Investigators finally release the cause of death for a family who mysteriously died hiking near Yosemite - CNN

The cause of death for Jonathan Gerrish, Ellen Chung and their 1-year-old daughter, Miju, was hyperthermia with possible dehydration due to environmental exposure, Mariposa County Sheriff Jeremy Briese said at a news conference Thursday.

"This is a very tragic incident, tragic situation, and has been very unique from the onset," Briese said.

The cause of death for the family dog, Oski, is still undetermined, according to the sheriff, but they also suspect heat-related issues.

The hyperthermia deaths are the first Briese has seen in his 20 years in Mariposa County, he said.

Search-and-rescue workers found the family August 17 in a remote area of the Sierra National Forest near the south fork of the Merced River, according to the sheriff's office.

The trail has several steep inclines and the couple had hiked approximately 6.1 miles in temperatures ranging from the mid 70s to around 108 degrees, according to Briese.