It was Lincoln who wanted the transcontinental railroad built and pushed for it. The railroad used to go along that path...but then later moved. This section is the highest elevated section of the railroad.
Why not do a web search and find out.
The route used by the railroad was abandoned and rerouted further south. In 1930 it was used to create a section of one of the first transcontinental highways and the monument was created as reminder of the Lincoln's foresight.
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