Proceed to the southeast side of Pete's Hole Reservoir. You'll find the trailhead just beyond a picnic table. Prepare for 6.8 miles of delightful singletrack, well worth riding if you're in the area (Price, Ephraim, or I-70 between Salina and Green River).
This trail is part of the Great Western Trail (Utah Section) and is signed accordingly, with markers resembling those for the Pacific Crest Trail. (See expeditionutah.com/featured...
) It has the high-elevation feel of some of the trails around Gunnison and Crested Butte.
An intermediate mountain biker can ride the first couple of miles in 10-20 minutes. That section is mostly flowy and quite level by cross-country trail standards. It gets harder at that point, though, so only advanced riders should plan to do the whole thing in 45 minutes. About a third of the way in, one starts to encounter rooty and a few rocky sections, short power climbs, and short partly overgrown segments. The Forest Service says it maintains this trail but as of this writing hadn't gotten to it for 2014, so there were some tree trunks lying across the trail.
In about four miles, near Josephite Point, one turns south. At this point the trail may become hard to follow, so look for the Great Western Trail marker posts to guide you. The trail shows evidence of being used for horses or packstock in this area; it's heavily divoted in places.
There's a short final climb that takes one to Mary's Lake. When you reach the Mary's Lake trailhead, it's about 500 feet to the lake itself. Beware of mosquitoes at the otherwise pleasant lake.