Hey folks, having trouble finding any information about this. Is it legal to make a u-turn at a four-way intersection with two stop signs?

I was in a minor accident tonight (in my car) where I had stopped, made a u-turn at a four-way intersection with two stop signs (quiet street in Cap Hill), and the guy that was behind me at the stop sign turned left and hit my left-rear quarter panel as I was completing my u-turn.

Only thing I've found is a California law that states that "Drivers may legally make U-turns at four- and two-way stop signs, as long as there are no signs prohibiting the move and no oncoming traffic makes it hazardous" and read somewhere that the driver in the intersection has the right of way until he/she clears the intersection. Obviously California law doesn't mean jack here, but that's all I've found.