The Three Sisters are three rocky islands in the Potomac River in Washington, D.C., west of the Key Bridge. A notable landmark in colonial times, the islets are less well known as the Three Sisters Islands and Three Sisters Island. Bridges have been proposed for the Three Sisters several times, most recently in the 1960s, when the Three Sisters Bridge proposal led to a decade of protests and ultimately, its cancellation. The Three Sisters are part of the Fall Line, a geologic feature which distinguishes the sedimentary coastal plain of the mid-Atlantic region of the United States from the basement rock of the inland. Part of this basement rock, the Three Sisters are composed of granite. Roughly 300,000 years ago, Atlantic Ocean levels were much higher. At that time, the lower Potomac River was submerged beneath the Atlantic Ocean, whose shores reached the Three Sisters.[ The Potomac River near Washington, D.C., is usually no more than 2 to 4 feet (0.61 to 1.22 m) deep, on average. However, there is a deep channel near the Three Sisters which generally is about 80 feet (24 m) deep, but can drop to just 30 feet (9.1 m) or less during low tide or periods of little precipitation. The rock formation generates sand bars on which grass grows, and these are often visible at low tide. Some sources claim that the Three Sisters represent the farthest navigable point on the Potomac River, although other sources claim that navigability extends farther north to Little Falls Branch. Various legends and historical oral tales are associated with the Three Sisters. Boaters will tell you of the story of the three nuns who drowned there where the three rocks are. This is also the deepest part of the river. One of the earliest stories involves three Algonquian sisters who crossed the river in an attempt to win the release of their brothers, who had been kidnapped by another tribe. They drowned while crossing the river, and were turned into the rocky islets. A less commonly cited legend says three daughters of the local Native American chief were marooned on the islands by their father after rejecting the husbands he picked out for them. The legend holds that the sisters cursed the spot, saying that if they could not cross the Potomac there, no one could. A strange moaning or bell-like sound is said to come from the Potomac River when the curse is about to claim another life. The first European to see the Three Sisters was Captain John Smith, who sailed up the Potomac River and saw them in 1607.[12] The islets were a landmark in colonial times, and appeared on Pierre L'Enfant's first map of the area. -Wikipedia