Plum Run rises on the Codori farm and drains the area between Cemetery Ridge and Seminary Ridge south of Gettysburg, flowing south past the Trostle and J. Weikert farms, through the Valley of Death between Little Round Top and Devils Den, past the Slyder farmhouse and finally leaving the battlefield between Big Round Top and Warfield Ridge. It eventually becomes part of the Monocacy River and the Potomac.

Its location at the heart of the heaviest fighting on July 2nd and 3rd makes it one of the most fought-across streams in America, but nowhere on the battlefield does it serve as even a modest barrier to movement.