Railroad Archives Online
- CollectionD0063 - Walter W. Ainsworth Collection
- Series007 - Spokane, Portland, and Seattle Railway
- Subseries Level 1014 - Photographs
- Subseries Level 2003 - Railroads--Buildings and Structures
- Subseries Level 3007 - Tunnels
- ItemWWASPSL2-014 - Spokane, Portland, and Seattle (SP&S) Cape Horn Tunnel, Cape Horn, Washington, November 14, 1907
- ItemWWASPSL2-016 - Spokane, Portland, and Seattle (SP&S) Cape Horn Tunnel, Cape Horn, Washington, undated
- ItemWWASPSL2-017 - Spokane, Portland, and Seattle (SP&S) Cape Horn Tunnel, Cape Horn, Washington, undated
- ItemWWASPSL2-018 - Spokane, Portland, and Seattle (SP&S) Cape Horn Tunnel, Cape Horn, Washington, February 14, 1910
- ItemWWASPSL2-019 - Spokane, Portland, and Seattle (SP&S) Cape Horn Tunnel, Cape Horn, Washington, undated
- 19 more...