There is a nice road that connects the 5 to the 15 in south OC... I would guess just south of Lake Forest/Laguna Hills area cutting accorss to the Temecula area. I've driven this road once and and its fun to drive. There is also another similar road between Yorba Linda and Chino Hills although not as long. My favorite in my neck of the woods is at the end of Chapman/241 ... just be careful with the roadies (me included).
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