From the trailhead (image left), follow the Mesa Trail to the Homestead Trail which branches left off of the Mesa Trail approximately 0.1 miles after leaving the trailhead. Follow the Homestead Trail west-northwest. After 0.9 miles the Homestead Trail merges with the Towhee Trail. Continue heading west on the Towhee Trail. After 0.2 miles the Towhee Trail merges with a segment of the Mesa Trail.
Continue heading west on the Mesa Trail for 0.3 miles until an unmarked trail branches off of the Mesa Trail heading south (image left). This trail is called the Old Mesa Trail. Follow the Old Mesa Trail south.
Shortly after heading south on the Old Mesa Trail, the trail will break out of the trees into nice grassland. Shirttail Peak can be seen to the southwest (image left).
From here the trail continues to the south downhill. Follow the Old Mesa Trail south for a total of 0.5 miles to where you can leave the trail and head west up a gully that is immediately north of Shirttail Peak. This gully can be seen in the center of the image to the left. Bushwhack up this gully to its terminus near the top of the ridge. From here head southeast to the summit of Shirttail Peak. Reaching the summit requires a few class 2+ moves.