Geology of Big Sheep Creek Canyon, Southwest Montana

Описание: This video centers on some aspects of the geology of the Big Sheep Creek Canyon of southwest Montana. The canyon of Big Sheep Creek is located a few miles south of Dell, Montana, and is accessed via the Big Sheep Creek Backcountry Byway. The canyon is a great place to see the Mississippian Madison Limestone, karst features within it, and folding and faulting it endured during the Cretaceous "Severe orogeny." This is also a superb place to see a recent fault scarp. The Red Rock fault scarp cuts Pleistocene outwash, so must be no older than about 12,000 years, but trenching shows it is likely only a few thousands years old and a composite of several ground ruptures.

The fault is the result of the passage of the Yellowstone hot spot thermal bulge to the northeast, which caused raised crust around the bulge in southwest Montana to collapse starting around 4.5 million years ago. This disrupted the path of the ancestral Missouri River, diverting it into newly-formed NW-trending grabens, like the Red Rock Valley, and resulting in NE-trending canyon cuts where mountains were raised into the path of the ancestral river, like the Big Sheep Creek canyon. Big Sheep Creek has an interesting and complex fisheries that directly reflects the geologic influences on the geomorphology of the stream.