These blocks were interpreted as gravity slide blocks by Tysdal (1970Tysdal ( , 1976a, although Schmidt and Garihan (1983, map p. 274) interpreted a few of those along the western side of the mountains as thrust slices. The northern part of the range is flanked by Tertiary normal faults, which separate the mountains from the basins.…”

Cenozoic block uplifts in east-central Idaho and southwest Montana

“…The Ruby Range block uplift was mapped and described by Tysdal (1970Tysdal ( , 1976a, who concluded that uplift of the range and folding of the sedimentary rocks was a result of differential vertical movements of discrete basement blocks (Tysdal, 1970, p. 105-119). Swanson (1970, p. 670, 718-719) interpreted most of the steep faults of southwest Montana as reverse faults reflecting vertical movements along ancient shear zones, and he attributed much of the folding in this region to draping over uplifted, fault-bounded, rigid basement blocks of Archean crystalline rocks.…”