Single stall bathrooms usually have locks on the door.
Single stall bathrooms are usually open to anyone, one at a time (to prevent people from having sex in them or being attacked in them/molested)).
Somewhere in time, National Lampoon addressed this issue with a cover that showed, from the back, three people at standup urinals. Two were men and one was a woman (by their clothes). All were standing up.
It was a pun on equal bathroom rights. If anyone can find that cover, please post it here. You’ll see what I mean.
As for California, “PEES be upon you”