Every day, about 430 million gallons of water enter Los Angeles from the eastern slopes of the Sierra Nevada Mountains.

The journey begins in the sky, when rain and snow fall on the mountainside; water then flows into the Owens River and travels a human-built route for the next 200-plus miles.

Pipes, tunnels, and canals—all mapped out a century ago—navigate hills, valleys, and desert terrain en route to North America’s third-largest city.