T.C.
I find it's actually really easy to meet other moms in this area. Just go to the park or Barnes and Nobles or the local library toddler story time, you'll meet other moms with toddlers and newborns really easily. No need to pay to join any groups!
I live in Dublin and have a 7 week old and a 2.5 year old daughter. I'm on maternity leave so am open to playdates and get togethers, but Dublin might be kind of far for you. I'm sure you'll find many other moms in Walnut Creek.
Good luck. It's good for you to get out of the house and socialize, hopefully every day!