Question: Which canal was in operation most recently, the Chesapeake and Ohio Canal or the Blackstone Canal?
Context: Four Locks is a former small community which is now part of the Chesapeake and Ohio Canal National Historical Park.  It was once a thriving community of homes and businesses in Washington County, Maryland that supported the Chesapeake and Ohio Canal from the mid-19th century, until its closure in the 1920s.  In its heyday, the small community consisted of two stores, two warehouses, a dry dock for boat repair, a school, and post office, plus about a dozen houses. The Blackstone Canal was a waterway linking Worcester, Massachusetts, to Providence, Rhode Island (and Narragansett Bay) through the Blackstone Valley via a series of locks and canals during the early 19th century. Carderock Recreation Area is a 100-acre park in Carderock, Maryland, part of the Chesapeake and Ohio Canal National Historical Park.  Area is well known as a destination for its outdoor activities like rock climbing, hiking and biking.  It is bounded by Potomac River on the South and Chesapeake and Ohio Canal on the North border and it is accessed from Clara Barton Parkway from the same exit as Carderock Division of the Naval Surface Warfare Center. The Chesapeake and Ohio Canal, abbreviated as the C&O Canal and occasionally called the "Grand Old Ditch," operated from 1831 until 1924 along the Potomac River from Washington, D.C., to Cumberland, Maryland.  The canal's principal cargo was coal from the Allegheny Mountains. Power Plant and Dam No. 5, also known as Honeywood Dam, comprises a dam on the Potomac River, originally built for the Chesapeake and Ohio Canal, and a power plant built to take advantage of the river's flow to generate hydroelectric power.  The dam is included in Chesapeake and Ohio Canal National Historical Park. The Chesapeake and Ohio Canal Association is a not-for-profit organization that supports the Chesapeake and Ohio Canal National Historical Park.  Its charter states that the association is "concerned with the conservation of the natural and historical environment of the C&O Canal and the Potomac River Basin." Blackstone River Valley National Historical Park is a National Park Service unit in the states of Rhode Island and Massachusetts.  The park was created for the purpose of preserving, protecting, and interpreting the industrial heritage of the Blackstone River Valley and the urban, rural, and agricultural landscape of that region.  The Blackstone River Valley was the site of some of the earliest successful textile mills in the United States, and these mills contributed significantly to the earliest American Industrial Revolution.  The subsequent construction of the Blackstone Canal, a few years after the successful completion of the Erie Canal, helped to sustain the region's industrial strength. The Chesapeake and Ohio Canal commemorative obelisk is an 8 ft marble obelisk erected in 1850 in Washington, D.C., to mark the completion of the Chesapeake and Ohio Canal to Cumberland, Maryland.  It stands on the northwest corner of the Wisconsin Avenue Bridge over the canal in Washington's Georgetown neighborhood. Bear Island is an island located in Potomac, Montgomery County, Maryland between the Potomac River and the Chesapeake and Ohio Canal near the Great Falls.  It is managed by the National Park Service as part of the Chesapeake and Ohio Canal National Historical Park and is co-owned by The Nature Conservancy.  One of its most popular attractions is the Billy Goat Trail.  Pets are not allowed on Bear Island, nor is smoking. The Cumberland Dam was built across the North Branch of the Potomac River at Cumberland, Maryland, for the purpose of diverting water of the river into the head of the Chesapeake and Ohio Canal.  The Chesapeake and Ohio Canal Company began construction of its Dam No. 8 in 1837 and work proceeded intermittently, finally concluding in 1850.  The dam impounded water over a distance of a mile, causing back water for about 3 mi up the river.  Above the dam is the mouth of Wills Creek.
Answer: Chesapeake and Ohio Canal