River Road (MD 112), , Poolesville, , Montgomery County
The Seneca Stone Quarries are located on the Chesapeake and Ohio Canal and the east bank of the Potomac River near the village of Seneca. The north retaining wall of the canal, a culvert to conduct a small creek under the canal at the west end of the quarry, and the Seneca Aqueduct, which carries the canal over Seneca Creek, are constructed of the local Seneca stone. Only two buildings stand in the quarry area: the cutting building at the east side of the quarry, and a duplex on the hill overlooking the quarry and river. Both structures are in ruins and constructed of Seneca stone. The cutting building for "working" architectural blocks was built probably in the 1830s, and later doubled in size to its present dimensions. Only the stone walls remain. From the south gable end facing the canal, the outline of a low-pitched roof can be traced. The stone is rough finished in rectangular blocks. Probably dating from the mid 19th century, the duplex on the hill is built of rough rubble stone laid in regular courses except at the corners, sills, and lintels. On the east facade, the latter are smooth-finished rectangular blocks. Some of the same smooth blocks were used as paving, leading to the two east doors. The 2 1/2-story structure had two rooms on each floor of each unit. A single fireplace was located in each west room. Most of the south gable has collapsed beneath the roof. One dormer on each side of the roof lights the attic chambers. The major part of the quarry is located south and southwest of the duplex. Its red walls and rough floor are overgrown with an accumulation of vegetation and look as though they had never been disturbed.
The Seneca Quarry was the source of stone for two Potomac River canals, the Potomac Company and the Chesapeake and Ohio Canal Company (1780s to 1820s), and for the Smithsonian Institution (1847-1848). After its construction, the C&O Canal was often used to transport the stone from the quarry. Water from the canal was also diverted to provide power for the machinery used to finish the rough blocks. By 1900, quarrying operations at the Seneca Quarry had stopped. The quality of the remaining stone had deteriorated beyond the point of usefulness.