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.
A Playboy centerfold was ordered to clean up graffiti Wednesday for secretly snapping a photo of a naked 71-year-old woman in a locker room and posting it online with a mocking comment.
Ben Platt had Stephen in tears from the opening song of his Tony-nominated performance in 'Dear Evan Hansen.'
'Wakefield' star Jennifer Garner uses her uncanny salesmanship technique to endorse 'The Stephen Colbert Show' AKA 'The Late Show.'
'Big Brother' host Julie Chen had some surprising news for the reality show contestants who were sequestered during the 2016 election.
Netflix's "War Machine" star Brad Pitt cozies up by Stephen as they contemplate humanity's most puzzling uncertainties.
Stephen is afraid it will be as hard for him to say 'goodbye' as it is for the Press Secretary to say 'the truth.'
President Trump finally got around to addressing one of the biggest threats to America: Stephen Colbert.