I've been working on this issue for awhile now as residency approached for me. Here's what I've gathered from a couple of friends who've made it (as FMG's, incidentally):
In terms of strict competition for residency spots, that fluctuates just like anywhere else. The typical rules apply (academic, urban generally more competitive). Often, you can find stats on applications received vs. positions offered and do the math yourself.
The problem with CA is their licensing board requirements, which are above and beyond the requirements to get a residency. You need the dreaded "California Letter", which is granted by the CA licensing board and the residency programs have nothing to do with this. So, you can get accepted to a CA residency thru the match, the program could love you and be ready for you to start, but it will be illegal because you don't have your CA letter.
I'm a CA resident, but an FMG, so I'm describing what is needed for types like me. Maybe out of state but USMG's don't need the letter. As I understand, however, there are additional problems for everyone who is not a CAMG created by the licensing board. They do this for the simple reason that doctors per capita in CA are about as dense as it gets, and they're trying to thin things out.
Just my take on the issue. Maybe it helps. Good luck.