The Monterey Pass Battlefield is a Historical Park in Washington Township, Franklin County that commemorates Pennsylvania's second largest Civil War battle. The Battle of Monterey Pass was fought for over ten hours on a rugged mountain, in a blinding thunderstorm during the middle of the night on July 4th & 5th, 1863. The battle spilled over into Maryland during the early morning hours of July 5th making it the only battle to be fought on both sides of the Mason Dixon Line. In the hours after the battle, more than 80% of the Confederate army marched through Monterey Pass, and many thousands of soldiers bivouacked there.