The United States has 58 protected areas known as national parks, which are operated by the National Park Service, an agency of the Department of the Interior. National parks must be established by an act of the United States Congress. The first national park, Yellowstone, was signed into law by President Ulysses S. Grant in 1872, followed by Sequoia and Yosemite in 1890. The Organic Act of 1916 created the National Park Service "to conserve the scenery and the natural and historic objects and wildlife therein, and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations." National parks usually have a variety of natural resources over large areas. Many of them had been previously protected as National Monuments by the President under the Antiquities Act before being upgraded by Congress. Seven national parks are paired with a National Preserve, six of which are in Alaska. While administered together, they are considered as separate units and their areas are not included in the figures below. The newest national park is Great Sand Dunes, established in 2004.