Rushmore Cave Rushmore Cave Rushmore Cave is the closest show cave to Mount Rushmore National Memorial in the United States. It contains a wide variety of natural formations. It is the ninth longest cave in South Dakota. It measures a distance of . It was discovered in 1876 when a log flume that supplied water to mining operations in town of Hayward broke and spilled onto the side of the hill. As the water flowed down the hill it started flowing into a small hole in the hillside. The local miners who went up to fix the flume noticed this abnormality and
Mount Rushmore selected Mount Rushmore as the site for several reasons. The rock of the mountain is composed of smooth, fine-grained granite. The durable granite erodes only every 10,000 years, thus was more than sturdy enough to support the sculpture and its long-term exposure. The mountain's height of above sea level made it suitable, and because it faces the southeast, the workers also had the advantage of sunlight for most of the day. The Mount Rushmore area is underlain by well drained alfisol soils of very gravelly loam (Mocmount) to silt loam (Buska) texture, brown to dark grayish brown. Mount Rushmore has