If coming from either the Front Range or the Western Slope, drive to Gunnison. From Gunnison, drive north on SH135 to Crested Butte. Stay on this main road as it enters the town, driving on through a major intersection with stop signs. Continue north on what becomes CR317 to the base of the ski area which is the Town of Mt. Crested Butte. Continue on the same road and a little after the main village and passing numerous condos, etc., the road will change over to a graded dirt road. During summer months, water trucks douse the road to help hold down the dust. Driving this road just after one of those trucks has gone through can change the road to a squishy, muddy mess, briefly. Continue on CR317 to the site of Gothic which has a small but nice visitor center where you can inquire about parking regulations, hiking and biking trails and the research that is conducted in this area. During summer months daylight hours, this road is heavily travelled and parking is restricted to designated areas.
Continue driving NW past Gothic another 2.5 miles to where the road for Rustler Gulch heads off to the right (north). This is FR317.2B on CalTopo. The Gunnison National Forest map does not really show this road. This road is less than a half mile past the "Gothic Campground." If in a passenger car, park in the vicinity of the turnoff. There's no sense in trying to get any further without 4WD. If you do have 4WD and the East River is not in high stage runoff, drive on down the rocky stretch through some close, tall willows and ford the river. Once across, the road will head steeply uphill for .7 mile to an intersection where you'll see a gate across the road that heads off to the right. Park here if there's any room to do so. Two or three vehicles might be able to fit in off the road just enough to let other vehicles by. Coordinates for this spot are: N38° 59' 57.31" W107° 00' 11.05". There's a stand of tall willows here.
Right after where FR317.2B crosses the East River, there's an area that can accommodate a limited number of vehicles and some primitive camping right off the road. Then further up the road a short distance is another primitive spot that could accommodate a single vehicle on the right.
For camping further away, try the Gothic Campground about a half mile before FR317.2B or some other primitive spots either back toward Gothic or further up the main valley of the East River.