Find out how you can get out and enjoy Diamond Peak, a true Oregon gem. An experienced REI staff member will share first-hand accounts to help you feel more comfortable accessing this backcountry destination on. Diamond Peak Wilderness straddles the Cascade Mountains. Great glaciers carved the large volcanic peak and when they receded, the bulk of the mountain remained, with snowfields near the summit and dozens of small lakes surrounding the peak. Diamond Peak Wilderness area covers 52,611 total acres. Lakes from one to 28 acres in size dot the landscape. Approximately 14 miles of the Pacific Crest National Scenic Trail pass through this wilderness. Another 38 miles of trail, including the 10-mile Diamond Peak Trail, stretches the length of the west side of the peak.