The same railway lines can have different names over time. It gets confusing. Here is the list of railroads, merged, re-named, etc. from Wikipedia.
Here's what I just read here:
In 1885 the Central Pacific Railroad was leased by the Southern Pacific Company. Technically the CPRR remained a corporate entity until 1959, when it was formally merged into Southern Pacific. (It was reorganized in 1899 as the Central Pacific "Railway".) The original right-of-way is now controlled by the Union Pacific, which purchased Southern Pacific in 1996.