A British-born software engineer, his wife and their one-year-old baby, whose deaths while hiking in California left investigators mystified, are likely to have died from hyperthermia and dehydration.

Investigators say they believe Jonathan Gerrish, Ellen Chung and their one-year-old daughter Aurelia Miju Chung-Gerrish died as a result of extreme heat in the Sierra National Forest in August.

They were found by search and rescue teams on a remote trail a day after being reported missing.

Their dog Oski was also found dead nearby.

Investigators had already ruled out that they had been killed by any weapon or taken their own lives.

There was also no sign they had been struck by lightning or exposed to any poisons or substances.

In revealing the likely cause of their deaths, the Mariposa County Sheriff Jeremy Briese revealed officers had found an empty CamelBak water bladder backpack near the family but no sign of any other water supply.

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At times along sections of their planned hike, he said, the temperatures could have reached 42C (109F) with very little shade.

Mr Gerrish, 45, was originally from Lancaster and had moved to California to work for Google and Snapchat in Silicon Valley.

Ms Chung, 30, a family therapist, was born and raised in California.

The couple had moved to rural Mariposa County from San Francisco at the start of the lockdown in March 2020.

In a statement the Gerrish and Chung families said: “The loss of a close relative is a pain almost beyond words.

“When that loss is multiplied by four and one of that four is a baby of just one years old, then the pain is indescribable.

“When that pain is then further impacted by the lack of knowledge and certainty as to the reasons for their deaths, then the questions of why, of where, of when and of how, fill your mind all of the days and all of the nights.

“Some questions have been answered and we will use the information as a way of helping us come to terms with the situation, however the question ‘why’ can never be answered and will remain with us.

“Our hearts will never forget the beautiful lives of Jonathan, Ellen, Miju and of course Oski.

“They will remain with us wherever we go and whatever we do.

“In the future, when we sit beneath the trees listening to the wind soughing through the branches we will hear them and we will remember.”

Last month a section of river close to where the family was found was closed over concerns that a toxic algae bloom had led to high levels of potentially fatal anatoxin in the water.

Although some toxicology results are still pending, the sheriff said multiple laboratory tests showed the family did not ingest any of the contaminated water.

The possibility of a gas leak from an abandoned gold mine in the area was also ruled out.

Hyperthermia can occur when the body’s heat-regulating mechanism can no longer deal with the heat from the environment, causing an abnormally high body temperature.

“Heat related deaths are extremely difficult to investigate, and I want to thank you all for being patient with us as we investigated this case,” said Mr Briese.

“As I’ve mentioned, the Gerrish-Chung family have been our top priority as we dealt with this horrible event.”

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