- "Shit, it's the Cavalry!"
The U.S. Cavalry was the mounted reconnaissance, surveillance, and target acquisition branch of the United States Army. They rode their horses, to monitor the territory surrounding Hill Valley, in 1885.
On September 2, the cavalry began a chase of Pohatchee Indians, which ran into the DeLorean time machine. They chased the Pohatchee past the bear cave and continued after them as Marty McFly watched from the safety of the cave.