Some excellent info and pix re Capitol Milling may be found here:
http://lariverrailroads.com/capitol_mills.html
Pacific Coast Architecture Database (PCAD) adds this:
"Alteration Note: In 1898, Morgan and Walls added a third story to the rear wing of the Capitol Milling Company Building and and added a fifth story to the main building."
https://digital.lib.washington.edu/a...ructures/3475/