In the early 1860s, the United States Congress approved a project to construct the first coast-to-coast railroad. Part of the Pacific Railroad Act of 1862 specified a maximum grade, or slope, of 2% for the rail line. Prior to the laying of any metal rail, the rail bed itself had to be cut through hills and lifted with fill material when necessary in order to maintain a gentle slope. The work of grading could go on independently of the laying of the rail and Congress permitted crews of the two competing rail companies to construct grades as much as 300 miles in advance of the current ends of the track. When the two companies passed each other by as much as 200 miles without meeting, Congress stepped in and dictated where the meeting of the two lines would occur: Promontory, Utah.

Here, at "The Last Cut", crews of the Union Pacific coming from the east made their last grade through the local rock. At other points along the line, the debris would have been used as fill. Here, close to completion of the line, the workers piled the debris in stable mounds, sorting the larger rocks for the bottom and smaller rocks for the top. The mounds are in surprisingly good shape today, 142 years later.