The Bona-Churchill massif in the St. Elias Mountains has a 2.7 x 4.2 km summit caldera which was the source of the White River Ash, produced by two of the largest explosive eruptions in North America during the past 2,000 years (McGimsey et al., 1992). The summit of Mount Bona lies 4 km across a high saddle from the younger Churchill. The source vent of the widespread bi-lobate White River Ash deposit, which covers more than 340,000 km2 of eastern Alaska and NW Canada, was initially thought to be a pumice mound that is mostly buried beneath the Klutlan Glacier NE of Churchill volcano. Later work revealed thick young pumice deposits along the caldera rim that are mineralogically and chemically similar to the White River Ash deposits.