 It's a bright summer day in the mountains. Research geologist Andrew Manning and some colleagues are hauling sensors, buckets, and other scientific equipment through thick scrub willow at the edge of a rushing mountain stream. We are on the Upper Snake River in the Colorado Rockies here at about 11,000 feet. The Upper Snake doesn't look like a clear mountain stream. Instead, it has a distinct reddish hue. That's because the water is depositing iron onto the riverbed.