MARIPOSA, Calif. (KSEE/KGPE) — Officials from the Mariposa County Sheriff’s Office revealed the cause of death Thursday in what killed an entire Mariposa family and their family dog on a hiking trail in the Sierra National Forest.

According to Mariposa County Sheriff’s Department officials, the cause of death for Jonathan Gerrish, Ellen Chung and Aurelia Miju Chung has been determined to be “hyperthermia and probably dehydration due to environmental exposure.” The cause of death for Oski, the family dog, is as of yet undetermined, although officials add that the dog was possibly suffering from heat-related issues.

Officials say the trail the family was hiking on was exposed to constant sunlight with very little shade, with temperatures between 107° and 109°.

Jonathan Gerrish, 45; Ellen Chung, 30; Aurelia Miju Chung, 1; and their family dog Oski were found dead Aug. 17 on the Savage Lundy Trail in Mariposa County. Since then, investigators have ruled out several causes of death, including a gun or any other type of weapon, chemical hazards along the Savage Lundy trail, lightning strike, carbon monoxide, carbon dioxide, cyanide exposure, illegal drugs or alcohol or suicide.

Much speculation has centered around the possibility that toxic algae contributed to the family’s death after Mariposa County Sheriff Jeremy Briese said toxic algae is “known to be present” in the water of the South Fork of the Merced River. Officials have said that they are looking at all possible causes for their death including signs of toxic algae.

According to officials from the sheriff’s office, multiple water samples were taken in the area close to where the family was found, and of the water in their flasks. Those samples were sent to the State Water Board for testing.

However, in a statement Aug. 24, the State Water Board released a statement regarding their death.

“Representatives from the Central Valley Water Board, the county health department, and the sheriff’s department collected water samples from multiple sites along the Merced River on Thursday to test for the presence of HABs. The State Water Board expects to have findings from these tests within two weeks. It is important to note that lethal impacts to humans from cyanotoxins or cyanobacteria found in freshwater HABs are extremely rare.”

In a news release, the sheriff’s office says the remote area where the bodies were found had no cellphone service. Additionally, the FBI is trying to access Gerrish’s cellphone, which was found in his pocket.

The Sierra National Forest has closed down several trails located in and around the Savage Lundy Trail, where the family was found. That closure is in effect through Oct. 29. According to the order,  the closure is meant to “provide for public safety due to unknown hazards found in and near the Savage Lundy Trail.”