Merv Griffin, the entertainment mogul, singer, talk-show host and horseman who has called La Quinta, Calif., home for 20 years, is in grave condition with cancer, according to media reports.“Entertainment Tonight” has reported that sources tell the Hollywood show that Griffin’s prognosis is not good. Griffin’s representatives have not returned calls to The Desert Sun to confirm or deny.Griffin, 82, was admitted to Cedars-Sinai Medical Center in Los Angeles in mid-July after a recurrence of the prostate cancer he battled in 1996 was found during a routine examination.The creator of “Jeopardy!” “Wheel of Fortune” and the host of the iconic “Merv Griffin Show” talk program has kept a 250-acre ranch in La Quinta since he visited the desert with Johnny Carson in 1986 to see Jimmy Connors play tennis.An active desert resident, he has been a supporter of the La Quinta Arts Festival and the owner of the Merv Griffin Givenchy Resort & Spa in Palm Springs, now The Parker. Most recently, he has been the developer of an upscale equine community on a section of his ranch.