In April 1866, three crates of nitroglycerin were shipped to California for the Central Pacific Railroad, which planned to experiment with it as a blasting explosive to expedite the construction of the Summit Tunnel through the Sierra Nevada Mountains. One of the crates exploded, destroying a Wells Fargo company office in San Francisco and killing 15 people. This led to a complete ban on the transportation of liquid nitroglycerin in California. The on-site manufacture of nitroglycerin was thus required for the remaining hard-rock drilling and blasting required for the completion of the First Transcontinental Railroad in North America.