Lock 9 of the Union Canal Company's Branch Canal to Pine Grove was part of a canal system that operated from 1830 until 1862, carrying coal from the mines north of Pine Grove to cities including Baltimore, Philadelphia, and New York. The original lock at this location was a much smaller wooden structure, but in 1851 it was rebuilt in stone and enlarged to handle boats carrying up to 80 tons of cargo. Here, four canal locks used the power of water to raise boats traveling upstream for Pine Grove about 34 feet to the reservoir water level behind the Big Dam and then lower them on the return trip.