This oral history interview with Donald G. Onthank was conducted by Dorothy C. Rich and Dick F. LaPore at the Mazamas' club room in Portland, Oregon, in 1977. The interview was conducted in two sessions. Audiocassettes held at the Oregon Historical Society Research Library are duplicates of the original audiotape reels held by the Mazamas Library & Historical Collections in Portland, Oregon. Some of the audio on Cassette 2 was lost as the result of damage during duplication of the tape in 2001. In the first interview session, conducted on October 29, 1977, Onthank discusses his mountaineering experiences in the Cascade mountains of Oregon and Washington, and in the Columbia River Gorge, in the early 20th century. He describes climbing Mount Defiance, Mount Adams, Mount St. Helens, Glacier Peak, the Three Sisters, and Mount Jefferson. He speaks at length about hiking in the Columbia River Gorge, including trails leading to Mitchell Point, Tanner Butte, Wauna Point, and Larch Mountain. He talks about the equipment he used, and the people he climbed with. He also discusses how the trails he used have changed or disappeared over the 20th century. He shares his memories of climbing Mount Hood, including a climb in 1927 that resulted in the death of a Portland dentist, Dr. Stanton W. Stryker.

In the second interview session, conducted on November 12, 1977, Onthank continues to discuss his mountaineering experiences in the early 20th century. He speaks at length about climbing Mount Shasta in California, Mount Jefferson in Oregon, and Mount St. Helens, Mount Rainier, and Mount Olympus in Washington. He describes a time when he was injured in a fall while climbing, talks about people he climbed with, and discusses the equipment he used. He talks about his involvement with the Mazamas mountaineering club, including climbs he led, the organization's 50th anniversary celebration in 1944, and lodges owned by the Mazamas. He shares his thoughts on why climbing accidents have increased over the 20th century. He closes the interview by describing ways in which many trails have changed since he began climbing in the 1910s.