Red-bellied Woodpecker (Melanerpes carolinus) at a suet feeder in Massachusetts on 25 February 2013.
This is a male, with red coloration extending over the top of the head to the base of the bill. Females would only have red on the nape (the back of the head). It's true that the "red belly" is very difficult to see and is not at all visible in these photographs.
Although its core distribution is in the southeastern U.S., this species has been extending its range northward and westward. I don't think there are any records for California yet, but correct me if I'm wrong, as I don't have any references with me right now.
Here's another image showing how well the black-and-white striped patterning on the back blends in with the bark of a pine tree.