The Pumice Desert formed 7,700 years ago as part of the largest Cascade Range eruption in a million years. Mount Mazama first sent a huge column of ash skyward, followed by a series of glowing avalanches of gas-rich pumice rock that raced down the slopes on all sides. At the Pumice Desert the deposits buried a valley with material over 100 feet (30 meters) deep, thoroughly destroying all vegetation. Multiple challenges, including arid, nutrient-poor soil, temperature extremes, and a short growing season have kept forests from successfully recolonizing the area.