That's a really unappreciated part of RR history. The amount of manual labor that went into to building so much of the country's RR infrastructure. Picks, Shovels and maybe horse drawn Fresno scrapers. Its also a testimony to the engineers and surveyors who laid out those routes trying to take advantage of the terrain where they could to minimize earthwork.Not always the shortest route vs. least earth to be moved.
Steven Ambrose touches on this in "Nothing Like it in the World" about the building of the Transcontinental RR.