Geology Shaping History

The Pine Bluffs were formed by early geologic activity followed by millions of years of weathering, leaving an erosion-resistant caprock of sandstone and claystone atop softer clay that erodes away until sections collapse down the cliff face. Draws and ridge lines support clusters of mountain mahogany, ponderosa pines, limber pine, grasses, and forbs, creating woodland islands that provided habitat for many plants and animals and attracted Native Americans from throughout the region to forage and hunt. The uplift of the Laramie Mountains left a narrow remnant of sedimentary rock extending into the mountains between Cheyenne and Laramie, a feature known as the Gangplank that offers a gradual westward ascent through the mountains. In 1865, while scouting routes through the Rocky Mountains, General Grenville M. Dodge found a ramp-like ridge leading to the plains without a break, and in 1866, as chief engineer for the Union Pacific, he determined that the Gangplank was the best route for building the Transcontinental Railroad because its gentle rise was not too steep for locomotives. This natural travel corridor to the granite summit remains in use, and along it twenty miles west of Cheyenne the Dale Creek Trestle, completed in 1868, became an engineering marvel, a 450 foot long wooden bridge that swayed in the wind as trains crossed.

Pine Bluffs, Wyoming · United States