Welcome to our little corner of the universe. The Santa Cruz Atheists meetup group is now defunct, and I don't know of any other local activist groups. For socializing, though, two meetup groups have sprung up recently. Lemme know if you want more info. How long have you lived in Santa Cruz?
Welcome to Atheist Nexus with its 9000+ good friends and discussion groups.
Among the groups, may I suggest trying the busy group “ORIGINS: Universe, Life, Humans, Evolution, Religion.....” with its 130 commonsense topics whose discussions rebuff religious nonsense. You will be welcome.
One discussion is "Proud to be Atheist" (74 posts) seeing that atheists and humanists hold the intellectual high ground compared with the pathetic superstitions of the god followers.
Terry Meaden (English archaeologist; founder of “Origins”)