A friend of adult film star Marilyn Chambers says the actress has been found dead at her home in northern Los Angeles County.

Peggy McGinn says the 56-year-old Chambers was found by her 17-year-old daughter Sunday night and the cause of death has not been determined.

Chambers starred in the 1972 film "Behind the Green Door," which was more widely distributed and attracted a more mainstream audience than the usual adult fare.

Chambers, whose given name was Marilyn Briggs, was once a model for Ivory Snow. She was among the first porn superstars when the stag films of the 1940s through 1960s gave way to the more polished sex films of the 1970s.