By any metric (overall pass rate, first time pass rate, in-state, out of state, etc), California consistently ranks at or near the bottom in terms of pass rates. The pass rates don't exist in a vacuum, and have to be compared to other states' pass rates.
The overall pass rate (55%) is low in comparison to
other states' overall pass rates, which are often in the 75-85% range. The first time pass rate is also quite low, compared to
other states' first time pass rates. A few other jurisdictions such as D.C. and Louisiana also have similarly low rates.
You said that:
"Fully accredited ABA schools from out of state often have pass rates in CA that are 20-30%"
That's actually not true. For the July 2013 California Bar Exam, the bar passage rate for ABA schools from out of state was 64.2% (906 out of 1,411 out of state students passed). That same stat for July 2012 was 63.6% (907 out of 1,425). In other words, the majority of out of state students at ABA schools pass the California bar exam.
Once again, I would argue that 63-64% is comparatively low. But here's something to consider: that statistic is an average. California attracts large numbers of out of state applicants, many from elite or at least well respected schools. Some of these schools have very high pass rates, and others look like this:
Michigan State 36%
Univ of Arizona 21%
Univ of Nevada 29%
(These are from the July, 2013 bar)
Each of these schools has an 75-90% pass rate in their home state. The 64% rate you mentioned averages these performances with those of Harvard and Yale. If anything, the out of state pass rate is probably somewhat inflated by the number of elite law grads who flock to California. I mean, how many Harvard/Columbia/Chicago, etc. grads are taking the Louisiana bar?
This article is by a prof at Pepperdine. It's interesting. He took numerous factors into account, not just pass rates, to rank the difficulty level of bar exams. Guess which ranks as most difficult? http://abovethelaw.com/2013/04/which-state-has-the-most-difficult-bar-exam/