Berkeley and U of Washington have a lot of history with very old chapters and several of them. Arizona has a decent amount of chapters, as does UCLA and Washington State. Pepperdine seems to have a thriving young system.
I'm not from that part of the country, but from the posts we see on these boards, the Greek scene out there faces a lot of competition from other organizations and other distractions (great weather, sports, etc). There seems to be a lot of anti-Greek sentiment in that part of the counrty as well. Of course that's a gross generalization, but still.
Check out my thread
here, that lists the NPC sororities at every school. You'll get an idea of where Greek life is big.