In addition to providing access to the East Face route of Grays Peak, the Horseshoe Basin trailhead also is a good starting point for accessing Mount Edwards via a variety of routes, as well as lesser known peaks such as McClellan Mountain and Argentine Peak via the Argentine Pass trail, and possibly even Ruby Mountain.
This trailhead is actually the starting point for several trails, since the west side of the Argentine Pass begins here as well, but more importantly, this is the point on the Peru Creek road where it ceases to be non-4WD friendly.
-Drive to Keystone on US 6.
-At the east end of Keystone, head towards the Montezuma Parking Lot, and pass it on your way west. This will end at a T-junction on Montezuma Road; turn right (south).
-NOTE: If so inclined, park at the Montezuma Parking Lot, and head into the village area to find an open year-round Starbucks. :)
-Follow Montezuma Road (paved) for 4.7 miles, and reach the Peru Creek junction on the left side of the road.
-Follow Peru Creek Road (dirt) for 5 miles and reach the unmarked trailhead.
With careful searching, the trailhead for Argentine Pass Trail can be seen, and there will be some rough parking spots available here (3 or so). If all of these parking spots are taken, you may have to drive back down Peru Creek Road for .3 miles to a larger parking area (that you passed on your left on the way to the trailhead.)
There are several campsites to be found along Peru Creek Road. Most of the road prior to the Chihuahua Gulch trailhead is on private land, but for the moment, camping is permitted, but to ensure future camping is allowed, please try to leave the campsite in better condition than you found it. :)