I think I'm one of the users JCG referred to with a son at a California D2. I would agree, generally, with everything stated here. Because I also follow many of my previous HS players and they are at various levels, I feel quite familiar with the overall environment, at least here on the west coast.
The big factors that influence D2 here (some already stated).....
start with a very large pool of players in California
Conferences - the big D2 conference is comprised of state shools and one UC, no privates - varied but generally not considered high academics, with UCSD and Cal Poly Pomona being on the higher end academically. So, acceptance is generally not a huge challenge.
California JC system - This is a biggy not mentioned yet - the JC system in California is huge, very affordable, very competitive and makes for a great pipeline into the California D2's and other schools of all levels across the country (although less so with D3's which tend to be more high academic privates who bring students on as freshmen). So, the California D2's find the JC pipeline to be a great resource for plug-and-play battle tested players. Most rosters are loaded with California JC transfers. This makes it tougher as an incoming freshman considering chances of ever earning PT. If you stand out beyond the best players coming out of the JC system, you probably would be getting D1 interest to begin with.
D1 drop-downs - Many California players do go the D1 route, in-state or elsewhere, then come home as a D1 drop-down when things don't work out as planned.
The California State school tuition structure, combined with limited athletic $, discourages out-of-state candidates.
On the other hand, there are plenty of players from colder climates that would die to play in California and have parents willing to foot the bill.
So, as a result of the large pool of HS and JC players along with willing D1 drops, the CCAA is quite competitive top to bottom. Any series can go any way. Watching across all levels, PG's assessment, of course, is a good one. Pretty simple. Top D1 better than Top D2 better than Top D3, etc. Best of the lower level can beat worst of the higher level.
NAIA - Most in this region are small private Christian schools and there are not all that many. There are a few good teams (Westmont) but several teams are really not good. The poor conference competition hurts the better teams come post-season. The best NAIA's did compete with bottom D2's but the few meetings were mid-week non-conference so not sure those head-to-heads held much merit. Just evaluating talent, the good NAIA school wasn't quite there and definitely had less quality depth.
D3 - In this region is similar to what I described with NAIA but less bad teams. Mostly small private Christian schools. The better teams (Cal Lutheran) would benefit from better competition.
The D2 in this region is certainly better top-to-bottom than D3 or NAIA but, again, the top lower level teams can compete with the middle D2's.
Having seen both Westmont (NAIA) and Cal Lu (D3), there is not significant difference between the two. Having watched Cal Poly and other D1's, the D2's here don't have the depth of pitching or position bench depth and you'll get a few players starting at D2 who don't quite have D1 bodies
PS - proud to say our little HS currently has players contributing at schools across all of these levels of play, including the very good programs mentioned.