What was the greatest challenge to completing a rail line to the West Coast?

The Central Pacific and Union Pacific Railroad's experience many unspeakable challenges along the ... The Chinese immigrant population had grown on the west coast due to the discovery of gold. ... In the end, 11 tunnels were completed. An entire camp was taken out by an avalanche, including all of its workers. Another challenge they faced was the need to create tunnels through the mountains. Using nitroglycerin, they had to blast through the mountains in a very dangerous manner.

Explanation:

Battle of Jumonville Glen, (28 May 1754), opening battle of the French and Indian War and first combat action for George Washington. Imperial ambitions and competition for the rich fur trade with American Indian tribes brought England and France into conflict in the Ohio River Valley.