Yellowstone National Park, Wyoming, Idaho, Montana, United States

By 1915, 1,000 automobiles per year were entering the park, resulting in conflicts with horses and horse driven transportation. In subsequent years horse travel on roads was eventually prohibited. Between 1933 and 1941, the Civilian Conservation Corps built the majority of the early visitor centers, campgrounds and the current system of park roads. During World War II, staffing and visitation both decreased, and many facilities fell into disrepair. By the 1950s, visitation increased tremendously in Yellowstone and other national parks. To accommodate the increased visitation, park officials implemented Mission 66, an effort to modernize and expand park service facilities. Planned to be completed by 1966, in honor of the 50th anniversary of the founding of the National Park Service, Mission 66 construction diverged from the traditional log cabin style with design features of a modern style. During the late 1980s, most construction styles in Yellowstone reverted back to the more traditional designs. After the enormous forest fires of 1988 damaged much of Grant Village, structures there were rebuilt in the traditional style. The visitor center at Canyon Village, which opened in 2006, incorporates a more traditional design as well.
The 1959 Yellowstone earthquake just west of Yellowstone at Hebgen Lake damaged roads and some structures in the park. In the northwest section of the park, new geysers were found, and many existing hot springs became turbid. It was the most powerful earthquake to hit the region in recorded history. In 1963, after several years of public controversy regarding the forced reduction of the elk population in Yellowstone, United States Secretary of the Interior Stewart Udall appointed an advisory board to collect scientific data to inform future wildlife management of the national parks. In a paper known as the Leopold Report, the committee observed that culling programs at other national parks had been ineffective, and recommended management of Yellowstone's elk population.
The wildfires during the summer of 1988 were the largest in the history of the park. Approximately 793,880 acres (321,272 ha; 1,240 sq mi) or 36% of the parkland was impacted by the fires, leading to a systematic reevaluation of fire management policies. The fire season of 1988 was considered normal until a combination of drought and heat by mid-July contributed to an extreme fire danger. On "Black Saturday," August 20, 1988, strong winds expanded the fires rapidly, and more than 150,000 acres (61,000 ha; 230 sq mi) burned.
The expansive cultural history of the park has been documented by the 1,000 archeological sites that have been discovered. The park has 1,106 historic structures and features, and of these Obsidian Cliff and five buildings have been designated National Historic Landmarks. Yellowstone was designated an International Biosphere Reserve on October 26, 1976, and a United Nations World Heritage Site on September 8, 1978.