LOS ANGELES (AP) - A couple's plan to reveal their baby's gender went up not in blue or pink smoke but in flames when the device they used sparked a wildfire that burned thousands of acres and forced people to flee from a city east of Los Angeles. 

The fire prompted evacuations in parts of Yucaipa, a city of 54,000, and the surrounding area. Water-dropping helicopters were brought in but the fire has proven stubborn - it grew to 11.5 square miles (30 square kilometers) by Monday morning and more than 500 firefighters on the scene only had minimal containment. No homes have burned and no injuries reported. 

It's the latest in what has become a lengthy list of tragedies at events where typically smoke, confetti, balloons or other colored objects are used to reveal the soon-to-be-born child's biological sex - pink for girls and blue for boys. Sometimes the made-for-social-media gatherings are spectacles and include explosives and even guns, and at least one had deadly consequences. 

The fire started Saturday morning at El Ranch Dorado Park, a rugged natural area popular with hikers and dog owners. In summer the park's tall natural grasses dry out and turn golden, and when combined with the San Bernardino Mountains in the distance, provide a popular backdrop for family photos and videos.

The unidentified couple chose the location to reveal their baby's gender. They were accompanied by their young children and had a friend or relative videoing on a cell phone, said Capt. Bennet Milloy of the California Department of Forestry and Fire Protection.

The family went into a field and fired off the device, which quickly ignited 4-foot (1.2 meter) grasses, Milloy said. Conditions were perfect for a fire to spread quickly - triple-digit temperatures, low humidity, dry vegetation and a stiff breeze.   

Surveillance video showed the couple frantically race to their vehicle to retrieve water bottles to try to extinguish the flames. It was futile and they called 911. 

"You can't fight a fire like this with a water bottle," Milloy said. "They had no chance after it started."  

Firefighters arrived within minutes and the distraught couple told them what happened and provided their own photos and video to aid the investigation, Milloy said. 

"It's a pretty tragic situation," he said. "Obviously this was supposed to be a happy event."

The couple could be liable for the cost of fighting the fire and criminally charged with misdemeanor or felony counts.  

In 2017, a massive Arizona wildfire was accidentally started by an off-duty Border Patrol agent who shot a target filled with an explosive blue powder. The fire burned 47,000 acres (73 square miles) and caused $8 million in damages, Agent Dennis Dickey was charged with a misdemeanor and sentenced to probation.

Last year, a homemade explosive used to reveal a baby's gender killed 56-year-old Pamela Kreimeyer in Knoxville, Iowa. The device was meant to spray powder but instead blew up like a pipe bomb. Kreimeyer, who was standing 45 feet (13 meters) away, died instantly when debris struck her head.

Milloy said some devices used to reveal genders are harmless but others contain chemicals that produce heat and can spark fires.   

He said the device used Saturday will be tested to determine what it contained. Milloy didn't know the color it emitted.

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