Looking north towards the Milwaukee Road Bridge and Oregon, Railway Navigation Company's (OR & N) roundhouse. Roundhouses were used to turn and redirect train engines on to another track. Not every depot had such equipment. Usually roundhouses were only at sectional or divisional headquarters, such as Tekoa for the OR & N, or Malden for the CM & SP.

Image courtesy of Whitman County Rural Heritage.
http://www.washingtonruralheritage.org/cdm/singleitem/collection/whitman/id/525/rec/9