Actually I take that back, having looked a little closer at what Google really threw up. There seem to be only three separate organisations that are referenced when Googling for "atheist church", out of 3,250,000 hits for atheist + church, i.e. The First Church of Atheism, The Church of Atheism, and The First Atheist Church of True Science, none of which appears to have any solidity beyond an old website and a plea for other people to join them, which hasn't happened, because it's a stupid idea.
Then there are all the other 3,249,997 hits containing the words "atheist" and "church", which consist of the religious complaining about atheists. And commentators and journalists remarking on how absurd atheists are, having churches and all. Which they don't. Even in California.