Boggs Mountain (Peak approx. 38.814566,-122.690506, elev. 3750 ft.) is seven miles northwest of Middletown and eight miles south of Clear Lake in Lake County, California. It is well known by mountain bikers for its numerous excellent single track trails which are maintained year-round by a nonprofit organization, Friends of Boggs Mountain; there are also prepared trails designated for hiking. Interestingly, there is also a shooting range on the property open to the public, although it is a short-distance range appropriate mostly for pistol shooting.
Besides trail maintenance by Friends, the property overall is maintained by the California Department of Forestry and Fire Protection. They acquired the 3,493 acre property from the Calso company in 1949, and it is available for public use year-round. There are a couple of big bike races in Boggs every year; Bike Monkey Magazine just had (effectively) their fourth anniversary race there on March 28, 2009, and there are Global Biorhythms races coming this June and July.
Boggs is right next to and a little shorter than Cobb Mountain. Cobb is pretty heavily populated by comparison since pretty much all of Boggs was logged. Cobb is quite a bit steeper on average, and has a lot more water on it, mostly in the form of numerous springs. That makes it a better place to live, but not such an excellent location for mountain biking or even hiking. From Boggs you could also get into Harbin Hot Springs via the upper trails, although this is unsurprisingly a practice they frown upon if you're not a resident. (Cobb, on the other hand, gets you into thousands of acres of land held/managed by Calpine Geothermal Power, and from there into even more land "managed" by the federal Bureau of Land Management.) But Boggs' logging history is precisely what makes it so attractive for recreational use, because the land is relatively clear. Northern California seems sometimes to have more poison oak than any other plant whether you measure numerically or by total mass, but Boggs is relatively clear in general even if you venture off of the trails.
I'm living in Lake County and recently got my first All-Mountain Bike, and so I'm blessed to have this resource available. For an out-of-shape, beginning rider like myself the fire roads are a blessing, but for an experienced rider it's entirely possible to ride up and down without them. There's also the Calso Camp(ground) about halfway up the mountain from the initial parking lot. The owner of the Calso Water Company owned this and another property in this county, and had a camp here, but the water was bottled elsewhere. Many downhill riders will use multiple vehicles and portage the bikes to the top, then come back for the car later.
To reach Boggs Mountain, take CA Highway 175 towards Cobb from Kelseyville or Middletown and take Forestry Rd. Many mountain bikers recommend "Gail's Trail" (for which I can vouch) or the "Creek Trail". There is an "interpretive trail" mostly for hiking, which features signs describing aspects of the local terrain, mostly sizable flora.