Island Park Caldera

Island Park Caldera is a vast volcanic depression that spans across Idaho and Wyoming, forming a large sunken area in the landscape. The terrain includes diverse habitats with lakes, rivers, forests, and open meadows that together create one continuous expanse.

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.

Nested within the larger caldera lies a smaller volcanic depression called Henry's Fork Caldera, which formed from an earlier eruption. This layered structure shows how complex volcanic forces have shaped the region across millions of years.

Location: Idaho

Location: Wyoming

Elevation above the sea: 2,805 m

GPS coordinates: 44.33000,-111.33000

Latest update: January 1, 2026 10:02