I have a rare copy of a classic book - A Century of Southern Pacific Steam Locomotives - that contains a complete set of eighteen plates showing the various Divisions of the Southern Pacific Rail Road. All the way from Portland to New Orleans via southern California! They represent the SP at its zenith (c. 1920 tho' each map may have a slightly different date on it).
The maps were only published with the book and many of the copies have, I am sure, been lost for ever. So I have scanned them (they are too large for a single scan per map so will have an imperceptable "stitch" down the middle) and made them available on focalplane.com for download as quality jpegs.