Sounds like chiggers to me; I sure wouldn't rule them out. I know that chiggers are supposed to be a problem of the eastern U.S. but I also know that we have them locally here in S.E. Arizona. This is apparently true for some locales in California as well http://www.chacha.com/question/do-you-have-chiggers-in-california

I have picked up the typical ring of itchy little bites around the top of my socks in several parts of Arizona but never in California even though I'm a native son. I suspect that whether you get chigger-ed depends on where you go. I find that grassy, oak-savannah vegetation is great for Arizona chiggers.

I don't think they would last out a good washing in socks but it probably wouldn't hurt to dust the socks with some pyrethrum insecticide and then wash them.

For me, the only relief I can get from the itching of the bites, which seem to last at least a week, is to scratch with a good stout wire brush The itch always seems to come back though