Waldo Mountain is a 6,361-foot summit in Oregon in the Waldo Lake Wilderness of the Willamette National Forest, near Waldo Lake in the central Cascades. An extinct shield volcano, it is part of the Diamond Peak chain along with nearby Cupit Mary Mountain, and its broad, forested shape reflects that volcanic origin rather than the steeper form common to many Cascade peaks. The mountain and adjacent lake were named for Oregon jurist John B. Waldo. At the summit, the Waldo Mountain Fire Lookout reflects the mountain’s continuing importance as a vantage point over the surrounding wilderness.