<human>:  When was the Hoover Dam built?
<bot>: The Hoover Dam was built between 1931 and 1936. It was the largest dam in the world at the time. The dam is located on the Colorado River, which runs through the states of Arizona, Nevada, and California. The dam was built to provide hydroelectric power for the region, and it has helped to make Las Vegas one of the most popular cities in the world.