SAN FRANCISCO — The remote forest area where the bodies of a California couple, their baby and the family dog were found was being treated as a hazmat site as authorities look for any clues on what caused the mysterious deaths.

Investigators were considering whether a toxic substance, such as gas from mines in the area or algae, could have been responsible, said Kristie Mitchell, a spokesperson for the Mariposa County Sheriff’s Office.

“This is a very unusual, unique situation,” Mitchell told the San Francisco Chronicle. “There were no signs of trauma, no obvious cause of death. There was no suicide note.”

John Gerrish, his wife, Ellen Chung, their 1-year-old daughter, Muji, and their dog were all found dead Tuesday on a hiking trail near Hite’s Cove in the Sierra National Forest. A family friend had reported them missing Monday evening.

The area around Hite’s Cove was the site of a hard rock gold mining operation in the mid-19th century, the Chronicle reported.

The bodies were transported to the coroner’s office in Mariposa for autopsies and toxicology exams, Mitchell said.

The couple were known to be avid hikers. Their friend, Mariposa real estate agent Sidney Radanovich, said Gerrish was a San Francisco-based software designer who, with his wife, “fell in love with the Mariposa area” and bought several homes there, a residence and rental investments.

“They were such a loving couple, they loved each other quite a bit,” Radanovich told the newspaper. “He loved showing the baby all sorts of things and explaining them to her.”

The sheriff’s office was investigating the deaths along with the California Department of Justice.

Sheriff Jeremy Briese said chaplains and staff were counseling family members.

“My heart breaks for their family,” he said.

The remote area where the bodies were found had no cellphone service, Mitchell said. The hiking trail ran through an area of forest known particularly in springtime to have spectacular wildflower displays.