Diamond Peak Loop is a 23 mile loop trail located near Crescent, OR and is rated as moderate. The trail is primarily used for hiking and is accessible from July until October.
I did this in June and there were quite a lot of mosquitoes. I was prepared with long sleeves, long pants, and a head net, so it wasn't too bad. The Diamond Peak area itself is quite good, though I'm hesitant to recommend the whole loop. The PCT side is very scenic as it's up at the treeline. The western side is forested for 12 plus miles between the Divide Lake trail and the Rockpile trail. I think doing the loop that stays completely on the eastern side (Yoran lake trail > PCT > Marie Lake > Diamond View Lake) would be nicer. The 3 stars are for the loop, not for the Diamond peak area, which is quite lovely.
Lots of beautiful scenery on this loop, and just the right length for a 3- or 4-day backpacking trip. Warning, though,... the mosquitoes were insanely horrible on this weekend that I hiked (July 3, 2014). I suspect it's just too early in the season since snowmelt. I would suggest doing this trip later in the year, perhaps September or October once the first freeze has eliminated the bugs. I left a can of bug spray on a log just before Diamond View Lake for anyone that decides they want to attempt this right now. We camped the first night a bit away from the late campsites due to bugs, but they were still horrible.
This is an amazing loop with lots to offer in the way of views and isolated mountain lakes. Trailhead is well-marked right across from Shelter Cove resort, "Yoran Lake Trail." (The loop is actually 27 miles, not counting little side trails you can take to nearby lakes). I recommend going counter-clockwise heading towards Yoran Lake first and taking at least 3 nights/4 days to complete in order to explore thoroughly and see some of the quick side trails. I did it in 2 nights/3 days and wished that I had more time. The trail is confusing around Bonnie's Lake and Yoran Lake and we lost it a couple times, but fairly easy to get back on track. Bring bug repellent and wait until at least the first freeze if possible before setting out if possible. Several logs blocking trail at places, but nothing too difficult to get over. This was my first overnight backing adventure and I am hooked now! I can't wait to go back and see some of the stuff I missed like Marie Lake, Divide Lake, and actually climbing to the top to see views of Mt. Shasta and Mt. Hood.