A national park is generally a large tract of land that contains a variety of resources or an entire natural system, and is established by an act of Congress. A national monument is generally smaller than a national park and is intended to preserve a single nationally significant resource, such as a dunefield or rock formation. National monuments require only a presidential proclamation without a vote of Congress. A national preserve is an area managed by the National Park Service where certain activities that are prohibited within a national park may be permitted. For example, hunting is allowed in the Great Sand Dunes National Preserve, as it was when it was managed by the United States Forest Service. Great Sand Dunes was made a national monument in 1932 by president Herbert Hoover, protecting only the main dunefield.