I think @maillotpois might be able to get better info than I have on Fairfield. I usually just drove through it and thought of it as the horror parking lot on I80. Generally, that area is geographically wonderful. Like Maillotpois said, its' relatively close to Tahoe which has excellent hiking, mtb and even road riding as well as other areas on the foothills. The UC Davis campus (not far from Fairfield) is a huge bike campus. Mt. Diablo is great for MTB as well as the hills between Fairfield and SF area. Levi Leiphenheiner road rides around Napa so you really can't go wrong there. A LOT of people tour down highway 1 along the coast as well as along the wine trails in and around Napa, Sonoma, Dry Creek etc. I do know you could road ride through small roads all the way to Antioch and along the river probably to SF.