What act start the railroad bloom, and how did it do so?

Pacific Railroad act enabled the congress to authorize government grants and subsidies and also gave lands to build the Transcontinental Railroad.  

From the east at Nebraska, the Union Pacific Railway initiated the construction in order to unite with the Central Pacific Railroad which was to begin the construction at the same time from west Sacramento, California.  

The two lines primarily connected at central Point in Utah which ultimately provided a clear and fastest rail route from Mississippi to Pacific Ocean. The two construction companies merged into Union Pacific railroad.

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