Lynn Dianne Olson, known to family as "Dianne," 16, of Salt Lake City, Utah, disappeared on Friday, June 28, 1963, from the GP Bar Ranch, her grandparents' guest ranch at Green River Lakes, about 50 miles northwest of Pinedale in Sublette County, Wyoming. Dianne and her twin brother, Michael, had traveled from Utah to spend the summer working at the ranch, run by their grandparents, Mr. and Mrs. Stan Decker. Around 6:30 p.m. that evening, Michael reported seeing his sister walking across a footbridge at the lakes; she was not seen again. When she failed to return, Sublette County Sheriff Morris C. Horton organized a large search: riders on horseback, search parties on foot (at times up to 60 people a day), aircraft, bloodhounds, and boats on the lake and river. No trace of Dianne was found. On Monday, July 29, 1963 — a month after she vanished — family members found her clothing and eyeglasses folded on a rock about 200 yards from the GP Bar lodge, in an area that had reportedly already been searched. A partially written letter from Dianne to her boyfriend in Salt Lake City was found with the clothing.
The Sublette County Sheriff's Office led the investigation. A Civil Defense scuba diving team based in Cheyenne, Wyoming, dove and dragged the lake twice, reaching depths of 122 feet in clear water with a sand bottom; divers found nothing related to the case. Dianne's mother, Naomi Olson, contacted the FBI and the National Guard for help; FBI Director J. Edgar Hoover replied that the matter fell outside federal jurisdiction, and the National Guard stated it could not act without a request from local civilian authorities, which the sheriff's office did not make. Investigators followed up on reported sightings of Dianne in Idaho, Utah, Colorado, and California in the weeks and months afterward; none were confirmed, and all were determined to be other people. No suspect has ever been identified or charged, and the case remains open. Current Sublette County Sheriff K.C. Lehr has taken a renewed interest in the case and shared surviving case-file materials with a Wyoming news outlet in 2025. Anyone with information is asked to contact the Sublette County Sheriff's Office at 307-367-4378.
