Devils Tower began as an intrusion of igneous material into sedimentary rock. An "intrusion" refers to the forcible movement of molten rock into (or between) other rock formations. As the molten rock cooled, the rock contracted, forming hexagon-shaped columns. When first formed, Devils Tower was covered by overlying layers of sedimentary rock including shale and sandstone. Through the process of erosion, Devils Tower, composed of harder rock, has become exposed. Over time, more of the tower will be exposed as erosion continues. However, erosion works two ways, and though more of the tower may be exposed, erosion also causes the tower to crumble over time. The rock pile at the base of the tower formed from this natural process in action.
The nearest cities to Devils Tower are Gillette, Wyoming; and Rapid City, South Dakota. These cities also house the nearest commercial airports to the tower. If you travel east on Interstate 90, exit at Moorcroft. If traveling west, take I-90 to Sundance. From Moorcroft or Sundance, take U.S. 14 north to state highway 24 north; this route will take you directly to Devils Tower.
Rock climbers recognize Devils Tower as a top-notch traditional crack-climbing site. Climbers should plan to bring along their own cams and stoppers, as climbing routes are not bolt-protected. If you plan to climb the tower, you are required to register (for free) prior to climbing and check in following the climb. During the summer months, register at the climber registration office next to the visitor center. Those planning to climb in the off-season should use the self-registration kiosk located at the center of the parking lot near the tower's base. During the month of June, climbers voluntarily stay off the tower in deference to its sacred significance to local Native American tribes. In addition, some climbing routes close between the months of March and July due to the nesting activities of prairie falcons.
If scaling the tower is not in your plans, you may opt to explore the area via one of the national monument's trails. Devils Tower features nearly eight miles of trails; the most popular trail is a 1.3-mile paved loop around the base of the tower. Other activities at the monument include ranger-led activities such as tower walks, ranger talks, evening programs, and full-moon walks. For visitors to Devils Tower during the winter months, activities include snowshoeing and cross-country skiing.
Belle Fourche Campground is a first-come, first-served campground located at the monument. The campground, open between mid-April and late October, has 50 individual sites and three group sites. It does not have RV hookups, showers or a dump station. The fee for campground use is $12 per day.
You can visit Devils Tower National Monument 365 days a year. The visitor center, which features interpretive exhibits, is open between early April and late November. Visitor center hours vary throughout the year, but typically include the core hours of 9 a.m. to 5 p.m. Hours run longer during the peak summer season. The entrance fee for Devils Tower is $10 per vehicle, and $5 per motorcycle or individual (hiker or bicyclist). Admission is valid for a period of seven days.