Diamond Peak stands above the Willamette Pass area of Oregon about 50 miles southwest of Bend. It's a little further west than the other peaks in the Cascade Range which accounts for high snowfalls and a few glacial remnants near the peak. It's reachable by several trails and is a popular ski mountaineering peak in winter with over 4000 skiable vertical feet. The summit was carved by glaciers and has many cirques. Pinnacled lava ridges connect the peaks. The glaciers left behind dozens of lakes around this peak as well.
While it is not one of the better-known Cascade Peaks, it's bulkiness can easily be seen from Mt. McLoughlin to Mt. Jefferson. It's not a difficult summit but it is a more remote peak and the trails can be long (up to 21 miles round trip from the Willamette Pass and around 40 miles round trip fom the west trails). The shortest and most popular path climbs the South Ridge and can be done in about half a day or so (10 to 12 miles).
The first ascent was in 1852 by John Diamond (namesake) and William Macy. It's a shield volcano unlike most of the other big classic Cascade peaks like Hood or Rainier which are stratovolcanoes. It does sit in an area with some other shield volcanoes such as Sawtooth Mountain and Cowhorn Mountain. Depending on the trail you take, the elevation gain can be from 2700 feet to 4100 feet.
The South Ridge is accessed through small gravel roads. See the South Ridge Route page for directions.
Another popular route is from the Willamette Pass area. The Pacific Crest Trail can be accessed from Highway 58 near the Pass. The PCT runs along the east side of the mountain and you can pick up a climbers trail to the summit. From Eugene, it's about 50 miles east on Highway 58 or, from the Bend area, you can take the Cascade Lakes Highway to Highway 58 and head west towards the Pass.
There are also many options to get into the Diamond Lakes Wilderness off Highway 58 including the Pengra Pass trailhead on Hwy 58 as well as Road 23, 2419, 5810 to the Yoran Trailhead, and Road 60. Marie Lake, Divide Lake and Rockpile Lake are popular basecamps for the climb.