I'm told they're not supposed to, but West Coast USAF fighter pilots DO like to fly the valleys in the high Sierra. Once every few years, someone miscalculates, incurring the inevitably fatal and expensive result.
Once, when hiking at about 8500 feet, we were walking down a valley that T-ed into another, about a half mile away. I happened to be looking at the T when something flashed across the end of the valley, <span style="font-style: italic">well</span> below the peaks. I had more than enough time to think WTF??? as sound travels much slower at that elevation. It was quite the roar when it did get to us, though...