Southern Pacific (SP) was the southernmost of the transcontinental railroads spanning Texas, New Mexico, Arizona, and California.
Included here is the St. Louis Southwestern (SSW) railway, commonly called the "Cotton Belt", who's history goes back to the 1890's. The SSW operated primarily in Texas, Arkansas, and Missouri. The Cotton Belt was wholly owned by SP since 1932 and fully merged with SP in 1992.
The SP merged with the UP in 1996 in what turned out to be one of the biggest customer service disasters in rail merger history!

SSW 9661 at Winona, MN, 11/01/02.

  SP 208 at Salina, KS, 5/02/06.

SP 7633 at Phoenix, AZ, 5/14/02.

  SP 9333 [now CEFX and on the KYLE] at Redford, KS, 4/16/06.  One of the famed "Tunnel Motors"; note the low radiator air intakes at the end of the long hood, designed for faster cooling after exiting long tunnels.

SP 7105 at Phoenix, AZ, 5/18/01.