Feather River high line

I am from Australia and I spent two days along the feather river route. The first day a empty stack train came off the high line heading towards Oroville. The next day a empty stack train was heading north along the high line. Can anyone explain this for me. Thank you

Refered to as "Bare tables",they both were equipment moves to "where they are needed" from "overstocked" yards after unloading
the containers from the cars

Where does the high line heading north end up. Thank you

It dead ends into the Columbia River Gorge, where trains can head either west to Vancouver/Portland (and then north to Seattle, likely the destination of the train) or east to Pasco.

Has the Union Pacific ever used the high line?

UP has rights from OT Jct(UP's Portland Sub) to Biebier Line Jct(near Klamath Falls) on the BNSF's Oregon Trunk Sub.
At Chemult,it becomes UP's Cascade Sub.