For two months, a family’s hiking trail death was a mystery. Officials now say it was hyperthermia.

For more than two months, California authorities could not say what killed a young family of three and their dog along a hiking trail in the Sierra National Forest.

The bodies of John Gerrish, Ellen Chung and their 1-year-old daughter, Miju, were found close to the Merced River with no physical wounds or signs of trauma. Baffled investigators ruled out a number of possibilities, from lightning to carbon monoxide exposure and toxic algae. Now they have an answer: hyperthermia and possible dehydration, Mariposa County Sheriff Jeremy Briese announced Thursday.

The family had hiked a steep incline with little shade at temperatures reaching up to 109 degrees, possibly running out of water at some point during the trip, Briese said. Investigators believe their dog Oski died of heat-related issues.

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Briese explained hyperthermia is a condition when body temperatures reach an abnormally high level.

“This is an unfortunate and tragic event due to the weather,” Briese said.

Mariposa County Sheriff Jeremy Briese on Oct. 21 said that John Gerrish, Ellen Chung, their daughter Miju and dog died from heat exposure during a remote hike. (Reuters)

In a statement, the Gerrish and Chung families expressed “pain almost beyond words” amid a void of answers during the investigation.

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

The cause behind the mysterious deaths of the family was determined after a litany of tests, including autopsies and toxicology reviews. The sheriff said a team of detectives had worked on the case “round-the-clock,” methodically reviewing evidence like cellphone data and more.

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Gerrish, 45, Chung, 30, and their daughter and dog were discovered after a family friend had reported them missing on Aug. 16. Miju’s babysitter had alerted family members that Gerrish and Chung were not home that day. The day before, a witness saw the family traveling toward the trailhead.

Law enforcement combed the trail after spotting the couple’s truck parked near the trail’s entrance, The Washington Post previously reported. Later that morning, in an area known as Devil’s Gulch, search-and-rescue officers discovered Gerrish in a seated position with Miju and Oski near him, while Chung was found farther up a hill.

Authorities later closed the 28 miles along the river the family was found near after test results of the water downstream revealed high levels of toxic algae — but algae blooms were ruled out as a cause of death. The family did not drink the water from the river, Briese said.

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The sheriff said investigators also considered possible exposure from nearby mines, but they determined the family did not visit those mines.

The loss of the young family came as a shock to those in the Mariposa community who knew them.

“It’s just so tragic and mysterious,” Steven Jeffe, a close family friend, previously told The Washington Post.

The couple moved to Mariposa from San Francisco in March 2020. Gerrish worked at Snapchat, and Chung was working toward a master’s degree in family therapy, Jeffe said.

Those who knew the couple described their love of outdoor adventures and hiking, questioning what could have happened during their trip to Hites Cove.

“We’re just devastated by the loss,” Jeffe said. “But I think the community is more like, ‘What the heck happened?’ It’s just so crazy.”

On Thursday, Briese showed footage of the eight-mile trail the family had nearly completed, with sloping terrain that had little tree cover due to a wildfire in 2018. They were 1.6 miles away from completing the hike.

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A sole container for water found with the family, an 85-ounce water bladder backpack, was empty.

Briese said he has not encountered another hyperthermia death during his work at the sheriff’s office. But he warned others to take precautions when outdoors during sweltering summers.

“My message would be to prepare, if you’re going to hike, prepare,” he said.

The Gerrish and Chung families said they would use the new revelations “as a way of helping us come to terms with the situation.”

“However,” they added, “the question of why can never be answered and will remain with us.”