While driving from Dinosaur National Monument to Mesa Verde National Park last year I passed the sight above with the remnants of a hanging flume. The Montrose Placer Mining Company built a 13 mile canal and flume to deliver water from the San Miguel River for gold mining operations. The last 5 miles of the flume clung to the wall of the canyon itself, running along the cliff face in the photo above (see more photos).
Constructed between 1888 and 1891, the 4 foot deep 5 foot 4 inch wide hanging flume carried 23,640,000 gallons of water in a 24 hour period. The mining operations used water and sluice boxes to separate the gold from lighter materials (dirt and gravel).
The technology was not yet available to pump the water directly from the river at the necessary volume and pressure to wash the gold from the gravel, therefore they constructed the flume to transport the water.