The parents, John Gerrish and Ellen Chunt, went hiking early on the morning of Aug. 15 with their 1-year-old daughter, Miju, and their dog, Oski, in the Sierra National Forest.
The next day, a Monday, Gerrish didn't show up to his job as a software engineer, so a friend reported the family missing later that night.
Their car was located near the Savage Lundy Trail about two hours after midnight on Aug. 17, and their bodies were found hours later around 9 a.m. about 1.5 miles down the trail.
Autopsies performed on Thursday did not turn up many clues, but authorities are still awaiting toxicology reports on the family and their dog.
Investigators are now hoping that a cellphone found on the family may turn up evidence of what killed them. Police delivered that phone to the FBI for data extraction on Tuesday, which they are still waiting on results for. A search warrant was also issued on Wednesday for possible social media access.
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The family was found with no obvious signs of trauma, leading investigators to rule out gunshots and chemical hazards in their deaths. Kristie Mitchell, a spokeswoman for the Mariposa County Sheriff, said they have also ruled out homicide.
"Initially, yes, when we come across a family with no apparent cause of death, there's no smoking gun, there's no suicide note, there's nothing like that, we have to consider all options," Mitchell previously told Fox News on Saturday. "Now that we're five days in, no, we're no longer considering homicide as a cause of death."
Investigators are looking into a range of other possible causes, including toxic algae and abandoned gold mines that can produce toxic gases.
The California Department of Fish and Wildlife warned last month that the water along the Merced River near Hites Cove had "a high concentration of algae bloom," which can contain toxins that are poisonous to humans and pets.
The area in central California is home to abandoned gold mines from the mid-19th century, which are known to produce toxic gases, but Mariposa County Sheriff Jeremy Briese told the Fresno Bee last week that he doesn't think the mines played a role.
The sheriff's office also noted Thursday that temperatures were extremely high during the day on Aug. 15, ranging from 103 to 109 degrees.
"We know the family and friends of John and Ellen are desperate for answers, our team of detectives are working round the clock," Sheriff Briese said in a statement Thursday. "Cases like this require us to be methodical and thorough while also reaching out to every resource we can find to help us bring those answers to them as quickly as we can."