I heard Carl Reiner talking about it yesterday; evidently the son was leaning on a car, taking pictures of the ocean and the car slid into the canyon. Or something close to that; I had always heard he was taking pictures while driving on the Pacific Coast Highway and ran off the edge because he was taking pictures while he was driving.
Ed McM. was also talking about it last night, maybe it was the LKL show.
Yes, the son had parked on a cliff overlooking the ocean, so he could take some photos.
Ed's son also died in his 30s, he was saying, from cancer, and the very first person to call him was Johnny.
I remember when Johnny's son died in '91 -- at the end of the Tonight show after that, they showed a photo of the setting sun over the Pacific, probably one of his photos.
It was said that Johnny never got over his son's death (who would?), and that had something to do with his retiring, the next year. It must have been very difficult to go on after that, making jokes every night.