I've been waiting for Severe Duty or someone else in the know to enlighten us about this train. I can only guess. But here is a guess:

I don't think there are currently any on-line customers on the Stampede Sub, all the way from Auburn to Ellensburg, except the chip plant at Bull Frog just west of Cle Elum, which operates sporadically and is served by through trains when it does.

This local is too far east to be turning on the Stampede Wye, which trains sometimes do.

So that leaves this guess: that spur in the road in the second picture goes into a gravel pit that sometimes has hoppers on the end of the spur. There is a redimix plant back in there, so I have guessed that the hoppers bring in cement for that plant. The next to the last car in this train looks like one of the hoppers that are spotted in there.

Did you leave right away? Did you see where the train went? Could it have backed into that spur?

Work trains go east on the sub sometimes, but not locals. I'm guessing this train served that spur.