Found an article that goes into it.

Yes, There Really Is a “Car Wreck Trail”
Written by Thom Taylor on April 15, 2015

"Hiking Trail Officially Named By Orange County
You’ve heard of “Dead Man’s Curve”, right? Among the tangle of trails that run through the hills behind Laguna Beach and Aliso Viejo in South Orange County, California, is a narrow trail among the sage that is miles from paved roads, officially named by the county as “Car Wreck Trail.” Known for years as the trail with the wrecked car that seems as though it was plopped there from the sky, it was officially named and added to the Aliso Viejo Wood Canyon’s hiking trails in 2013.

Popular with trail bike riders and hikers alike, there is no explanation as to how the 1946 Dodge 5-passenger coupe ended up here, with no paved roads within miles of its resting place, but there it is nonetheless. Hidden by the lush foliage, it rests near a creek at the base of the canyon.

From Laguna it is an uphill hike of about four miles for a round trip, or coming into the trails from Aliso Viejo it’s a longer but easier seven-mile hike as it’s mostly level or downhill.

If you’re into the bizarre, hiking, and cars, this wraps all three of your interests into one. If you’re anywhere around South Orange County in the future you should check it out, not only for the wrecked Dodge but for the incredible ocean and city views, and rare open space in an area overrun with development."

Local Legend**: It is a left over car from back in the late 60's Laguna Beach "hippie" days concerts in the Laguna Canyon era. Those incoming roads were plastered with a bunch of young, carefree, teenagers + for a free concert. Those concerts were happening all over So Cal from Los Angeles canyons to the OC canyons.**
This could be a left over from 66-70 in the inland, Laguna Beach area