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Investigative report into Mariposa family who died on a hike lays out a shocking timeline of catastrophic missteps

For two months, Mariposa County investigators looked for algae-laden water, long-lost mines that might emit toxic gas, poisonous vegetation, evidence of lightning strikes — anything that could explain how a young family and their dog mysteriously died together this summer on a remote trail near their home.

But in the end, as detailed in 77 pages of investigative reports obtained by The Chronicle, detectives kept coming back to sizzling hot temperatures, lack of shade, rigorous terrain and a slew of disastrous choices that led to the shocking deaths of Ellen Chung, 31, and Jonathan Gerrish, 45, along with their 1-year-old daughter, Miju, and dog, Oski, after an Aug. 15 hike.

The family, numerous experts told the detectives, appeared to catastrophically underestimate just how dangerous their trek would be with temperatures reaching 109 degrees on a steep path locals knew to avoid during the summer. Crucially, it appeared they hadn’t brought nearly enough water.

One U.S. Forest Service volunteer who had hiked the nearly 8-mile loop more than a dozen times told a deputy the family appeared “completely unaware of the dangers.”

The records, released to The Chronicle under California public records laws, recount a difficult investigation while offering insight into a tragedy that captivated hiking and outdoors enthusiasts around the world, with many wondering how everything could seemingly go wrong at once, leading to an entire young family and their dog dying together.

The documents also provide new details about Chung, a yoga instructor and graduate student, and Gerrish, a Snapchat engineer, who perished after a pandemic move from San Francisco to Mariposa, where they bought numerous properties and embraced the famed Sierra foothills.

Mariposa County Sheriff Jeremy Briese points to a map to show where the missing family was found dead during a news conference in Mariposa on Oct. 21.

Craig Kohlruss / The Fresno Bee via AP

In October, Mariposa County Sheriff Jeremy Briese closed the case, announcing that the husband and wife and their daughter died of hyperthermia and probable dehydration. They essentially got too hot, causing their brains to shut down, followed by their organs, according to one expert detectives interviewed.

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

The investigation laid out a harrowing timeline that began before the deadly excursion.

The last person to see the family alive was their babysitter on Aug. 13, two days before the hike. The woman — whose name was redacted, as were all names other than Chung and Gerrish in the reports — finished cleaning the house and left that afternoon. Later that evening, she had her final communication with Chung, as the young mother texted the babysitter a video of Miju starting to walk.

It was that weekend when, detectives say, Gerrish used an app to map out the hike. A search of Gerrish’s AllTrails history indicated he had hiked a portion of the same loop in May 2017, in weather that was probably cooler.

The day before the hike, a friend and business associate said he received a text from Gerrish.

“Mate!” Gerrish wrote. “Just been battling through the bush to find the property corners so much fun.”

Gerrish had been finding the boundaries of his new properties, said the man who helped manage the family’s construction projects. The couple had bought four homes in the area, some already rented out as Airbnbs. They were protective of their young daughter, the man told detectives, and at one point asked him to make their daughter’s bedroom cooler because it was “too stuffy.”

At about 7:45 a.m. on Aug. 15, a woman walking her dogs along a narrow dirt track, Hites Cove Road, saw the family’s gray Ford F-150 Raptor drive past and park at the trailhead.

The temperature was 76 degrees. Within three hours it would soar to 99 degrees, and by the afternoon it would peak at 109. The ground temperature would have been higher, investigators said, particularly since the 2018 Ferguson Fire burned off any tree canopy that would have provided shade.

Gerrish wore dark shorts, a yellow T-shirt and tennis shoes. Chung wore brown hiking boots, spandex shorts and a yellow tank top. The baby, dressed in a short-sleeved onesie and pink shoes, was strapped into a children’s backpack on Gerrish’s back.

The dog was an Aussie-Akita mix, with its partial cold-weather breeding giving it a thick coat and making it more susceptible to heat, experts said.

There is no indication anyone saw the family on the trail.

Mariposa County authorities believe Ellen Chung, 31, Jonathan Gerrish, 45, their 1-year-old daughter Miju and dog Oski went on an Aug. 15 hike on the Hites Cove Trail loop before perishing as a result of hyperthermia and probable dehydration.

Mariposa County authorities believe Ellen Chung, 31, Jonathan Gerrish, 45, their 1-year-old daughter Miju and dog Oski went on an Aug. 15 hike on the Hites Cove Trail loop before perishing as a result of hyperthermia and probable dehydration.

Provided by Steve Jeffe

The next day, at 11 a.m., the babysitter returned to the couple’s home, a few miles from the trailhead, and found it empty. The couple’s wallets and most of their cell phones were there. Even more confusing to the babysitter, the diaper bag that the couple always brought with them had been left behind.

She called the construction manager, who was not initially concerned because Chung and Gerrish were a “very active family,” a deputy wrote. They started making calls and sending texts. By 5 p.m., they began driving around looking for the family. At 11 p.m., they called the sheriff.

The search did not take long. After the truck was found at the trailhead on the morning of Aug. 17, crews found the bodies of Gerrish, his child and the dog about 1.6 miles below the trailhead, on a series of steep switchbacks of the Savage Lundy Trail.

Gerrish had a cell phone in the front pocket of his shorts. But multiple crime labs have been unable to access the Google Pixel 4 to check for any failed texts or calls on the day of the hike — cell phone coverage is spotty at best along the trail — and the device is still at FBI headquarters.

Investigators initially called a helicopter to the area and said Chung was still missing.

About an hour later, around 10:30 a.m., a deputy walking back up the trail from where Gerrish was found with his daughter and dog noticed “some disturbed dirt on the uphill side of the trail that appeared that something or someone had tried to go up the hill.” He spotted a shoe and then Chung’s body. She was about 13 feet in elevation higher than her family.

At the same time, a Ford key fob was found along the trail, about 100 feet below where Gerrish was found.

Rescuers found no signs of foul play. After spending the night at the scene with the bodies, deputies helped a California Highway Patrol helicopter airlift the family off the trail. They placed the couple’s wedding rings into envelopes for safekeeping, according to the reports.

A deer walks in front of the onetime Mariposa County home of Jonathan Gerrish and Ellen Chung on Aug. 19, 2021.

A deer walks in front of the onetime Mariposa County home of Jonathan Gerrish and Ellen Chung on Aug. 19, 2021.

Tracy Barbutes / Special to The Chronicle

After closing down the trail out of concern the family might have ingested poisonous fumes from an abandoned mine shaft, investigators began interviews — including with the construction manager, who called the couple “city folk,” giving an example of how Gerrish would go to the store and get firewood rather than cutting his own. No one suspected a crime.

Deputies served a search warrant on the couple’s home the same day the bodies were recovered and found more electronic devices, including phones that had missed messages from the previous days.

In the backpack Chung carried on the trail, investigators recovered a snakebite kit, knife, bug spray, first aid kit, extra diapers, an empty sippy cup with remnants of what appeared to be formula, another empty sippy cup and a teething wafer wrapper.

Chung was also carrying a 2.5 liter Osprey Hydraulics LT water bladder with only a “few remaining drops” of water, which detectives tested. They detected no toxins in the water.

Investigators did find two different types of anatoxin-a, a neurotoxin, in the Merced River, which runs adjacent to the bottom portion of the hike. But an expert told deputies the levels were low and that a dog would have to drink multiple liters to die. The expert said that such toxins could kill dogs or livestock but that there had been no known human deaths.

Detectives pored over a map of old mines and pinpointed nothing nearby. They checked the bodies, and even the dog’s metal collar, for burn marks from a possible lightning strike, but struck out again.

All the evidence kept pointing back to heat exposure and lack of water.

Investigators spoke to a U.S. Forest Service employee familiar with the trail who said locals “stay clear” of it during summer months.

A U.S Forest Service volunteer said that on his trips along the trail he often waited at the bottom until the sun set, to make the final steep stretch back up to the trailhead in the shade. For a hike under those conditions, he recommended 320 ounces of water for an adult couple, and 16 ounces each for a baby and dog. Yet the couple apparently carried only 84 ounces of water in total and no water filtration system to gather supplies from the river.

A Modesto doctor who treats extreme heat victims told investigators that once an individual gets heatstroke, they can die within a couple of hours. The moment the family started their hike — with their lack of water and other deficiencies — the “clock was ticking,” the doctor said.

A survival trainer sent detectives an email calling the terrain, elevation and heat a “deadly trifecta.”

He, too, concluded that heat and exertion led to their deaths.

“Sadly, I believe they were caught off guard, and once they realized their situation, they died trying to save their child and each other,” the trainer wrote to detectives. “It is likely the child began to succumb first, which hurried the parents’ efforts up the hill. When one could no longer continue, they stayed behind to care for the child and pet, while the other tried to forge on and get help for their loved ones. It is a tragedy of the highest order.”

Matthias Gafni is a San Francisco Chronicle staff writer. Email: matthias.gafni@sfchronicle.com Twitter: @mgafni