The cause of death was not immediately clear but there was no evidence of foul play, said Sgt. David Infante of the Los Angeles County sheriff's office.
Mark Landon, among Michael Landon's nine children, appeared in three movies, including "Us" - a CBS television movie written and directed by his father in 1991 just before he died of cancer at age 54. The film was a pilot intended to be another series for Michael Landon. It aired a few months after his death.
Michael Landon also starred in such shows as "Bonanza" and "Highway to Heaven." He adopted Mark Landon after marrying his mother, Dodie Levy-Fraser, in 1956.
Copyright 2009 The Associated Press.
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