The reason why it's illegal to wear cowboy boots in California is due to a quirky, Blythe, California, ordinance, which stated that you can't wear cowboy boots unless you own at least 2 cows.
The old law on being illegal to wear cowboy boots in California was not a statewide law, and only was a law that it was illegal only in Blythe, California under their ordinance to wear cowboy boots.
The law on making it illegal to wear cowboy boots unless you owned at least 2 cows in Blythe, California, was meant to distinguish genuine ranchers from fashion wearers of cowboy boots.
Although it's rarely enforced and mostly a fun local oddity.
Other towns also have odd and quirky rules, such as Carmel, California requiring permits for high heels or even Stockton California having a law that once banned wiggling while dancing, which shows these laws are not about cowboy boots, generally but local flavor.
Blythe, California that put the ordinance in place that made it illegal to wear cowboy boots is a small city located near the Arizona border.
The rule stated that you must possess at least 2 cows, to legally wear cowboy boots within city limits.
The purpose of the law was to ensure only real cowboys, that were tied to agriculture, wore the cowboy boots and not just trend followers or tourists.
It's now though a largely historical curiosity and a piece of local folklore, and not a serious law that is actively policing footwear so you could wear cowboy boots in Blythe, California now without any issues.
You might get a chuckle when wearing cowboy boots in Blythe, California, but you won't be arrested or cited.