In in the next day scramble to figure out what exactly caused two Marine helicopters to collide on the California-Arizona border, at least one theory has emerged, and it involves dust.  On Wednesday night, Cobra and Huey helicopters ran into each other in midair near the Marine base in Yuma, Arizona during what was described as a "routine exercise." Gunnery Sgt. Dustin Dunk suggested to CNN that visibility may have been affected by a "brown out" caused by dust kicked up by the helicopters. Marine Corps spokeswoman 1st Lt. Maureen Dooley told CNN, "We won't know exactly what happened until the investigation is complete."

In the meantime, KTVK in Phoenix has footage of the wreckage, shown above. The military is waiting to release the names of the seven killed Marines until their families are informed.