Sugarloaf is far enough from the Bay Area to keep the crowds down. Visit during springtime to see the wildflowers in bloom, and the park generally green. Resembles a blast furnace in the summer.
The park used to have primitive campsites, but I have heard they've been developed since I was last there. You can expect to find toilets and potable water available in the campground, plus tables and fire pits or stoves at each campsite.
From Highway 101 near Santa Rosa, take Highway 12 eastward to Adobe Canyon Road. Follow Adobe Canyon Road northward to the park.
USGS 7.5' Topo Maps
Sugarloaf Ridge State Park