• JUNE 1909: Nathaniel Galloway and son, Parley, are credited with first descent of the Yampa River Canyon by boat.
• AUG. 17, 1909: Earl Douglass, Carnegie Museum paleontologist, discovers eight vertebrae of an apatosaurus, the first skeleton discovered and excavated at the Dinosaur Quarry.
• OCT. 4, 1915: President Woodrow Wilson signs proclamation establishing 80 acres surrounding the Dinosaur Quarry as Dinosaur National Monument.
• AUG. 19-SEPT. 2, 1928: Al Birch, Charles Mace, Frederick Dunham and Burt Moritz Jr. complete the Denver Post Expedition through the Yampa Canyon, publishing the first photos and stories about the gorge.
• JUNE 1929: Bus Hatch of Utah guides the first recreational trip through present-day Dinosaur National Monument, launching Colorado’s whitewater tourism industry.
• JULY 14, 1938: President Franklin D. Roosevelt signs a proclamation expanding the monument by approximately 200,000 acres to include the canyons of the Green and Yampa rivers.
• JULY 1947: U.S. Department of Reclamation first proposes damming the Green River just below its confluence with the Yampa at Echo Park and at Split Mountain, 25 miles downstream.
• APRIL 11, 1956: President Dwight Eisenhower signs the Upper Colorado River Storage Project into law, including a provision killing the dam proposal in Echo Park while approving the Flaming Gorge dam upstream and the Glen Canyon dam downstream on the Colorado River.
• 1956 and 1957: Congressional bills seeking national park status for Dinosaur National Monument are defeated or abandoned because of political fallout from the storage project.
• JUNE 1, 1958: Dinosaur Quarry visitor center opens to the public.
• 1965: The Monument Headquarters Visitor Center and Harpers Corner tour road are opened.
• JUNE 1965: After more than two weeks of steady rain, Warm Springs Draw in the Yampa Canyon floods and creates Warm Springs Rapids on the Yampa River, considered the largest in the monument. A day after the rapids form, Les Oldham is killed while guiding a troop of Boy Scouts from Denver.
• DECEMBER 2006: Northern Colorado Water Conservancy District announces a prospective $4 billion dam project on the Yampa River near Cross Mountain Gorge upstream of the monument.
• JULY 2006: Dinosaur Quarry visitor center is closed because of safety hazards. The National Park Service hopes to reopen the facility within four years.
