SP&S 4-6-6-4 steam locomotive, Class Z-6, with a westbound freight east of Home Valley, Washington, undated. Photo by Photo-Art Commercial Studio.

SP&S 4-6-6-4 steam locomotive, Class Z-6, with a westbound freight east of Home Valley, Washington, undated. Photo by Photo-Art Commercial Studio.

SP&S steam locomotive with a passenger train at Tunnel Number 2, 1916.

SP&S passenger train passing Castle Rock (Beacon Rock), July 7, 1914.

Color postcard view of SP&S steam locomotive with a westbound passenger train at the Cascades of the Columbia River, Steamboat 'Bailey Gatzert' on the river, postmarked September 18, 1913. This is a postcard image.

Color postcard view of SP&S steam locomotive on passenger train showing Columbia River and Cascade Mountains, postcard issued by SP&S, postmarked September 4, 1925. This is a postcard image.

SP&S steam locomotive with a westbound passenger trainat the Cascades of the Columbia River, Steamboat 'Bailey Gatzert' on the river, undated.

SP&S steam locomotive with westbound passenger train exiting tunnel along the Columbia River, undated. Photo by Angelus Commercial Studio.

SP&S steam locomotive with eastbound passenger train along Columbia River, undated. Photo by the Kiser Photo Company.

A leased Great Northern steam locomotive is seen on a a work train during construction of the SP&S, undated.