It is located on the border of the states of Colorado, Arizona, Wyoming, and Utah, near the mouth of the Yampa River into the Green River. The monument was established by a decision of President Woodrow Wilson in 1915, on an area of 0.32 square kilometers. Today, it covers an area of 853.26 square kilometers.
The monument contains thousands of bones belonging to 10 species of dinosaurs. The first fossil skeleton of an Apatosaurus was discovered in the area in 1909 by paleontologist Earl Douglass.
The park also contains numerous petroglyphs and cave pictographs of Indians who lived in the area.
