Diamond Peak, Shield volcano in Klamath County, Oregon, US.

Diamond Peak is a shield volcano on the Klamath–Lane county line in central Oregon, reaching 8,748 feet near Willamette Pass. It has two overlapping cones, the lower northern one older, built of palagonitized rock, basaltic andesite cinders and thin lava flows. Glaciers have cut cirques into its slopes.

William Macy and John Diamond made the first recorded ascent in July 1852 while surveying for construction of the Free Emigrant Road. Their climb was part of the early exploration efforts of the region.

The mountain is named for pioneer John Diamond, who settled near Coburg in September 1847 and made the first recorded ascent with William Macy in July 1852. The 52,611-acre Diamond Peak Wilderness is jointly managed by the Willamette and Deschutes national forests and holds 14 miles of the Pacific Crest Trail plus 38 miles of other trails.

The Diamond Peak Wilderness is largely inaccessible by road in winter; the northern side can be reached from Gold Lake Sno-Park on Oregon Route 58. The wilderness contains 14 miles (23 km) of the Pacific Crest Trail and 38 miles (61 km) of additional trails. The mountain lies 62 miles (100 km) southeast of Eugene and 64 miles (103 km) southwest of Bend.

The mountain bears visible traces of glacial erosion with distinct cirques and moraines showing the extent of past ice movements. These glacial features remain clearly visible in the landscape today.