Mount Bailey Trail Via Diamond Lake is a 11.2 mile moderately trafficked out and back trail located near Idleyld Park, Oregon that features beautiful wild flowers and is rated as moderate. The trail offers a number of activity options and is accessible from March until October.
There are two separate starting point to get to the summit of Mt Bailey: a lower trailhead (10.5 miles out and back) and an upper trailhead (about 5 miles out and back). I hiked from the lower trailhead a short .4 miles from the Diamond Lake South Shore on NFR 300 (left turn from the paved Diamond Lake Loop. The access to the lower trailhead does not require a high-clearance vehicle. I cannot vouch for the access to the upper trailhead on NFR 380.
The 2+ miles between the lower and upper trailhead are easy to navigate, on a well maintained, forested and nicely graded trail. The last .5 miles are essentially flat on a sandy plateau. After crossing NRF 380, the trail is noticeably steeper but still shaded as the treeline is only reached shortly before the false summit. There are a few steep sections going straight up the slope but most of the trail is still well maintained with not too many rocks or roots. To wit the fact that trail runners are using this trail all the way up to the summit. On the way up to the tree line, a few good views of Diamond Lake and Thielsen peak are opening up.
The trail finally reaches the treeline a bit under the first key feature of the hike: a crated just below the false summit which, early in September, still has tong of snow on its South edge. At that point, the views are fully opened to the South with Mt Scott and Mt McLoughlin in plain sight. After rounding the crater, the trails switches-back to the false summit and the first sweeping views East and West as well as the spine to the true summit to the North.
The spine leading to the summit is the only section of the hike that is a bit 'technical". A few "gendarmes" stand on the way and the trail follows their Western (left) edge at the top of steep and long scree fields. A bit of caution here and there in that section can avoid bad surprises. This is also where the second main feature of the hike awaits you: a window in the "gendarme" face that frames Thielsen and Diamond Lake in dramatic fashion.
Past the last gendarme, the trail gently edges up toward the true summit (no marker, no summit register as of 9/2016). Continue a short .1 mile further and slightly down and get an unobstructed view of Diamond Lake and Thielsen. The horizon was a bit cloudy to the North when I was at the summit, but on a good day you should be able to see Diamond Peak and the Sisters.
Bottom line: if you can start from the upper trailhead, climbing Mt Bailey is a must from the efforts to rewards ratio.