My two favorites are Boggs Mountain near Calistoga; great singletrack and a few loops to choose from. The second is on the North Shore of Lake Tahoe; the trailhead is near Boreal Ski Resort, called Hole in the Ground. It's best if you can drop a car at the end--17 miles of great climbs and incredible singletrack. Both are definitely worth the drive.

Depend on where you live,but I would suggest "Henry Coe Park" There are two entrtances to the park. One is in gilroy, and the other is in morgan hill. I'm talking about gilroy side. There are all kinds of rides out there and as a expert rider, I can definitely say that this place is pretty awesome! You need to be at least an intermediate rider to be able to ride at this park other wise you'll end up walking all the way. There are all kinds of single track and creek crossing, you get to see wild lives like pigs and coyote! Thank god I've never seen A mountain lion though. To get there, take 101. Get off at Leavesly Rd exit. If you are coming from North, take a left at the exit. From south, go right. Pass through the outlet mall, stay on leavesly rd. You'll also see the brown sign says, "Henry coe Park" or,"Gilroy hot spring." Take a left on roop,or loop. Then right on new rd.(Could be new is first and then roop. I just know how to get there so I don't usually pay attention to those no more!) There will be the signs as well. Then at the first Y-junction,go right. Don't go to cayote creek park. Then you;ll hit another y-junction. go left and over the cettle guard. After that, just stay on the road until you see the big parking lot with the "Henry Coe state park" sign.You can either park your car there or keep on driving until you see the bridge where is not too far from that point. A lot of the bikers parks by the bridge too but spaces are limited.
My favorite ride there is "Anza trail." As I mentioned earlier,there are all kinds of ride up there but the park is so huge,you might get lost too. So Make sure to get a goos map from the ranger. If you want to stay on the fire rd, that is also possible. But you should try the single track though. They are on the left hand side as you go up the fire rd.
Just make sure that you know which way you are going and you shouldn't have any problem. Turn around if you are not so sure about which way to go. If you would like to know more about this ride,let me know! I'll get back to you at here!
Always make sure that you have a repair kit and plenty od water and food. Be Prepared!!!!!
You don't have to be too worried but I just wanted to make sure your safety!!!!
The another good ride in nor cal is in santa cruz.Stop by the bike shop and they'll gladly help you out!