A family died of "hyperthermia and probable dehydration" in Sierra National Forest on a day when temperatures hit 109 degrees. (Photo: Douglas Klug/Getty)

A Family of Three Died Mysteriously on a Hike. Here’s What Happened.

A couple and their one-year-old child were found less than two miles from their car in the Sierra National Forest, with no obvious trauma. Authorities finally determined the cause of death.

Douglas Klug/Getty

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On October 21, 2021, the Mariposa County Sheriff’s Office announced its long-awaited conclusions about what had killed an active, outdoorsy family and their dog on a hiking trail in California’s Sierra National Forest on August 15. They determined that the family died of “hyperthermia and probable dehydration” on a day when temperatures hit 109 degrees. The cause of death of Oski, an eight-year-old Aussie-Akita mix, remains undetermined. Based on a veterinary examination of the dog’s remains and other evidence on the scene, Sheriff Jeremy Briese said Oski probably also died of heat-related issues.

Software engineer Jonathan Gerrish, 45, his wife Ellen Chung, 31, their one-year-old baby Aurelia “Miju” Chung-Gerrish, and Oski were reported missing by a friend on Monday, August 16, after the family’s nanny showed up for work and found no one at home. Local authorities discovered the four bodies the next morning, just 1.6 miles from the trailhead where the family had parked, on a well-known but remote trail called Savage-Lundy. There were no signs of trauma, or an otherwise apparent cause of death. Chung and Gerrish, who had moved from San Francisco to Mariposa early in the pandemic, were frequent weekend hikers.

The mystery surrounding the family’s death both saddened and captivated people worldwide. Speculation flew on social media, where armchair sleuths hypothesized about everything from poisoning by drug cartels, to a hit by Garrish’s one-time employer, Google. A more promising hypothesis, reported in September by the San Francisco Chronicle, was that the family had been exposed to dangerous anatoxins from algae blooms in the nearby South Fork Merced River (the Sierra National Forest closed the surrounding area as a precaution). The investigation’s toxicology report proved otherwise.

In a press conference, Briese said 30 different agencies aided his office’s investigation, including the FBI. “This is an unfortunate and tragic event due to the weather,” Briese said.

The trail where the Chung-Gerrish family died is an approximately eight-mile loop with more than 4,000 feet of elevation change. It starts at 3,880 feet of elevation, drops down to a river valley at 1,800 feet, and then climbs back out. Hikers typically access it from a dirt road called Hites Cove Road, about 18 miles northeast of Mariposa, at a rudimentary trailhead. There is no cell phone service in the area. Leak Pen, an assistant recreation officer at the Bass Lake Ranger District, which oversees that portion of the Sierra National Forest, described the loop as “steep and challenging and mostly popular during the cooler spring months.”

When the family began their hike at 8:00 A.M. on Sunday, August 15, it was about 75 degrees. The investigation noted that Gerrish’s cell phone showed he had researched the trail the day before using an app, charting out the family’s route. They probably expected to be on the trail for four or five hours, back home in time for a late lunch. They’d packed some snacks, a bottle with baby formula, and an 85-ounce bladder full of water. A common guideline for adult hikers is to drink 16 ounces of water per hour under normal circumstances. Following that math, two people hiking for four hours need 128 total ounces of water. Add in extra for the dog, and to contend with the hot temperatures forecast that day, and Chung and Gerrish probably should have been carrying two 85-ounce bladders. They did not bring a water purifier or a portable dog bowl.

Their hike began with a steep, yet scenic 2.2-mile descent down to the South Fork Merced River, by which time temperatures would have risen by at least 15 degrees, into the 90s. From there, the family trekked parallel to the river for just under two miles. During that time, it’s easy to imagine Oski romping along the riverbank and getting a drink. Perhaps Chung and Gerrish began to worry about their own dwindling water supply. It was searingly hot, over 100 degrees when they reached the hike’s halfway point at the intersection with the Savage-Lundy Trail, which would bring them back to their car.

The app that Gerrish had used to plan their outing wouldn’t have told him that the Ferguson Fire of 2018 had incinerated all the California incense-cedars and pines that used to shade the trail. The tourism site calls the Savage-Lundy “the most difficult trail in the area.” It gains more than 2,000 feet of elevation in its three-mile ascent, on a south/southeast facing slope exposed to constant sunlight. The Chung-Gerrish family only made it up the first two miles. Temperatures for that section of the trail, from 12:50 P.M. to 2:50 P.M., topped out at 109 F. When local authorities found their bodies two days later, the bladder was empty, save for small traces of water.

Extreme hyperthermia, or heatstroke, kills hundreds of people every year. Between 1979 and 2018, there were more than 11,000 heat-related deaths in the U.S. The condition occurs when the body’s core temperature crosses a threshold where it’s unable to cool itself by sweating. According to the Mayo Clinic, the breaking point is about 104 F. Without quick action to lower your body temperature (by finding shade or applying a cold towel, for example), heatstroke causes the brain and other vital organs to swell, which leads to permanent damage and death.

Heatstroke is more common among the very young and very old, but even fit, healthy adults in the prime of their lives—like Chung and Gerrish—can succumb if they’re exerting themselves in high temperatures, like say, 109 F. Especially if they’re dehydrated. While Briese said this is the first hyperthermia death he’s aware of in Mariposa County, in his 20 years of service, it’s not uncommon in other parts of California. This past summer, there were multiple hiker deaths recorded in places like Utah’s Zion National Park and California’s Death Valley. As the planet continues to warm, heatstroke will become an even greater threat.

Still, those who perhaps aren’t familiar with the terrain and temperatures in this section of the Sierra Nevada range are having trouble coming to terms with the investigations’ conclusion. “I’m sorry but I call BS. How do 3 individuals die from hyperthermia simultaneously. Furthermore, the adults were experienced hikers. The dog did not follow animal instincts and seek out water, just laid down and died next to its owners? . . . It makes no sense,” Kara Shearer, a real estate agent on California’s northern coast, wrote on Facebook in response to the Mariposa County Sheriff’s Office’s press release. Many others echoed her sentiment in posts of their own.

But a closer look at the trail, coupled with some local knowledge and intel gleaned from the investigation, demonstrates exactly how it happened.

The families of Chung and Gerrish made a statement following the announcement, thanking the Mariposa County Sheriff’s Office. “Questions have been answered and we will use the information as a way of helping us come to terms with the situation,” the statement read, “however the question ‘why’ can never be answered and will remain with us.”

Lead Photo: Douglas Klug/Getty