Course of the Colorado River into the Virgin River, which ran southward through what is now Overton Arm to join the Colorado River near the now-ghost town of St. Thomas, Nevada. At Hoover Dam, the Colorado turns due south through Black Canyon, a direction it will follow for the remainder of its course to the Gulf of California. It passes under the Mike O'Callaghan–Pat Tillman Memorial Bridge (Hoover Dam Bypass), the highest concrete arch bridge in the world, carrying U.S. Route 93 at a height of above the Colorado River. At the end of Black Canyon the Colorado widens into Lake Mohave, created by the
Allegheny River Lock and Dam No. 6 vernacular early-20th century revival style. The locktenders' houses are identical two-story, brick dwellings on concrete foundations. The lock and dam were built by the U.S. Army Corps of Engineers as a part of an extensive system of locks and dams to improve navigation along the Allegheny River. It was listed on the National Register of Historic Places in 2000. Allegheny River Lock and Dam No. 6 Allegheny River Lock and Dam No. 6 is a historic lock and fixed-crest dam complex located at Bethel Township and South Buffalo Township in Armstrong County, Pennsylvania. It was built between 1927 and 1928