This is UP 1983, one of the railroad's "heritage" units, all of which are numbered for the year the subject road became part of the Union Pacific. UP 1983 is the Western Pacific heritage unit. Like all of the "heritage" locomotives, it wears a paint scheme inspired by the predecessor road, but not an actual scheme that road ever used. But it does have a prominent WP "Feather River Route" logo on its side.
Amtrak came through almost exactly on time, and just a couple of minutes after it passed, the intermodal train started back up and continued west.