Article Four of the United States Constitution
The federal government owns or controls about thirty percent of the land in the United States. These holdings include national parks, national forests, recreation areas, wildlife refuges, vast tracts of range and public lands managed by the Bureau of Land Management, reservations held in trust for Native American tribes, military bases, and ordinary federal buildings and installations. Although federal property can be found in every state, the largest concentrations are in the west, where, for example, the federal government owns over eighty percent of the land within Nevada.