For those of you who lived in dryness-challenged environments, here's how it works with deserts. There's very little rain, so there's very little vegetation. Very little of those means there's very little good topsoil. Very little good topsoil and vegetation means that when it does rain, there's very little capture or absorption of the water. Ergo, when it rains, it floods. When it rains hard, like it has been since yesterday evening, the floods are powerful. How powerful? Well, they can tear away a paved road in minutes, and can flip over a heavy vehicle and send it downstream in seconds.
That's more or less the whole theory. Not complicated, if you think about it for a moment. The thing is, rain storms such as this one don't happen very often (it's a desert), maybe once or twice a decade, depending on size. This one may yet turn out to be even rarer than that: sometimes there are storms of a once-or-twice-in-a-century magnitude. Statistically, by the time a large one rolls in, some folks will have acquired their new SUV in the interval, or they'll be driving a truck they didn't have last time around. Inevitably, some fool will puff up his chest and drive across the roaring water. After all, it's only, what, a few hundred feet? You can see the other side, and it doesn't even look deep. What do you want me to do, sit here and wait 24 hours? I'm a busy man.
Every time there's a storm in the desert, some fool needs the air force to get out of the trouble a six-year-old could have told him not to get into in the first place. If he gets out. In this case, one fellow did, one is dead, and the third is missing. (The video gives only a vague hint of the power, but it's still impressive).