The Hoover Dam — Route 66’s Greatest Detour If you’re driving Route 66 through Arizona, there’s one detour that’s well worth the few extra miles — the Hoover Dam. Built during the Great Depression and finished in 1936, this concrete giant stands over 700 feet tall and still holds back the mighty Colorado River to this day. It's a place where American grit met nature head-on — and won. Thousands of folks traveling the Mother Road take a break to see the dam and feel the breeze off Lake Mead. In t