Orange County officials are looking into the mysterious rocks that set a San Clemente woman's cargo shorts ablaze after her children collected them from San Onofre State Beach.
Preliminary field testing of the seven orange and green rocks showed two had phosphorus on them, according to Orange County Health Care Agency spokeswoman Deanne Thompson.
A naturally occurring mineral, phosphorus is found in oxidized form in rocks, but in its pure elemental form can burn when exposed to air. Phosphorous compounds are used in items from flares to fertilizer.
Thompson said preliminary testing on the rocks was done Sunday. The rocks were sent to a state laboratory to confirm the initial finding of phosphorus – a process that Thompson said could take two weeks.
Geologist Walt Lombardo said the rocks could create a spark, but it's impossible that they would spontaneously ignite on their own.
He guessed that some kind of military material was involved, but it's still not clear exactly what caused the blaze.
"There is phosphorus that naturally occurs on the sand at the beach, but no one has ever heard of pants catching fire," Stone told the Orange County Register.
The 43-year-old woman, whose name was not released, pocketed the rocks that had been picked up from the popular beach, which is known locally as "Trestles" and is not far from San Onofre Nuclear Generating Station and the Camp Pendleton Marine base.
When she returned home, her shorts were set on fire, and they continued to burn the wood floor of her Avenida Estrella home, according Capt. Marc Stone of the Orange County Fire Authority.
"Her pocket just caught on fire. I don't know what happened," her husband said in a 911 call after the blaze was put out. "Her leg is burned. We've got the fire out."
A neighbor said the fire burned through the floor of the family's home.
Stone said that by the time firefighters arrived, the woman's husband was spraying her down with a garden hose. The house was smoky enough to set its fire alarms off, firefighters said.
The woman was hospitalized at Western Medical Center in Santa Ana with third-degree burns to her right thigh and knee, Stone said.
The victim had "stopped, dropped and rolled" in an effort to douse the flames, and her husband suffered second-degree burns to his hand as he tried to help, Stone said. The victim remained hospitalized today, Stone said.
About 20 miles off the coast near San Onofre State Beach is San Clemente Island, which is owned by the U.S. Navy and is its only remaining live firing range, according to a Navy website. The island has been the site of rocket tests.
Pendleton spokesman Capt. Barry Edwards says there's no evidence that material from training exercises was involved, but the base will cooperate if county authorities ask for assistance.
The Associated Press contributed to this article.