The dam stands in Black Canyon on the Colorado River, about thirty miles south-east of Las Vegas, on the border between Nevada and Arizona. It is the most-taken day trip from the city and the one most often described wrongly.
The common error is the drive. Through traffic has not crossed the top of the dam since October 2010, when a bypass bridge opened downstream. Older accounts that describe following the highway over the dam wall are describing a road that no longer carries it.
The Mike O'Callaghan–Pat Tillman Memorial Bridge opened to vehicles on 19 October 2010 and carries US 93 and Interstate 11 across Black Canyon, its roadway some 890 feet — about 270 metres — above the river. It replaced a stretch of highway over the dam crest that was known for hairpin bends and blind curves.
The dam is still reachable. Visitors turn off and park on the Nevada side, and it is possible to drive across the crest into Arizona after a security inspection — but the road is a dead end, with no way to rejoin the highway from the far side, so the return is back the way it came.
The bridge carries a footway, reached by steps or a ramp from the car park on the Nevada side, and it gives the elevated view of the dam that appears in most photographs taken since 2010. It costs nothing, and for anyone not taking a tour it is the best thing at the site.
The longer tour is sold only in person at the site, on the day, and it sells out. Numbers are limited, pushchairs and motorised wheelchairs cannot be taken on it, and knives of any kind — pocket knives included — are not permitted in the buildings. Current times, charges and booking arrangements are on the Bureau of Reclamation's own site, usbr.gov.
It was built between 1931 and 1936, through the worst of the Depression, as a concrete arch-gravity dam wedged into the narrowest point of the canyon: roughly 726 feet — about 221 metres — from foundation to crest. It generates hydroelectricity for Nevada, Arizona and California, and it created the reservoir behind it.
At the groundbreaking in September 1930 the Interior Secretary, Ray Lyman Wilbur, announced that the structure "shall be called the Hoover Dam" — Herbert Hoover being the sitting president and having had a hand in authorising it.
After Hoover lost the 1932 election, the incoming Interior Secretary, Harold Ickes, issued a memorandum in May 1933 directing the Bureau of Reclamation to use Boulder Dam instead, and every official reference duly changed. When President Roosevelt dedicated the structure in 1935, he dedicated Boulder Dam. The original name was restored by Congress in 1947 without a dissenting vote and signed into law by President Truman that April.
The practical consequence is that anything written or printed between 1933 and 1947 calls it Boulder Dam, and both names appear on maps and in books of that period.
The reservoir has its own page — Lake Mead — and its level matters here, because what the dam can generate depends on how much water stands behind it. The lake fell to its lowest level on record in August 2026, and the elevations at which generation is curtailed are set out on that page.
About thirty miles south-east of the Strip, reached on US 93 through Boulder City, and roughly three-quarters of an hour each way without traffic. It combines naturally with Lake Mead, which begins immediately behind it. General practicalities for the city are on the Las Vegas page.