The Huckleberry Ridge Tuff is a tuff

Tuff

Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...

 formation created by the Huckleberry Ridge eruption that formed the Island Park Caldera

Island Park Caldera

The volcanic feature commonly called the Island Park Caldera in the states of Idaho and Wyoming, U.S., is actually two calderas, one nested inside the other. The Island Park Caldera is the older and much larger caldera, with approximate dimensions of 58 miles by 40 miles...

 that lies partially in Yellowstone Park, Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 and stretches westward into Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

 into a region known as Island Park

Island Park, Idaho

Island Park is a city in Fremont County, Idaho, United States. The city's population was 215 at the 2000 census. The city was incorporated by owners of the many lodges and resorts along U.S. Route 20 in 1947, primarily to circumvent Idaho's liquor laws that prohibited the sale of liquor outside of...

. This eruption of 2,500 km³ of material is thought to be the largest known eruption in the Yellowstone Hotspot's history and the third largest known explosive volcanic eruption in Earth's history, next to the Toba eruption and the Fish Canyon eruption that formed La Garita Caldera

La Garita Caldera

La Garita Caldera is a large volcanic caldera located in the San Juan volcanic field in the San Juan Mountains near the town of Creede in southwestern Colorado, United States. It lies to the west of the town of La Garita, Colorado...

 in Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

. This eruption, 2.1 million years ago, is the third most recent large caldera forming eruption from the Yellowstone hotspot

Yellowstone hotspot

The Yellowstone hotspot, also referred to as the Snake River Plain-Yellowstone hotspot, is a volcanic hotspot responsible for large scale volcanism in Oregon, Nevada, Idaho, and Wyoming, United States. It created the eastern Snake River Plain through a succession of caldera forming eruptions...

. It was followed by the Mesa Falls Tuff

Mesa Falls Tuff

The Mesa Falls Tuff is a tuff formation created by the Mesa Falls eruption that formed the Henry's Fork Caldera that is located in Idaho west of Yellowstone Park. It is the second most recent caldera forming eruption from the Yellowstone hotspot and ejected of 280 km³ of material...

 and the Lava Creek Tuff

Lava Creek Tuff

Lava Creek Tuff is a tuff formation, in Wyoming, created when the Yellowstone Caldera erupted about 640,000 years ago.The Lava Creek Tuff distributed in a radial pattern around the caldera and is formed of of ash in pyroclastic flows....

eruptions respectively.