RN's in SF are paid more than average. One google result said $95k average. I remember reading that Obstetrics nurses in SF average around $200k, they would be on the high end of RN training.
RN is definitely not a 'low paid' profession. Maybe it was years ago.
LPN is fairly low paid, I think they get about half what RN's get. LPN is also only a 1 year training program, while RN is 2-4 (and probably salaries vary based on that training length as well).
actually LPN's get around $40k it seems, which doesn't seem low for a 1 year post high school education job. More like just a median paycheck.