Courtesy Avelino Maestas:

Here’s the thing to notice: a bright sunny day, a creek that apparently is normally dry (else the plants alongside would be different), yet look at the muddy chocolate milk thing going on.

Years ago, I was hanging out on a hillside in the backcountry of the Grand Canyon with a group of geologists (I know – rough job, but somebody’s got to do it) when a late summer thunderstorm blew through. It was a gully just like this – completely dry, turned into a mini-torrent. Our problem was that the gully bottom was essentially the only trail back to camp. I still have a pair of formerly white socks stained reddish brown from wading through the water that day.