There's a couple more locations that CDoherty brought up which I forgot weren't part of the Hazzard Square thread, so you may have missed them:
Mystery Location
This one covers locations used in 'Comrade Duke' (and other episodes), most notably the airfield (now a plowed field) and a familiar stretch of tarmac called Pico Canyon Road. Both are quite near the Indian Dunes (Styx River jump etc.) that you mentioned. The airfield location is visible from Henry Mayo Drive, but Pico Canyon Road is part of the Newhall Ranch so I doubt if it's open to the public.
Mystery Location II
This one has the location of the fight at the end of 'Welcome Back Bo and Luke' and also covers the railroad jump in 'Grannie Annie'. Both are in Oxnard, which may be a bit out of your way.
Both threads have Google Maps links to the locations discussed.
Lastly, I barely mentioned Piru in the Hazzard Square thread (it was only going to be about the WB back lots when I started it ). It's only a few miles west of the Indian Dunes. The race in 'Luke's Love Story' goes through Piru, and many of the locations are virtually unchanged. Piru also appears in 'Officer Daisy Duke'. The bridge at the east end of the town featured in a couple of episodes and, although bypassed with a new bridge, is still standing (as far as I know). Head a couple of miles north on Piru Canyon Road and you'll reach Lake Piru. A couple of episodes were filmed here including 'The Great Insurance Fraud' where Coy thinks he's caused conman Ward's death when his car goes into the lake.
Looks like I may have to add a couple of posts about Piru to the Hazzard Square thread, but I doubt if I'll have time before your road trip.