MARIPOSA COUNTY (CBS SF/AP) — A young Northern California family who was found dead after going on a hike in Sierra National Forest were killed by hyperthermia and possible dehydration after walking for hours in triple-digit heat.

John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Miju, and their dog were all found dead on a hiking trail Aug. 17 after a family friend reported them missing after they went hiking along Hites Cove Trail just south of state Highway and about 20 miles west of Yosemite National Park.

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The temperatures in the area were between 107 and 109 degrees along a steep trail that had no shade, and the family had been carrying only one 85-ounce water container, less than 3/4 of a gallon, which was empty Mariposa County Sheriff Jeremy Briese said during a Thursday afternoon press conference.

Family Found Dead in Sierra Nat'l Forest

John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Miju, and their dog were all found dead on a hiking trail near Hite’s Cove in the Sierra National Forest. (CBS Fresno via YouTube)

The temperature when they started the hike at 8 a.m. was 79 degrees. The cause of death of the family’s dog was undetermined, but it’s believed the dog was also suffering from heat-related issues.

The family was found dead along Savage-Lungy Trail, adjacent to the Hites Cove Trail, just 1.6 miles away from their vehicle.

According to Fresno CBS affiliate KGPE-TV, Gerrish was from the United Kingdom and met Ellen Chung in San Francisco before they relocated to Mariposa during the pandemic in 2020.

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Mariposa County Sheriff’s investigators have worked with toxicologists, environmental specialists, the FBI and other experts. They had already ruled out the causes being related to a gun or any other weapon, extreme heat, a lightning strike, carbon monoxide, carbon dioxide, cyanide exposure, illegal drugs, alcohol or suicide.

“From the beginning, the Gerrish and Chung family have been our top priority as we’ve dealt with this horrible event, and our office has dedicated an entire team to this case and we have partnered with over 30 local, state and federal agencies,” said Briese.

The deaths led the Bureau of Land Management to close campgrounds and recreation areas along 28 miles (45 kilometers) of the river, between the towns of Briceburg and Bagby, when water samples downstream from where the family died showed high levels of toxic algae.

Briese said the family did not drink water with toxic algae, and there was no evidence they accessed any mines.

“We do not have any evidence indicating that Jonathan, Ellen or Miju ingested any of that water.”

Toxicology reports all came back negative for any prescription or illegal drugs, he said.

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