Island Park Caldera, Volcanic caldera in Idaho and Wyoming, United States.

Island Park Caldera is an oval volcanic depression about 80 by 65 km across, lying in Idaho and Wyoming and reaching into Yellowstone National Park. Its western rim is shared with the smaller Henry's Fork Caldera nested inside it. The floor holds forests, large springs, streams, lakes, ponds and marshes, and the Teton Range peaks are visible to the southeast.

The caldera formed roughly 2.1 million years ago from a massive volcanic eruption that caused the Earth's crust to collapse inward. Since then, water and erosion have shaped the basin, creating the lakes and rivers that exist today.

Harriman State Park within the caldera preserves the memory of early Union Pacific Railroad investors who transformed the land into a private retreat in the early 1900s. Visitors can still see traces of this era in the buildings and how the land is used today.

The area offers year-round activities including snowmobiling, fishing, cross-country skiing, and wildlife viewing. Visitors should prepare for changing weather conditions and consider the season when planning their visit.

The Henry's Fork Caldera nested inside it is younger, not older: it formed 1.3 million years ago in an eruption of more than 280 km³ that produced the Mesa Falls Tuff. The two calderas share the same rim on their western sides, while the older Island Park rim reaches far into Yellowstone National Park.