What were the names of the companies that built the Transcontinental Railroad?

Train tracks linked thousands of towns and cities in the eastern United States by the mid 1800s.  There was a lack of railroad tracks in the western part of the country.  All that changed in 1862, when Abraham Lincoln signed the Pacific Railroad Act.  This bill stated that two railroad companies would build tracks to connect the East and the West.  One company would start in the Midwest and build their tracks west.  The other would start in California and build their tracks heading east.  The two railroad companies would receive money and land for each mile of railroad track laid.

The two railroad companies were the Central Pacific Railroad Company and the Union Pacific Railroad.  The Central Pacific Railroad Company started in the west and headed east.  The Union Pacific Railroad started further to the east and headed west.  They met in the middle in Utah in 1869.