Does anyone have any information on California law regarding side marker lights? Are they required?

Not if they weren't origionally equipped on the car. If they were then yes they are required.

That said, if you were to remove all evidence of side marker lights from your car I very much doubt that you'd fail any car inspection that a roadside cop might give you. They are smart but not that smart.

SMOG checks do not count. Thats not what the techs are trained for.

1968 and later require them.

1968 and later require them.

Yep, seems like any car 1967 and prior didn't have them....1968 and onwards did....the cops probably know this too...