Diamond Peak summit is one of the best and most underrated summit hikes in the Oregon Cascade range. There are a few different routes up the mountain, but the route starting at Summit Lake is by far the easiest. Summit Lake has a small first come first serve campground if you want to spend the night after a long day of summiting. There is also a lot of primitive camping along the Pacific Crest Trail near Summit Lake, as well as near small ponds on the way to the Diamond Peak climber trail.
There is a large parking area across the road from Summit Lake campground where there is room for about 20 cars to park. Here you will see a trailhead sign and a sign for the Pacific Crest Trail. Southbound it is 13 miles to Windigo Pass, which is near Cowhorn Mountain. You will take the trail northbound for a total of 4.45 miles.