We've got it all here. The Marin Headlands is where the MTB was born. The road riding around here is also fantastic. Honestly, if I were you, I'd just figure out what type of bike you feel like riding and then figure out your rides afterwards. You aren't going to go wrong with any choice. I'm not a CX guy, so I don't know much about that, but road/MTB you will not be disappointed either way.