Mariposa County Sheriff Jeremy Briese announced the cause of death of Jonathan Gerrish, Ellen Chung, their one-year-old daughter Aurelia Miju Chung-Gerrish and their companion dog Oski at a press conference Thursday after- midday.
Sheriff Briese said Mr. Gerrish made an eight mile loop along the Hite Cove Trail on a hiking app on August 14.
The family then set off early the next morning.
Sheriff Briese said the family had walked for miles under “constant sunshine and very little shade” with temperatures reaching 109 F (42 C).
Their bodies were discovered along the Savage-Lundy Trail on Aug. 17 just 2.5 km from their vehicle, he said.
Mr. Gerrish was found sitting on the trail with Miju and Oski next to him while Ms. Chung was found further down the trail.
There was no cell phone reception where the family was found, he said.
Sheriff Briese said an empty 85-ounce water bladder backpack was found next to the family when they were found, but they had no other water containers with them at the time.
They also carried snacks and bottles containing formula.
The family had completed most of the route when they succumbed to the heat, he said.
The sheriff also showed a video at the press conference illustrating the terrain and the high elevation of the trail.
The family’s babysitter sounded the alarm on August 16 when she arrived for her regular shift at their house and found they weren’t there.
Search and rescue teams first found the family’s vehicle before finding their bodies shortly after.
For the next two months, the case baffled authorities and the cause of their death remained a mystery.
“When we located the family, there was no apparent cause of death,” Sheriff Briese said Thursday.
During the investigation, multiple causes of death were ruled out, including: suicide, being caused by a gun or other weapon, alcohol, illegal drugs, lightning, heat extreme exposure and exposure to cyanide, carbon monoxide or carbon dioxide.
One theory that remained was that they had been killed by toxic algae found in nearby water and investigators had worked with toxicology experts to determine if the high levels of toxicity could have plagued the family.
Sheriff Briese confirmed that these tests confirmed the presence of toxic algae in the water, but said there was “no evidence that they drank this water.”
The area around the trail was also known to contain mines.
Sheriff Briese said a mine was also located near where the family were found, but there was no evidence the family came into contact with them.
He added that what had happened was “an unfortunate and tragic event due to the weather”.