The closest GDA or ECNL club to Walnut Creek is Lamorinda, which plays in GDA. I don't know too much about them, but they seem to play the right way, based off of the few games I've seen. I don't think they've been too successful in the GDA so far, but I have heard good things in the past about their DOC and how they develop players.Walnut Creek area......2006......thank you
The next closest would be Mustang SC, which plays in ECNL. They are one of the best clubs in NorCal. They have a great record of placing their players at the next level, and usually have very well coached teams.
The only other club that I would consider to be within driving range would be Pleasanton Rage, which also plays in ECNL. They haven't been too successful recently, but they seem to be improving, so that is another option.
If you're willing to commute more than an hour, there are other options, but those are your best bets close by. I would recommend looking at Mustang first.