18,000 B.C. Earliest evidence of humans in Wyoming.

11,000 B.C. Earliest evidence of humans in Montana.

A.D. 1620s Arrival of the Plains Indians.

A.D. 1807 John Colter explores the Yellowstone area, going as far south as Jackson Hole.

1867 The Union Pacific Railroad enters Wyoming.

1869 A party led by David Folsom undertakes the first modern exploration of Yellowstone.

1871 The Hayden Expedition surveys Yellowstone.

1872 Yellowstone is established as the nation's first national park.

1876 Warriors from the Sioux, Lakota, and Cheyenne tribes defeat General George A. Custer and his troops at the Battle of the Little Bighorn. (Montana)

1877 Chief Joseph of the Nez Perce tribe surrenders to U.S. soldiers in the Bear Paw Mountains after a flight that took his tribe though Yellowstone.

1883 The Northern Pacific Railroad crosses Montana.

1889 Montana, on November 8, becomes the 41st state in the Union.

1890 Wyoming becomes the nation's 44th state.

1988 Five fires break out around Yellowstone, blackening approximately one-third of the park.

1995 Gray wolves are reintroduced into Yellowstone National Park.

2007 The U.S. Forest Service removes the Greater Yellowstone grizzly bear population from the threatened species list.

2007-08 Due to brucellosis fears, over 1,500 Yellowstone bison are killed as they cross into Montana.

2008 The gray wolf population in the Northern Rockies hits 1,600; the species is no longer listed as endangered.

2009 Montana has its first legal wolf-hunting season since reintroduction in 1995.

2010 A court ruling returns the grizzly bear to the threatened species list.

2010 A court ruling returns the gray wolf to the endangered species list.

2011 The U.S. Congress returns gray wolf management to the states, effectively delisting the species again in Wyoming and Montana.

2011 A grizzly bear kills a visitor near the Grand Canyon of the Yellowstone, the first bear-related fatality in the park in over 20 years.

2016 A young man dies after falling into an off-trail spring, and several visitors are fined for walking into Grand Prismatic Hot Spring, then posting the crime online.

2017 The U.S. Fish and Wildlife Service takes the Yellowstone grizzly bear population off the threatened species list.

2018 A court ruling returns Yellowstone grizzlies to the threatened species list.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.