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
Canning Dam highest and the sixth longest. It is the largest concrete dam in Western Australia in terms of length of crest and volume of concrete. The final cost of the dam was significantly less than had been originally budgeted for, and the work was completed on schedule to a date that was calculated seven years previously. Recently the Canning Dam has been subjected to considerable cracking of the upper parts of the dam and upper gallery. Investigations have shown that cracking was due to strong AAR (alkali aggregate reactivity) in the concrete. AAR results in swelling of the concrete, which may