1959 The Organic Act of 1916 establishes the National Park Service
A magnitude 7.5 earthquake strikes on August 17, killing 28 campers in Gallatin National Forest and affecting the park’s geysers and hot springs
1920 The mass production of automobiles made YNP readily accessible, increasing visitation drastically from its opening. In 1920 about 5,000 automobiles enter the park
1929 President Hoover signs first law changing Yellowstone National Park’s boundary and creates Grand Teton National Park
1966 The thermophile Thermus aquatics is discovered in a hot spring
New bear management plans begin, which include closing open-pit dumps in the park
The famous Beartooth Highway is built, allowing visitors to enter Yellowstone from Red Lodge, Montana, via Cooke City and Silver Gate
2016
1971 Overnight winter lodging opens across the park
On February 9, the all-time lowest temperature in Yellowstone is recorded at -66º F at the Riverside Station
1955 Mission 66 is initiated in a massive effort to expand Yellowstone’s roads and trails, as well as visitor and employee facilities
1974 Fishing is prohibited from Fishing Bridge in order to protect spawning areas of the native cutthroat trout
1933
Yellowstone recieves one million visitors
Scientists release the Leopold Report, which established the framework for park management still used today throughout the National Park system
1970
1930
1948
1963
1975 Grizzly bears are listed as a threatened species in the lower 48 states