I'm not from CA., but when mentioned I know that Police officers at one time carried Blackjacks. These were of a couple different lengths and were probably 8" to 10" in length and 2" to 4" wide, I'm sure that there were other sizes but I'm not sure what they were. These were tear drop shaped and usually filled with lead at the bottom. They had no lead at the top or handle portion as this was the flexible half.
They were used to slap various parts of an offenders anatomy, similar to the way a baton is used, to stop an undesireable action or aggression. These were used as non-lethal intermediary self defense weapons. Parts of the body that these were used on were the legs and arms, non-vital organs.
As with many things they were easy to conceal and the general public were able to get hold of and abuse their use and this is one reason they were outlawed. I'm sure there are more and better reasons why but I only know a little about these items.