Badlands at the foot of Scotts Bluff’s north face. Courtesy, Union Pacific Railroad.
Natural History of Scotts Bluff
Although Scotts Bluff is primarily significant because of its historical associations, its geology and biology are also interesting. Indeed, appreciation of the history of the bluff is enhanced by an understanding of how this bluff was formed and how it influenced migration routes. An elementary knowledge of the plant and animal life of the area, which is today much as it was in the covered wagon era, adds to your understanding of this story.
Elevations.
The highest point in the monument area is South Bluff, 4,692 feet above sea level. (The highest point in Nebraska, more than 5,000 feet, is in Banner County, south of Scotts Bluff.) The “high point” on Scotts Bluff proper is 4,649 feet, which is 766 feet above the North Platte River or 700 feet above the badlands at its immediate base. The elevation of monument headquarters is 4,114 feet.
Geology.
This bluff, like the neighboring Wildcat Hills, Chimney Rock, and Courthouse Rock, is an erosional remnant of the ancient Great Plains. These plains were formed by the deposit of gravel, sand, and silt brought down by rivers from the Rocky Mountains after they were uplifted about 60 million years ago. At intervals, 30 to 40 million years ago, volcanoes to the west also added great quantities of ash and dust deposits. When the process of deposit slowed, erosion gained headway, cutting new river valleys in the Plains. High tablelands were left on both sides of the North Platte Valley. Landmarks such as Scotts Bluff and Chimney Rock have hard rock caps that protect them from erosion.
The lower two-thirds of the bluff consists of Brule clay, an Oligocene deposit of buff-colored, soft-textured sandy clay. The badlands formation at the foot of the bluff dramatically demonstrates the rapid erosion of the Brule clay when unprotected by cap rock. The upper one-third of the bluff consists of the Arickaree formation, gray sand beds of the Miocene Epoch. The uppermost Arickaree beds form the top surface of the bluff. These are laced with hard tubular concretions which help protect the bluff and add to the resistance of the beds to weathering. All the formations exposed in the walls of the bluff are interspersed with thin layers of pinkish volcanic ash.