Evidence of erosion is visible everywhere you turn in Big Bend National Park. A great example of the power of water and gravity on rock is located just up the road. Keep an eye on your left, where a large scar on the Santiago Mountains marks the spot. Late one evening in 1987, a rockslide occurred along this cliff face, creating a tremendous noise that was heard by park staff at Persimmon Gap. Soft Del Rio claystones located directly underneath hard Santa Elena limestone eroded, undercutting the limestone cliff until portions of it collapsed. Even though it appears to have happened yesterday, this scar is a testament to the vast amount of time that it takes for erosion to wear down the mountains of West Texas.