For this "approach" there are two possible start points. If in a passenger car, the start will be where FR317.2B turns off of FR317 to cross the East River. You will then need to walk up FR317.2B to the trailhead coordinates. If you have 4WD, the start will be about a mile up after having forded the East River at the trailhead coordinates provided. There's a fence line and gate across the road/trail there.
From the gate, walk north on the old road bed. In July, you'll enjoy a plethora of wildflowers that will distract you from the hiking. Heading up the well-used trail, walk through an open meadow before entering a forested section with a considerable amount of bog, exacerbated by the horses that pass through regularly. Gingerly walk through, trying not to get too muddy this early into the backpack and continued on into open, flower-filled meadows that prompted us to frequently stop and take photos. This was just a taste of what awaits in upper Rustler. In short order, you'll come to a creek crossing that probably will require boot removal. However, a trail heading off to the right along the creek into the woods and willows goes to a place where you might be able to gingerly cross on some small logs and get across the creek. Once across, this side trail continues and eventually leads back to the main trail, but not before taking you through an incredible meadow of more wildflowers where you may want to spend even more time taking photos.
From this meadow, the open trail continues north and then begins to turn east into the upper basin. Continue up to where the trail has decidedly turned east and stop at a place where the creek, not too far below, cascades over some rock outcrops. Walk down and hop across the creek and hike up into a stand of trees and explore around. There was a faint game trail through here and a lot of fallen timber. Head upward and eastward through the timber. Near to where you exit the timber on the east side is a campsite, just the right size for two tents, with an old fallen log for cooking and eating and an old fire ring. See our approximate coordinates. This makes an excellent base camp for the six 13er summits you can access from this valley and is out of the way of the day hiking foot traffic that frequents this valley. A game trail of sorts leads east from the campsite, then turns north through lower willows back down to the creek for an easy crossing and to regain the main trail.
The upper basin of Rustler Gulch is so verdant and filled with wildflowers, you'll not likely find any campsite unless you want to trod down a bunch of flowers. The camp location described above is the only really decent campsite we found that would do minimal damage to the abundant wildflowers.