I got my answer. On todays Trains newswire, it states:
• Southwest Chief — A freak snowstorm between Dodge City, Kan., and Lamar, Colo., on Sunday caused significant delays to westbound train No. 3 that left Chicago Saturday afternoon. It was running more than 15 hours behind schedule into Los Angeles on Monday after operating on restrictive signals while a BNSF Railway track inspector protected highway crossings during whiteout conditions; eastbound train No. 4 is more than 6 hours late into Chicago on Monday.
And somehow L.A. was able to provide a set of equipment for # 4 (1) even though #3 had not arrived. Sunset equipment?