Interesting question about valuation maps for the South Pacific Coast Railroad. Valuation Maps document the value of railroad trackage, rolling stock, and other assets to determine each railway company's value. The South Pacific Coast Railroad was leased (then purchased) by the Southern Pacific Railroad and ran a line between Alameda and Santa Cruz from 1876-1940.
We own copies of various maps authored by the "Southern Pacific Company" and published by the Valuation Department (SF, CA) in 1877 (Search CRUZCAT under author name):
G4364.S69P3 1877 .S6
G4364.S69P3 1877 .S62
G4364.S69P3 1877 .S63
Rick Hamman's book "California Central Coast Railways" is a good resource (HE2771.C2 H35 2002)
See "Railroads" in the cartobibliography binder for more info.