Officials in Mariposa County cannot figure out how a Northern California couple, their 1-year-old child, and their dog died while hiking, Fox News reports. The family was reported missing Monday night after John Gerrish, the husband, did not report to work. Gerrish, his wife Ellen, their daughter Miju, and their dog, were found dead along a hiking trail in Sierra National Forest. Autopsies have been completed but authorities are still dumbfounded. “There’s just still so many [potential causes of death] that we can’t rule out,” Mariposa County spokesperson Kristie Mitchell said. “We’ve looked at lighting strikes in the area. We’ve looked at storms… the weather, animals. We’re looking at the entire area as a whole.”

Officials have pondered whether a mix of carbon monoxide poisoning, toxic gasses, or algae may have contributed to the family’s death. Toxicology results are still outstanding but the bodies had no signs of physical wounds or trauma and no suicide note was left. “It makes for a very unique, very strange situation,” Mitchell said.