Image source, CBS

A California sheriff has said heat and possibly dehydration are to blame for the deaths of a family found on a remote hiking trail in August.

Jonathan Gerrish, 45, Ellen Chung, 30, their one-year-old girl Aurelia Miju Chung-Gerrish and dog Oski died due to hyperthermia in Devil's Gulch Valley.

The announcement comes over two months after rescue crews found their bodies in the Sierra National Forest.

Their unexplained deaths had puzzled summer hikers in the US West.

In a news conference on Thursday, the Mariposa County Sheriff's Office said that the family had been found with an empty 85oz (2.5-litre) water bladder, and did not have any other bottles or water filters with them.

Temperatures on the day of their hike rose above 109F (42C), officials say.

According to CBS News, the BBC's partner in the US, Mr Gerrish was from the UK and met Ms Chung in San Francisco before moving to the small town of Mariposa in 2020.

Their bodies were discovered by rescue crews on 17 August in an area south-west of Yosemite National Park after a friend called authorities to report them missing.

The Mariposa County Sheriff's Office has been working with FBI, environmental researchers and toxicologists to determine what killed the family.

They had already ruled out death by lightning, carbon monoxide, carbon dioxide, cyanide, illegal drugs, alcohol, gun "or any other type of weapon" or suicide.

The FBI is still attempting to access the mobile phone owned by Gerrish, Mariposa County Sheriff Jeremy Briese told reporters.

He added that there is no phone service in the area where they were hiking, and that an earlier fire had burned trees that would normally provide shade in some sections of the steep trail.

Concerns over water quality in the nearby Merced River led to speculation that an algae bloom could have killed them, but officials say there is no evidence that the family drank the river water.

Other dismissed theories included a leak that originated from abandoned gold mines that are common in the Gold Rush region.