The dimensions of the canal vary quite a bit. Below Lock 5, the width is 80 feet wide and 6 feet deep Above Lock 5 to Harper's Ferry it is 60 feet wide and 6 feet deep, and above Harper's Ferry, 50 feet wide. To build the canal, the C&O Canal Company used a total of 74 lift locks that raised the canal from sea level at Georgetown to at Cumberland. Locks 8–27 and their accompanying lock houses were made from Seneca red sandstone, quarried from the Seneca Quarry, as was Aqueduct No. 1, better known as Seneca Aqueduct. This unique structure is the only aqueduct made from Seneca red sandstone and is doubly unique for being the only aqueduct on the C&O that is also a lock (Lock 24, Riley's Lock). Seven guard locks, often called inlet locks (numbered 1 through 8) were built to allow water and sometimes boats (particularly at Big Slackwater and Little Slackwater) to enter. Dam #7 and Guard Lock #7 were proposed (near mile 164 at the South Branch of the Potomac) but never built. In 1856, there was a steam pump put at that site. Later, in 1872, a new steam pump was put near mile 174. Three additional river locks were built, to allow boats to enter the canal at the river, as demanded by the Virginia legislature for buying canal stock. They were at Goose Creek (below Edwards Ferry, Lock 25), near the Shenendoah River just below Lock 33, and at Shepherdstown. The Goose Creek locks were to allow boats from the Goose Creek and Little River Navigation Company to enter. Only one Goose Creek boat was documented to enter the C&O canal, and there is no documentation of a C&O boat entering Goose Creek. The lock was eventually converted into a waste weir. The Shenandoah river (about 422 feet below Lock 33) lock let boats cross to Harpers Ferry with the mules walking on the railroad bridge, up the Shenandoah river, to the old Potomac Canal Bypass on the Shenandoah river by Virginius island. The railroad refused to let mules walk on the bridge, and from lack of business, the lock was abandoned. Stones from that lock were used for other purposes. After the 1889 flood destroyed the nearby dam in Shepherdstown, the raison d'être for the Shepherdstown lock was gone, and so it was filled in.