this is such a good example of flash flooding! cannot tell you how many timea I've had to redirect campers from setting up tents in dru creekbeds for this exact reason. flash flood zones aren't always as obvious as this either. floodplains may look like the perfect, flat, grassy, cool spot by the river to pirch your tent, but they're dangerous! always research where you plan to hike & camp, and always check the weather before you go!