My wife and I found this road 10 years ago when she was my girl. It took us another 10 to find it again. Found it the same way we did the first time; by day-tripping and getting lost with nowhere to go but forward.
This time, the fires of a couple years ago have done away with the abandoned, 60's hot-spring spa. But the twistys, slow curves, wide open space and cows are a welcome relief from the bustle of Orange County. If you're looking for knee-dragging fun, I haven't found a time of day for it yet. Seems like too much of a thoroughfair after 5pm during the week and weekends about the same. Mainly a cruise route in the open air with plenty of places to stop, spread out and just breath.
Head out towards Yorba Linda anyway you can, hit Lambert and head East. Lambert becomes Carbon Canyon Road. 30-40 minutes of taking it easy, taking in the scenery dumps you out in Chino.
Turn around and enjoy it in reverse or hang a right on Chino Hills Pkwy to the 71East/South towards the 91 and you're headed back to the nuts of Orange County.
Enjoy and GET LOST!