Well at least I know why I saw a BNSF caboose behind a small train (about 20 car) 2 years ago at the base of Cajon Pass.
Other caboose I have seen in the past few years was a UP one on the back of a 3 car work train pulled by a UPY engine running between Salt Lake and Ogden. The same caboose sat for two years in the Riverdale UT yard, but I think it recently moved,
I also saw some sort of private company caboose on a mainline freight about 4 years ago, it was directly behind the engines. It was bright white with green lettering, dif not catch the name on it though
