National Parks
National Monuments
National Historical Parks, Memorials, and Battlefields
National Recreation Areas, Seashores and Trails
Other Preserves and Protected Areas
... 31.2% from 45 to 64, and 9.4% who are 65 years of age or older. The median age is 42 years. For every 100 females there are 126.2 males. For every 100 females age 18 ...