The California family that died in August while hiking in Sierra national forest was killed by heat and probable dehydration, law enforcement officials announced on Thursday, providing some answers to a mystery that had baffled investigators for months. The Mariposa county sheriff’s department believes John Gerrish, 45, his wife, Ellen Chung, 30, their one-year-old daughter, Miju, and their dog, Oski, died on the hiking trail on 17 August. Temperatures were as high as 109F (42.8C) that day, and the majority of the trail has little shade or trees. “Heat-related deaths are extremely difficult to investigate,” said Jeremy Briese, the Mariposa county sheriff. The unusual case had stumped law enforcement since 17 August when officials found the bodies of the family and their dog on a remote hiking trail near the Devil’s Gulch area in Sierra national forest. Their vehicle was located a little more than a mile away, near a gate to the forest. A friend had reported the family, described as avid hikers, as missing. When officials found the bodies, no signs of the cause of death were immediately clear, and the area was briefly treated as a hazmat site. The sheriff’s department described the case as an “unusual, unique situation”. The case transfixed the state and prompting national news coverage as law enforcement and online sleuths sought to determine what happened to the family. In the months since, officials had considered but ultimately ruled out a number of other causes of death, including toxic algae, carbon monoxide, extreme heat, exposure to gas from mines in the area, a lightning strike, suicide and drugs. Water sources in the area where the family was found tested positive for toxic algae. In September, Sierra national forest closed trails near where the family died, citing “unknown hazards found in and near the Savage Lundy trail”. A friend of the family previously told the San Francisco Chronicle that Gerrish was a San Francisco-based software designer who “fell in love with the Mariposa area” and bought several homes there. Gerrish was originally from England, the Fresno Bee reported, and worked remotely for Snapchat while Chung, who was from southern California and had previously worked as a yoga instructor, was in graduate school to become a marriage and family therapist. “From everyone we talk to they were extremely happy, outgoing and loved finding Mariposa, and they were able to work from home and enjoy nature, and in the short time they were here they made a lot of friends,” Briese told the Chronicle.