The Shining Mountains

The Madison Range rises from the east side of the Madison Valley along the active Madison fault that threads its way along the base of the range. The mountains began to slowly rise along the fault about 50 million years ago and remains active today. This was violently demonstrated on August 17, 1959 when a magnitude 7.5 earthquake struck the southern end of the Madison Range near Hebgen Lake. The earthquake triggered a massive landslide that dammed the Madison River creating Earthquake Lake and killed 29 people. Fault scarps as much as 21-feet high significantly changed the landscape of the area. Young scarps are visible in the valley sediment along the length of the zone. Several prominent peaks in the northern Madison Range, such as Lone, Pioneer, and Fan mountains, are held up by resistant igneous rock that developed from magma that moved upward along cracks and laterally along the layers of sedimentary rock. Mountain glaciers and landslides carved the peaks into the shapes we see today. A well-known peak, Sphinx Mountain, and a smaller adjacent peak, The Helmet, are unique in the Madison Range because they are topped by 3,000 feet of conglomerates that serves as a cap rock, protecting the underlying softer rock from erosion. The gravels that became these conglomerates were eroded from surrounding highlands and were deposited in an ancient valley that now is part of the highest peaks. The Madison Valley also has its own spectacular features. Alluvial fans (so named because of their fan shapes as seen from above) formed as mountain streams deposited their sediment at the base of the mountains. The Cedar Creek Alluvial Fan is the biggest and most famous of the alluvial fans. Most of the deposits carried out of the mountains and into the fans ware glacial deposits. The mountains bordering the Madison Valley provided a spectacular backdrop to one of the most thrilling periods in the history of the American West, the fur trade. Beginning in the 1830s, trappers from American and Canadian fur companies frequently trapped beaver in streams emptying into the Madison River. Mountain men were frequent visitors to the valley and knew its topography well. The fur trade was a cutthroat business in the early 19th century as the fur companies and their employees competed for a limited and rapidly dwindling resource. That competition came to a head in October 1832 when Jim Bridger and business partner Thomas Fitzpatrick led a rival trapping brigade commanded by Henry Vanderburgh into a deadly ambush by the Blackfeet Indians. Within a few years, the Blackfeet had been decimated by smallpox and the beaver had all but disappeared from this area. The mountain men’s legacy lives on, however, in the names of many geographic features in the region.