Scotts Bluff is located in western Nebraska and towers more than 800 feet above the North Platte River. The bluff served as an important landmark on the Oregon Trail, California Trail and Pony Express Trail, and was visible at a distance from the Mormon Trail. Over 250,000 westward emigrants passed by Scotts Bluff between 1843 and 1869 and it was the second most referred to landmark in pioneer journals and diaries (after Chimney Rock).
Scotts Bluff is an outlier formation of the Wildcat Hills, visible to the south. 22 million years ago, the surface of the plains were as high as Scotts Bluff and they were a gently sloping landscape composed of sediments from the mountains to the west. Roughly 3 million years ago, the Platte River and its tributaries began to erode the high plains and little by little, water carried away soil and rocks, creating canyons that grew wider and wider. All that remains today of these ancient high plains are Wildcat Hills, Scotts Bluff, and other erosion resistant remnants.
The listed coordinates will bring you to South Overlook, which offers an amazing view in all directions. The two biggest processes that can be observed here is weathering and erosion. Both processes often work together, weathering breaks down the rock while erosion moves the broken pieces of rock (you may sometimes hear it referred to as mass wasting). For this earthcache, we will focusing on weathering. Weathering is the process by which rocks, soil, and minerals are broken down through contact with Earth's atmosphere, water, and biologic resources. There are three types of weathering, physical, chemical, and biological. Physical weathering is primarily caused through frost wedging, when water seeps into cracks within the rock, and when the water freezes, it expands. This process continues until eventually a piece of the rock breaks away. If you look behind you, you'll see Saddle Rock and at the base of it you may notice remnants of rockfalls. Another example of physical weathering is exfoliation. This occurs when cracks develop parallel to land surfaces, and it almost looks like "layers" of the rock are being broken apart. Chemical weathering takes place when rain water reacts with minerals within the rock. In most cases, the water is slightly acidic. Lastly, biological weathering takes place when tree roots grow in between cracks within rocks, and as the root grows, it breaks apart the rock. Algae and lichen that live on rock may also produce chemicals that break down the rock so they can obtain the nutrients needed to survive.
Logging Requirements:
- Looking at Saddle Rock (behind you), you'll notice at the far right side that there is a crack, how do you think it was formed and what do you think will eventually happen?
- Describe Saddle Rock, is the color of the layers consistent or does it vary? Also, does weathering appear consistent or does it look like some parts of the formation are weathered/eroded more easily than others? Why do you think this is the case?
- From the overlook, looking straight ahead you'll see one of the tunnels that you drove through on your way here. Describe the surrounding cliff face. Do you see any signs of weathering? If so, what form is visible? Why do you think the tunnel was lined with concrete?
- Upload a photo taken from the South Overlook. You do not need to be in the photo, though it is strongly encouraged.