According to USA Today,

A California family of three found dead in August died of hyperthermia and probable dehydration, Mariposa County Sheriff Jeremy Briese confirmed. 

The cause of death comes almost two months after John Gerrish, Ellen Chung and their 1-year-old daughter, Miju, were found dead on a hiking trail near the Merced River in the Sierra National Forest.

The family dog’s, an 8-year-old Aussie/Akita mix named Oski, death hasn’t been determined, but Briese said it’s likely it was also heat-related.

“This is an unfortunate and tragic event due to weather,” Briese said at a press conference Thursday afternoon. “If you’re going to hike, prepare appropriately.”

Hyperthermia is when the body becomes too hot while in extreme conditions and cannot regulate heat, with body temperatures exceeding over 104 degrees Fahrenheit, according to the National Institute for Health. Heat stroke is a form of hyperthermia. 

The family was reported missing on Aug. 17 and was found dead the following day along the Savage-Lundy Trail in Devil’s Gulch near Hites Cove, southwest of Yosemite National Park. Initial autopsy results showed no clear cause of death, leading to an ongoing investigation that baffled officials. 

Mariposa County Sheriff investigators worked with toxicologists, environmental specialists, the FBI and other experts. Previously, they had ruled out the deaths were caused by a gun or any other weapon, a lightning strike, carbon monoxide, carbon dioxide, cyanide exposure, illegal drugs, alcohol or suicide.

Since the death of the family, toxic algae had been considered as a possible cause of death, especially since the U.S Forest Service closed several hiking trails and recreational sites alongside the river and near where the family was found due to “unknown hazards.” Water samples taken nearby had shown high levels of toxic algae in the water.

However, Briese said investigators determined none of the family members had ingested any toxic algae. The family only had one water bottle, an 85-ounce container, with them, which was empty. When they were on the trail, temperatures reached up to 103 degrees Fahrenheit. 

Briese added a phone that was recovered at the scene belonged to Gerrish, and it was sent to the FBI in hopes of seeing if Gerrish attempted to call for help.

“The loss of a close relative is pain almost beyond words. When that loss is multiplied by four and one of that four is a baby of just one year old, then that pain is indescribable,” Sheriff’s spokesperson Kristie Mitchell said in a statement shared by the victims’ family.  “Some questions have been answered, and we will use this information as a way of helping us come to terms with the situation. However, the question of why can never be answered and will remain with us.

“Our hearts will never forget the beautiful lives of Jonathan, Ellen, Miju and of course Oski, as they will remain with us wherever we go,” the statement read.