The mysterious deaths of John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Miju, and their dog baffled authorities for two months.
"Hyperthermia is abnormally high body temperature caused by a failure of heat regulating mechanisms. So in general, the more severe hyperthermia is heat," Sheriff Jeremy Briese explained. "Body temperatures, when they become over 105 degrees, can have damages to the brain and other organs and cause muscle cramps, fatigue, dizziness, weakness, and ultimately cause the very person to die."
The family went hiking on a trail close to the Merced River in the Sierra National Forest, where they were found dead Aug. 17 after a family friend reported them missing.
Briese released a timeline of events that investigators pieced together. He said Gerrish plotted out the family’s hike on an app on his phone, but it did not show elevation changes. The FBI is still examining the phone for clues.
Briese said the family began their hike on Aug. 15 around 8 a.m. with temperatures in the 70s. They walked about 2.2 miles to another trail where the elevation dropped and temperatures rose to between 92 and 99 degrees. They continued for another 1.9 miles with temperatures between 99 to 103 degrees.
The family reached a trail with that was constantly exposed to sunlight due to the Ferguson Fire of 2018. It was the noon hour and temperatures were between 107 to 109 degrees.
Investigators found an empty water backpack near the family. The family did not have a water filtration system according to officials. They were about two miles away from a trail that had access to the river. Investigators also found a small amount of formula, a bottle, and snacks.
"The terrain, lack of shade, lack of water…once we got all that together… it all clicked," Briese said.
Mariposa County Sheriff’s investigators have worked with toxicologists, environmental specialists, the FBI and other experts. They have already ruled out the causes being related to a gun or any other weapon, a lightning strike, carbon monoxide, carbon dioxide, cyanide exposure, illegal drugs, alcohol or suicide.
Briese said water samples taken from the area did show toxins, but there was no evidence that the family had ingested that water.
The deaths led the Bureau of Land Management to close campgrounds and recreation areas along 28 miles 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.
Part of a statement from the Gerrish-Chung families read in part: "Our hearts will never forget the beautiful lives of Jonathan, Ellen, Miju and Oski. They will remain with us wherever we go and whatever we do."