Near the beginning of the Horn Creek Trail, there should be signage for the Rainbow Trail. From the Horn Creek TH, follow the trail for about 1/2? mile or so to a four-way junction. Take the right fork to intersect the Rainbow Trail, in the direction of Dry Creek. Overall distance is perhaps 3/4 mile to here. Follow the Rainbow Trail north for another third of a mile until it intersects the Dry Creek Trail. The climb for Horn Peak begins at this intersection.
At-large camping is available a little beyond the trail head where the road ends in a loop. At our last visit in 2000, there were no facilities at all here. Remember that if you camp here, you are very close to the Horn Creek Ranch so your campsite is not very private and private property is close by.