What kinds of difficulties did the builders of central face?

here were many challenges to building the railroad east from Sacramento, CA. The first, and most difficult challenge for both companies building the transcontinental railroad, was the Sierra Nevada mountains.

But even before they could make it to the mountains, the company had to get most of the materials they needed from the eastern US. That meant the supplies had to come by boat. It took six months to sail from New York to San Francisco.

There were no significant issue building the road from Sacramento until they reached the slopes of the mountains. Open land gave way to dense forests with thick brush. The trees could be 150 feet high. (45.72 meters)

Winter in the mountains is never an easy season and the more snow, the harder it is to move around. The first summer the crews were in the Sierra range, there were 42 snow storms. The crews tunneled into the huge piles of snow and made camping spaces.

The tunnels were the hardest thing they did. The drilled holes and filled them with black powder. An average day made one foot of progress into the stone face. They built 15 tunnels from 92′ to 1,659′ for a total length of 6,213 feet. This was all through solid granite. They finally used nitroglycerin beginning in tunnel #6.

I don't know if this is what your looking for but I hope it helps...

answer; software failure, and human error;