Ellensburg CM&PS Railroad Bridge Across Yakima River
Chicago, Milwaukee & Puget Sound Railroad Bridge (Formerly CM&SP)
c1910 RPPC Postcard Image by David Shedlock in October 2017
BH Photo #407644
David, I believe the bridge in the postcard you posted is of this bridge: https://bridgehunter.com/wa/kittitas/milw-lake-easton/
Reasoning being that that's a spot where the Milwaukee Road crosses both the Yakima and Northern Pacific, something that doesn't happen near Ellensburg, based on old maps.