marker that we saw covered two battles, it did not give much detail about the retreat from Gettysburg. I figured there would be markers across the river with more information and found one on HMDB telling how wagoners helped save Lee's army at Williamsport. I looked on the Maryland Civil War Trails list and found mention of a marker on the C&O Canal which is only accessible by hiking or biking 2–3 miles from Williamsport! Fortunately someone has shared a photo of this marker on TripAdvisor. I've transcribed most of the text although I'm not sure if I'm reading the numbers correctly as it's a small photo and the sign is not totally clear.
"Just Charge it to Jeff Davis"
The Potomac River trapped Gen. Robert E. Lee and his Confederate army during the retreat from Gettysburg. Flooded by torrential rains on July 4, 1863, the Potomac raged for more than a week, preventing Lee from crossing into present-day West Virginia. Complicating matters, on July 4, Union cavalry operating behind Lee's army had destroyed the pontoon bridge here, severing his umbilical card to the Confederacy. Finally, on July 10, the Confederates completed a pontoon bridge, but it took 3 days for the ambulances and hundreds of ordinance and artillery wagons to cross. By the early morning of July 13, during another downpour, Gen. James Longstreet's infantry corps began tramping across, guided by bonfires on both shores and signal torches on the bridges. Gen. A. P. Hill's corps followed, and by mid-morning the next day 30,000 Confederates were across. Lee's army had escaped.Another source tells us that Union General Buford's men arrived at the river a little too late. "As our troops neared the bridge," Buford recalled, "the enemy cut the Maryland side loose, and the bridge swung to the Virginia side."