Sonoma Wings is working on this issue. We'll let you know if there is any change. The field to the north east of the crossroads in Stonyford is also commonly used - about 9 miles from launch, if you don't make it out to the reservoir. If you are really sinking out badly, you can set down in one of four round looking fields north of the visitors center. You have to walk a bit to get out of these fields.
Most folks use the one nearest the road.
There is also an LZ in the large valley south of the mountain, although it is pretty much a long glide unless you sink out in front of Snow Mountain. Along the south side of the road going into Stonyford is the large Flying S Ranch. Click here for a map. This ranch starts at the foothills and proceeds all the way into Stonyford. The owner of this field has given his OK for occasional landings.