This aqueduct on the Sideling Hill Creek is a 70 foot single arch of limestone. The creek marks the boundary between Washington and Allegany Counties.
Near Lock 51 about a mile from Hancock is the Bowles House, now Hancock's C&O Canal Visitors Center.
At mile 122.96, above Lock 52, is the Tonoloway Creek Aqueduct, locally called the Bowles Aqueduct. This aqueduct is notable for the use made of the natural rock outcroppings on both sides of the creek. On the upstream side these serve for the aqueduct's abutment, resulting in an irregular arch. On the lower berm, where there is a waste weir, the spillway is on the natural rock.
This aqueduct carries the canal over the Tonoloway Creek, near Hancock. It was built between 1835 and 1839 of limestone quarried up stream on the creek. Some of the cement for the construction came from Boteler's Mill near Shepherdstown.
The Licking Creek aqueduct, built between 1836 and 1838, is a 90 foot single arch structure of limestone.
The Canal Company claimed in 1839 that this was "one of the longest, if not the longest aqueduct which has been constructed in the United States".
In 1920 the berm side of the Conococheague Aqueduct failed. The level between dam 5 and lock 44 was drained of water as the entire wall collapsed into the Conococheague Creek in Williamsport. At the time of the wall failure a boat was in the process of crossing and it was swept over the side of the aqueduct and ended up in the creek. Towns people from Williamsport crowded onto the canal to survey the damage.
In 1920 the berm side of the Conococheague Aqueduct collapsed into the Conococheague Creek. The current created by the canal water flowing over the edge of the aqueduct caused a canal boat to plunge into the creek below. The canal boat stayed in the Conococheague creek until the 1936 flood carried it under the aqueduct and down the Potomac Valley.
The original text written under the photograph stuck into an album read "Coming through the Viaduct."
Photographs such as this one that show the Conococheague Aqueduct with a stone upstream wall were made prior to the wall’s collapse in April, 1920. The stone wall was subsequently replaced with a wooden wall.
The Conococheague Aqueduct was completed in late 1835. This picture of the aqueduct was taken after the aqueduct wall had collapsed and been rebuilt in 1920 and before the 1936 flood when the wood repairs were washed away. The photograph is looking up the Conococheague Creek toward Williamsport. Before the construction had finished in 1835, Eli Beatty had already applied for the use of the water from the flume that would be constructed on the upstream side of the aqueduct. The use of water power at Williamsport would power multiple milling operations.
This was Aqueduct No. 4 of the series of eleven aqueducts over major tributaries and like No. 3 over Catoctin Creek, it was built with an elliptical central arch. In July 1864, as part of General Jubal Early’s attack on Washington, there were Confederate actions in the vicinity of the aqueduct that included the burning of canal boats, and an effort to destroy the aqueduct itself.