In terms of fun places to ride near San Jose, CA:
I like riding at Almaden Quicksilver County Park. If you drive around to the south end of the park (to the little town of New Almaden), there is a parking lot for mountain bikers. You have to walk up a big hill (about a ~700’ elevation rise over about a mile). But, once you are up there, there is a nice ~10-mile loop. Then, a fun ride all they way down the hill.
I also enjoy Coyote Hills Regional Park. The “hills” are only about 200’ tall. But, some pretty steep down hills. This is where my brakes heat up. You can ride all over the park or onto the levees into the SF Bay. Super mellow, way less extreme than China Camp. I love riding here before work. Probably my favorite spot.
Another place that is mellow and fun to ride before work is Bedwell Bayfront Park, near Facebook. If you try to ride every trail in this little park, you can get a ~10-mile ride in. Just watch out for skunks. Fun little hills. GREAT place for beginners just starting to get off road on a muni.
Finally, near Google there is a great ~10-mile loop (pretty flat). Park your car on Terminal Blvd (zip code 94043) at the entrance to the Palo Alto Baylands Nature Preserve Trail. Ride a few hundred feet out to Adobe Creek Loop Trail and take a left to get out to the 101 (yes, I’m from So Cal), once you hit the 101 ride north along the 101 to the Baylands Athletic Center (may need to look on a map). From here jump on the San Francisquito Creek Trail and go around the Palo Alto airport. This gets you to Embarcadero Rd which you can then ride to get back on the Adobe Creek Loop Trail but keep going around the loop, past The Bowl (of course, ride into the Bowl!). And then back to where you began. It’s a nice 10-mile loop if you also ride up onto Byxbee Park. The cool thing about this ride is that when you are out on the marshes, it’s all single track (really pretty along the water). Totally flat, but miles of single track with little jumps. Love this ride. (All of these directions are from looking on Google Maps).
One more fun ride. If you park on Terminal Blvd (zip code 94043) but go South (or East) on the trails, there several fun paths/trails around Google and Shoreline Amphitheatre. Be sure to hit Boy Point Regional Shoreline Overlook, Crittenden Hill, or take the Bay Trail around the back side of Nasa Ames to Sunnyvale where you can hook up with Aliviso Slough Trail and other fun trails that lead out onto the SF Bay levees.