The United States has 63 national parks, which are congressionally designated protected areas operated by the National Park Service, an agency of the Department of the Interior. National parks are designated for their natural beauty, unique geological features, diverse ecosystems, and recreational opportunities, typically "because of some outstanding scenic feature or natural phenomena." While legislatively all units of the National Park System are considered equal with the same mission, national parks are generally larger and more of a destination, and hunting and extractive activities are prohibited. National monuments, on the other hand, are also frequently protected for their historical or archaeological significance. Eight national parks are paired with a national preserve, areas with different levels of protection that are administered together but considered separate units and whose areas are not included in the figures below. The 433 units of the National Park System can be broadly referred to as national parks, but most have other formal designations.