How did leland stanford make his money?

Leland Stanford was an industrialist, business tycoon, politician, and the founder of Stanford University. During the California Gold Rush Stanford moved to California and started a whole sale business which grew as the economy boomed.  Stanford helped to found a major railroad company the Central Pacific Railroad and went on to make large amounts of money, enough so for many to consider him a "Robber Baron" a name given to wealth and powerful 19th century American businessmen.