"THAT AFFAIR AT LEESBURG": MILITARY GEOGRAPHY AND GEOLOGY OF THE UNION DEBACLE AT THE BATTLE OF BALL'S BLUFF, LOUDOUN COUNTY, VIRGINIA, 21 OCTOBER 1861

The Civil War battle of Ball’s Bluff, fought on 21 October 1861, resulted from the ill-fated attempt of 1600 Union Soldiers to cross the Potomac River at Balls Bluff, VA, in order to probe the lines of an equal number of Confederates assembled around Leesburg. Not only was the endeavor poorly planned and led, but also the topography of the invasion site on the Virginia side of the Potomac, opposite Harrison’s Island, MD, formed a natural death trap.

Ball’s Bluff is situated in the northern part of the Mesozoic Culpeper Basin, the cliff exposing thickly interbedded Triassic-age Leesburg limestone conglomerate and grayish-red, calcareous Balls Bluff siltstone, both locally karstic. The bluff extends 2 mi along the west bank of the Potomac. At the battlefield site near its north end, it reaches its maximum height of 100 ft between two deep ravines 1700 ft apart. The upper half of the bluff is a rock cliff, and the lower half a steep talus slope. Between the bluff and the river is a narrow floodplain. The river between the Virginia shore and Harrison’s Island is 250 ft wide. At the top of the bluff between the ravines in 1861 were a stand of woods to the north and an open field to the south. This landscape profoundly affected the course and outcome of the 10-hour battle that raged here.

Misled by a faulty night reconnaissance, a small Union force from Gen. Charles Stone’s “Corps of Observation” crossed the Potomac early on the morning of the 21^st and advanced westward, expecting to surprise a non-existent Confederate camp. When Confederate resistance materialized, the Union position gradually deteriorated. Union reinforcements were sent, but the Potomac was running high; too few boats were available; Gen. Stone failed to monitor the situation, leaving tactical decisions to the brave but incompetent Col. Edward Baker; and Col. Nathan Evans handled his rebel forces masterfully. By the end of the day, the Union soldiers were driven off the bluff and caught in a deadly trap on the narrow floodplain, virtually leaderless (Stone was dead). Unknown numbers drowned or were shot trying to swim to Harrison’s Island, and many others were captured. The battle of Ball’s Bluff resulted in the rather pointless deaths of hundreds of Union men. It also led to the formation in the U.S. Congress of the Joint Committee on the Conduct of the War, whose first victim was Gen. Stone.