The fire was caused by the detonation of a target packed with Tannerite at a gender reveal party in the Coronado National Forest.

The fire was started by accident on April 23, 2017, by Dennis Dickey, an off-duty U.S. Border Patrol agent who had shot the Tannerite target.

When the U.S. Forest Service released footage of the fire's inception in November 2018 at the request of a local news agency, the concept and practice of gender reveal parties became the subject of widespread ridicule and online mockery, a pattern repeated after later wildfires started at such events.

[7] The cause of the fire was a detonation at a gender reveal party hosted by the Dickey family of a target packed with blue dye to indicate the male gender of their child, and Tannerite,[8][9] a highly explosive substance,[10] by Dennis Dickey, an off-duty U.S. Border Patrol agent and the child's father.

[18] That night,[19] the fire crossed and damaged Arizona State Route 83,[20] which runs south through the Coronado National Forest and had been closed earlier that day,[21] and headed east across the Santa Rita Mountains.

[25] By April 25, 363 first responders were fighting the Sawmill Fire,[26] which had grown to 17,000–20,000 acres (6,900–8,100 ha)[27] because of continued low humidity and high winds that made aerial firefighting impossible.

[31] The fire's area nonetheless doubled to 40,356 acres (16,331 ha) and conditions were expected to worsen because of a storm system in northern Arizona.

[15] About 800 firefighters were present and made progress containing the fire with firebreaks on April 28 and 29,[21][32][34] despite aircraft again being grounded by the wind.

[50] Footage of Dickey shooting the target became public when, in November 2018,[9] the Arizona Daily Star acquired it via a Freedom of Information Act request.