Devil’s Tower National Monument, northeastern Wyoming, established 1906, the first national monument in the United States. Devils Tower is a natural rock formation that resembles a giant petrified tree stump. Rising 390 m (1,280 ft) above the valley of the Belle Fourche River, it has an area at its top of 0.6 hectares (1.5 acres). The formation, of volcanic origin, is more erosion-resistant than the surrounding rock, which has been worn away. Area, 545 hectares (1,347 acres).
