Huckleberry Ridge Tuff, Volcanic tuff formation in Yellowstone National Park, Wyoming.

Huckleberry Ridge Tuff is a tuff formation left by the Huckleberry Ridge eruption 2.1 million years ago, which formed the Island Park Caldera, partly inside Yellowstone National Park in Wyoming and reaching west into Idaho's Island Park region. The eruption expelled about 2,450 cubic kilometres of material, and it likely occurred in three phases separated by decades.

The deposit formed around 2.1 million years ago during a huge eruption in the Yellowstone area that released more than 2,400 cubic kilometers (580 cubic miles) of material. This eruption was one of the largest in Earth history and shaped the northwestern North American landscape for millennia.

The name comes from Huckleberry Ridge in Montana, where geologists first documented the formation. Today, hikers along the Gardner River see the deposits as gray and pinkish rock layers in the canyon walls.

The tuff lies partly in Yellowstone National Park, Wyoming, and extends west into Idaho's Island Park region. The mapped ash bed reaches across the central United States, so exposures are scattered rather than concentrated at one site. Check road and trail access before setting out, and carry water on exposed ground.

Geologists recognize three separate eruption phases in the formation, each with its own mineral makeup and grain size. Some sections contain tiny quartz and feldspar crystals that sparkle in sunlight.