So California doesn't have any sort of no-tolerance drug and alcohol policy at work or anything?

Not as far as i know. I mean, i imagine most companies do, but i don't believe it's a state law or policy.

I don't know if this got started during the dot bomb as a cultural thing, but that's certainly where i first encountered it. It definitely is a problem for the reasons you listed. I'd like to think that we policed each other well, and i never heard of anyone getting plastered until after they left the building.