FLAGSTAFF, Ariz. (AP) — A video released by the U.S. Forest Service shows how a gender reveal event led to a costly wildfire in southern Arizona that forced about 200 people out of their homes.

The information gleaned from the video isn't new, but it's the first public visual of how quickly the tall, dry grass on state land near Green Valley went up in flames after an off-duty U.S. Border Patrol agent fired a rifle at a homemade target. The rectangular target with a diamond checkered design marked with "boy" or "girl" explodes, sending a blue substance in to the air.

A person whose identity wa...