Take Interstate 5 north to Williams. Take Hwy 20 exit (1 mile past Williams exit) towards Upper Lake/Clear Lake. Proceed 60 miles to Upper Lake. Turn right on Mendenhall Ave (1 block past gas station on Main Street). Proceed 1 mile to Ranger Station, then turn left on Elk Mountain Rd (M1). Proceed 13.8 miles to Upper Deer Valley Rd (16N01). Turn right on Upper Deer Valley Rd (dirt road) and proceed 3.6 miles to the campground.
On Elk Mountain Rd you will pass the Middle Creek OHV Staging Area and Lower Deer Valley Rd. Note that the pavement above the Middle Creek Staging Area has a number of tight switch-backs; however, the road is smooth and wide with enough room to turn for trailers and motorhomes. Also, there is a fairly steep climb just after turning onto Upper Deer Valley Rd, so keep it in first gear at this point and give it plenty of gas, otherwise smooth sailing to the campground. Watch for TBSA signs. Elevation 3,700 feet; dry camping; one toilet; no fees. GPS readings: N 39E 15' 57.1068", W 122E 53' 01.8744".
Also note that the trails in this area are even better than those at Stonyford, plus there is a connecting corridor to Stonyford. Chas has extra maps of the area (Upper Lake Ranger District OHV Guide).