The trailhead for McCullough Gulch uses the same directions as for Quandary Peak, initially. If coming from Breckenridge on SH 9, drive south from the center of town approximately 8 miles where you turn right (west) onto "Blue Lakes Road #850.
If coming from Hoosier Pass on SH 9, drive north from the summit of the pass just over 2 miles to the left turn (west) onto Blue Lakes Road #850.
Once on CR 850, drive past the large, day-use parking lot and make a right turn (north) onto CR 851. This is the same road that takes you to the well-used east ridge approach for Quandary. If arriving here on a summer weekend, drive past the multitude of cars parked along the road left by 14er baggers, and continue north, to NW for 1.7 mile to an intersection. The trailhead coordinates provided are for this intersection. If you can find a place to park, do so nearby to begin your hike. The road to this point is typically driveble by passenger vehicles. If no parking is readily available, take the left fork and you may be able to drive another .5 mile to a locked gate and a place where you can park at 11,090 ft. at these coordinates: N 39° 24' 03.99" W 106° 04' 45.23". Alternately, you can also take the right fork and drive down to the creek and park.
Some at-large camping may be available in the area of the trailheads identified, especially down by McCullough Creek. But if arriving on a summer weekend, most any decent spot will likely be taken. There are no National Forest campgrounds in the immediate vicinity. For campgrounds located near Dillon Res., try this site for more information: http://www.townofdillon.com/visit/camping-info.