About 2 miles from the City Creek parking lot up the Upper City Creek Trail you'll see Mushroom on the left. It doesn't have a trail sign but once you pass a fork with a unbridged creek crossing on the right you'll know you are almost there, about 100 yards more. This is a difficult trail with 3 decent hill climbs.
Traffic goes both ways and you'll overlay with Sulivan's for a little stretch. The trail eventually meets up with the end of the Upper City Creek Trail where it comes to the road. It is a mix of sage, junipers and trees.