National Parks
National Monuments
National Historical Parks, Memorials, and Battlefields
National Recreation Areas, Seashores and Trails
Other Preserves and Protected Areas
... 23.8% from 45 to 64, and 7.9% who are 65 years of age or older. The median age is 35 years. For every 100 females there are 95.1 males. For every 100 females age 18 ...