I don't think there ever was a "lot" of intermodal in the 80's. I can't think of any solid intermodal trains being operated, just the odd car or two in the regular trains. It was cheaper to send your intermodal traffic to LA and have it go over the road to San Diego than go by rail.

A question I have is what year did the "Night Coast" go away? Must have been around 1980 or sooner. After that all you had were the Barstow trains and they would have had to capture intermodal traffic off through trains at Barstow. If you wanted to count the auto trains as intermodal that would change my answer a little. They also used to export potash in solid unit trains, do they still do that?