Where on Earth? - September 2010

Clues for September 2010:
1. This series of waterfalls began forming 35,000 years ago as sea levels dropped and altered the flow of a river. The river cut into metamorphic rocks, including schists and gneisses, that date to the Precambrian (750 million years ago).
2. In the 1850s, the U.S. Army Corps of Engineers began building a dam near the falls as part of an aqueduct. According to the Army Corps, today the expanded water system produces 180 million gallons of water per day, serving the water needs of more than 1 million people.
3. The waterfalls sit between two U.S. states and are part of a national park.
Name the waterfall and its river.
Scroll down for the answer
Answer: The Great Falls of the Potomac River are located about 24 kilometers west of Washington, D.C., in Maryland near the border with Virginia. In 1853, the U.S. Army Corps of Engineers began constructing a dam near Great Falls for the Washington Aqueduct, which provides water to the residents of the Washington, D.C., metropolitan area. Photo is by Patrick Rodgers.
September winners
Eugene Aleshin (Smithsburg, Md.)
George E. Beetham Jr. (Glenside, Pa.)
Mark Duigon (Baltimore, Md.)
Maria G. Gerber (Clifton, Va.)
Dave Kuentz (Oxford, Ohio)
Bret Leslie (Vienna, Va.)
Debia McCulloch (Lilburn, Ga.)
Diane OKunewick (Idaho Springs, Colo.)
Christopher J. Roll (Gansevoort, N.Y.)
Shuang-Ye Wu (Beavercreek, Ohio)

To submit your photographs to our Where on Earth? contest, send them via e-mail to

23 Sep 2010