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Thank you. It's December 20, 1921, on the Colorado River, the border between Nevada and Arizona.

A small, flat barge rocks in the churning waters as it heads downstream.

Among the men clinging to its wooden sides is John Gregory Tierney, a 36-year-old surveyor. John struggles to keep his balance as the river surges through canyons of orange rock.

He's surprised that the water levels are this high.

It hasn't rained in the region for days, and the land beyond the towering banks of the river

is dry and dusty swath of the American Southwest.

In fact, a need for irrigation is partly what brings John and his crew to this area.

They're searching for the perfect spot to build a dam, one which will control the flow

of the Colorado River, providing hydroelectric power and irrigation for farming and limiting the river's

perilous floods. John believes they're nearing the ideal site, a place where the narrow river

widens into a canyon. It was once known as Devil's Gate, and John can see why. The Black

Mountains loom menacingly over the water on either side, casting deep shadows over the barge.

John manages to resist the current long enough to moor his boat at the riverside.

He hopes to set up camp nearby so his team can survey the area.

But suddenly, the river's roar grows louder.

John looks upstream and sees a rush of water surging toward them.

It must be a flash flood. So John shouts out a warning to his crew. They leap off the barge

onto the shore. But before John can join them, the barge is ripped from its moorings and carried

...