There are a lot of variables at play in the catastrophic wildfires currently clawing through southern California: dry vegetation, lack of rain, dense housing development, errant sparks potentially from cigarette butts or campfires or power lines or even arsonists. And then of course there’s gravity. Of all of the factors involved, there may be nothing as basic or as powerful as the tendency of an object with mass to roll or slide or plunge downward under the pull of the Earth below it. [time-brightcove not-tgx=”true”] In the case of the wildfires, the massive object is air—specifically cold air, swirling and flowing 1,200 meters (4,260 ft.) high in California’s Sierra Nevada and White mountains, and the Klamath Basin in southern Oregon and northern California—a whirling of atmospheric dervishes that creates the signature Santa Ana winds.