Back in the good old days, people used plywood and plaster to build their layouts. The idea of using foam for scenery and layout bases has exploded in the last ten years. You can still make a layout with plywood and plaster if foam is not available. The white bead foam will also work for scenery, but isn't strong enough to use as a layout base under the track. The only drawback to the white foam is it is considerably messier to work with.
As to where to find pink or blue foam in california - beats me. I have heard there are dealers but you may have to drive for awhile. Pink or blue foam is not very common in southern arizona, either. I can find blue foam in home depot in 1" sheets only, and even then is it often out of stock.
Kevin