Floods are common this time of year in the Southwest, but the deadly flash flooding at the Grand Canyon on Saturday was fueled by a unique combination of factors. The annual monsoon season brought moisture from the Pacific Ocean to the region, and heavy rain fell over a rocky, impermeable landscape, causing water to rush downhill quickly. At least two people died as the surge swept through Bright Angel Canyon.

Meteorologists noted that while the amount of rain was not extreme, its intensity and the terrain made it particularly dangerous.