The cause of death of a Northern California family after their hike in August was revealed by the Mariposa County Sheriff’s Office.

Hyperthermia and “probable” dehydration were believed to have killed 45-year-old Jonathan Gerrish, his wife, 30-year-old Ellen Chung, and their daughter, Miju, Mariposa County Sheriff Jeremy Briese told a media briefing on Thursday.

“Heat-related deaths are extremely difficult to investigate, and we want to thank you all for being patient with us,” Briese said.

According to the investigation done by the sheriff’s office and the more than 30 agencies, the family took miles of trails on their hike and eventually led to their passing.

Last Aug. 15, a witness said they saw the family on the Hites Cove Trail as they walked to a 2.2-mile stretch to the U.S. Forest Service trail lying parallel to Merced River’s south fork. The location is elevated by 1, 930 feet. Then, they headed to the Savage Lundry Trail, which took them 1.9 miles of walking. The family reached a steep slope, and without any shade and the high elevations, temperatures there hit 107 to 109 degrees. According to the sheriff, the temperature was in the 70s when the family started hiking. Hyperthermia triggered by 105 degrees of temperature can lead to damage to the brain and organs. It can become the cause of deadly heatstroke.

The family only had an 85-ounce water bladder when they were found dead on Aug. 17. Their location was not near a water source, like containers or filtration systems.

The sheriff, however, did not specify what caused the death of the family’s dog, Oski.

The drone footage was presented by Briese during the news conference. It showed the path the young family took before their bodies were recovered.

In addition, Briese said there is no proof that the family consumed any water that contains toxic algae, despite that algal blooms were confirmed through a test on the water from many locations along the Merced River, SFGATE reported.

The revelation concluded the investigation on the case which took about three months.