Builders photo of SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the American Locomotive Company (ALCO) plant at Schenectady, New York in October 1937. Photo by American Locomotive Company.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the Northern Pacific roundhouse at Parkwater in Spokane, Washington in August 1955.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the Great Northern servicing facilities at Hillyard in Spokane, Washington on July 27, 1947. Photo by W.C. Whittaker.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the Great Northern servicing facilities at Hillyard in Spokane, Washington in September 1955. Photo by Stan Styles.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the Northern Pacific roundhouse at Parkwater in Spokane, Washington.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, charges out of the Great Northern Hillyard yard in Spokane, Washington.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the Northern Pacific roundhouse at Parkwater in Spokane, Washington.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at the shops at Vancouver, Washington in 1938.

SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, on the turntable at Vancouver, Washington.

Color photo of SP&S 4-6-6-4 steam locomotive Number 900, Class Z-6, at Vancouver, Washington.