Mother's Clubs in Walnut Creek, Pleasant Hill, Concord, Clayton, Martinez, Lamorinda and Danville - East Bay. Mom's Clubs are a great way to meet other moms in the area!
The Contra Costa Moms Meetup Group (central Contra Costa County)
Hilarie's Helpful Hints is a meetup group offering activities in the East Bay.
Mt. Diablo Mother's Club serving Walnut Creek, Pleasant Hill, Martinez, Concord and Clayton
MOCHA Moms (serving multicultural moms from Contra Costa County)
The Mamahood - SF Bay Area (online only Facebok group but one massive hive mind! Lots of subgroups too. Highly recommend for all East Bay moms looking for any resource, ever.)