Herbert Hoover was the US Secretary of Commerce in 1934 and later was elected US President. He was a key part in getting the dam built, so, despite its official name being the Boulder Dam, it became known as the Hoover Dam.
The dam is a huge concrete construction built by more than 21,000 workers. It stands 221 metres (726 feet) high and 379 metres (1,244 feet) wide.
There are a couple of reasons why the Hoover Dam was built. Firstly, it helped back up a load of river water to provide liquid to the parched plains of California and Arizona and secondly, the amount of water flowing through the system gets harnessed to create a huge amount of hydroelectric power to the area.
It sits in the Black Canyon, a valley on the Colorado River.
After years of planning, building began in 1930 and it was completed five years later. President Franklin D. Roosevelt officially opened it on 30 September.
Dynamite was used to blast out diversion holes for the mighty river to flow through. The river bed was excavated and a massive concrete arch was constructed. There was an incredible 3.25 million cubic yards of concrete used. The diversion tunnels were closed and the run-off Lake Mead was created from the overflow.