Originally named Boulder Dam, Hoover Dam remains one of the greatest engineering achievements in the 20th century. Initially planned for a site 10 miles from today’s dam, engineers and geologists re-examined field data after the St. Francis Dam disaster on March 12, 1928. Built to supply Los Angeles with water, the San Francisquito Canyon Dam burst on it initial filling, killing at least 450 people, destroying 1,000 homes, knocking out bridges and power lines, and ranking second among California’s disasters.
     Faced with a series challenges and logistical nightmares, design work began on the Hoover Dam in 1921. One of the most ambitious undertakings in the early 1900s, Six Companies (a joint venture), took on the task of boring four diversion tunnels through solid rock, removing the loose face rocks from Black Canyon cliffs, building a new city for thousands of workers, chilling 3.25 million cubic yards of freshly poured concrete, and keeping a ‘round-the-clock operation on track.
     Today, nearly a million visitors take the tour of Hoover Dam every year, and many more drive across the dam over U.S. Route 93. Here, the Colorado River marks the border between Arizona and Nevada. This view also captures a glimpse of a new construction project, the Colorado River Bridge. The Hoover Dam Bypass project utilizes another engineering marvel, a twin-ribbed concrete arch bridge spanning Black Canyon.