Going clockwise, it starts out as a rolling, swooping single track. Fir needles, a few roots, nice. After you walk your bike two hundred yards on the Pacific Crest Trail, the trail changes to more rocky single track with steeper pitches. You cross a few roads, but there isn't much traffic up there. The part around Clackamas Lake is pretty easy--very dusty in late summer. The latter part of the ride on the east side of Timothy Lake has a few technical spots, but nothing too serious. Come out on forest road 57, cross the dam, and you're done.
Park near the Timothy Lake Dam. $5 daily fee.
http://www.singletracks.com/item.php?c=1&i=8489