If you want to model Cajon Pass, it is big enough that you could make a huge model railroad that is entirely taken up with Cajon Pass. In that case you would not have room for industries, just rains going from staging through the pass and back to staging. I would guess from what I see here in So Cal that 90% of BNSF's traffic is now intermodel. There are also a bunch of autoracks loaded with cars coming out of the L. A./Long Beach Harbors, as well as West bound autoracks coming out of plants in the Eastern US & Canada. We ship more citrus than ever out of So Cal, but most of the citrus crop is shipped by truck rather than train, although there are a few refrigerator cars going out.
Another industry to consider in So Cal is cement. I don't know how it compares to other parts of the country, but gypsum mining is huge in Riverside & San Bernardino Counties. There are litterally whole mountains of the stuff that are being cut down, and hauled off to make cement. Of course along with the gypsum, there are also sand & gravel quarries to provide the other ingrediants for cement. There are also ready mix plants receiving gypsum, sand, and gravel to make cement for construction projects from home building to roads, to high rise office buildings and tilt up ware housing.
In Los Angeles there are a lot of grain elevators. We don't grow much grain out here, but with millions of people in the area, we have a lot of big bakeries to turn the grain into bread, as well as a few major breweries that use malt, hops, and grain to make beer. We also have milling companies with grain elevators that make flower, or process sugar to supply all of the donut shops, local bakeries, etc all over the area.
Finally there are mega-warehouses all over the area, the biggest ones tending to be in Fontana & Ontario areas that receive or ship just about any roduct you could think of such as food, electronics, appliances, or plumbing supplies. In fact if you look around your house, virtually everything you see that was manufactured, was stored in a warehouse somewhere at some time. This is probably equally true of any large metropolitan area in the country.