Shoshone Canyon

The panel explains how the river cut this gorge but not why it went through the mountain instead of around it. Geologists call the Shoshone a superposed river: it set its course on younger deposits that once buried the fold, then held that course as the basin was stripped away and sawed down into the hard rock beneath, splitting one anticline into Rattlesnake Mountain on the north and Cedar Mountain on the south. The panel's two billion years for the granite at the dam is low; the state geological survey puts it at 2.5 to 2.8 billion.

What the plaque says

Shoshone Canyon Shoshone Canyon is a gorge cut through Rattlesnake Mountain by the wearing action of the Shoshone River. The mountain is a northwest trending uplift in the earth's crust that rises 3700 feet above the surrounding terrain. Beds of sedimentary rock that are exposed on the mountain's northeast flank slope eastward beneath the plains. The same units, which range in age from 205 to 570 million years, bend up and over the crest of the mountain and stand vertically along the southwest flank. Granite exposed at the west end of the canyon at Buffalo Bill Dam is two billion years old. North of the dam, a fault (crack) in the earth's surface lies adjacent to the steeply inclined rocks. Geologic compressive forces which formed the uplift also caused rocks to move 2000 feet vertically along the fault. The Rattlesnake Mountain uplift began to form 66 million years ago, approximately the same time dinosaurs became extinct. The present topographic configuration of Rattlesnake Mountain and the formation of Shoshone Canyon are due to erosional downcutting occurring over the past three million years.

Where it stands

Worth the stop nearby

• Old Trail Town — 1.8 mi
  Bob Edgar's rescued log buildings, outlaw cabins and an Apsáalooke scout's home among them, rebuilt on the ground where Cody City was first laid out.
• Buffalo Bill Center of the West — 3.4 mi
  A memorial begun the year Buffalo Bill died that grew, wing by stone-walled wing, into five museums and a library under one roof.
• Heart Mountain Interpretive Center — 15 mi
  The incarcerated cleared and watered the land; when the camp closed it went to veterans to homestead, and the barracks sold for a dollar each.

More markers nearby

• Colter's Hell — 1.1 mi
• Wyoming Vietnam Veterans Memorial — 4.9 mi
• Castle Rock — 12 mi
• Dead Indian Hill Summit — 20 mi