Why are some of the counties in California so big and others are like 1/10the the size of the big ones?

Question

San Bernadino county is huge!

Answer 1

You will notice a lot of little counties in the area east of San Francisco up into the Sierra.  Those counties were formed in the early days of California when that is where most of the population resided due to the gold rush.  The counties were small because the goal was to allow a person to get to the County Seat within a day (and they were walking or on horseback).  The counties to the north and south had less population, and small divisions simply did not make sense.

As the population grew, so did the speed of transportation, so larger, more populous counties became feasible, but, of course, no smaller county wanted to give up its independence to be joined with another.  The larger counties were broken up somewhat as they became more populous.  Orange County split off from Los Angeles, Imperial from San Diego, etc.  As the "Inland Empire" grows, there may be pressure to divide San Bernardino into more than one county, but the size of the sparsely inhabited desert areas is always going to result in county of substantial size.

Answer 2

historical reasons

Answer 3

mostly because if you look at the map it is almost all land, and very little population center;

most counties are centered around population hubs; for instance SanFrancisco City and County are the same thing; there is no room outside of the City of San Francisco;

Los Angeles County is mostly population; however, at one time about 60 years ago it was actually very rural!

OC; mostly population but some green areas remain; SanDiego is a huge county; and at one time the population was centered closer to the ocean; now it is spread out all over the county.

so Kern, San Berdo, and San Joaquin, a lot of land and not so much population hubs.  

that is about it.