Mount Jefferson Wilderness, Wilderness area in the Cascade Range, Oregon, United States.

Mount Jefferson Wilderness encompasses over 111,000 acres across three Oregon counties, featuring alpine meadows, rocky slopes, numerous lakes, and the towering 10,497-foot Mount Jefferson peak with five surrounding glaciers.

Designated as a wilderness area in 1968 through Public Law 90-548, Mount Jefferson Wilderness became part of the National Wilderness Preservation System with additional protections added through the 1984 Oregon Wilderness Act.

The wilderness lies within the Willamette and Deschutes National Forests and is managed by the U.S. Forest Service. It is the second most visited wilderness area in Oregon after the Three Sisters Wilderness, drawing hikers, climbers and cross-country skiers to its 190 miles of trails.

Visitors can explore approximately 190 miles of trails including sections of the Pacific Crest Trail, but must follow Leave No Trace principles and carry topographic maps for safe navigation in this remote wilderness.

Roughly half the lakes in the Mount Jefferson Wilderness hold rainbow trout, and Marion Lake is a breeding site for amphibians such as the rough-skinned newt. Between Three Fingered Jack and North Sister, cinder cones cover 85 square miles among recent basalt lava fields.