Correction: San Clemente Island lies about 60 miles offshore.
How rocks collected from a southern Orange County beach caught fire in the pocket of a San Clemente woman's cargo shorts, landing her in a hospital with third-degree burns, remained a mystery today.
The 43-year old woman's children picked up the seven orange and green rocks on Saturday at , which is popular with surfers and known locally as Trestles.
The rocks combusted and set the woman's shorts on fire and continued to burn the wood floor of her Avenida Estrella house, according Capt. Marc Stone of the Orange County Fire Authority.
The woman, whose name was not released, was hospitalized at Western Medical Center in Santa Ana with third-degree burns to her right thigh and knee, Stone said. He added that the victim "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.
The Orange County Health Care Agency is running tests on the rocks, but results could be days away, Stone said.
Two of the rocks were found to contain phosphorous, which can burn like a road flare when ignited, but the other five were cross-contaminated while in the woman's pocket, according to ABC7.
The rocks were smooth and some were the size of a hamburger patty, while others were small enough to fit in a coffee cup, according to news reports.
The beach where the rocks were found is not far from the and the Camp Pendleton Marine base. San Clemente Island, which lies about 60 miles off the coast, is owned by the U.S. Navy and is its only remaining live firing range, according to a Navy website. The island has also been the site of rocket tests.