Subject: Driving to Green Creek Trailhead west of Bridgeport, CA
Can I take my Prius on this road, or is it too rough?

Its a washboarded but reasonably graded unpaved forest road.

I had no problem getting my Acura Integra back there- and I've seen folks get Prius's into worse places.
IMHO, take it slow and you should be fine.

Your bigger issue near term is going to be the smoke from the Rim fire.

The road is fine, no smoke today or Saturday, but it was bad Thursday and Friday.