Authorities in Mariposa County, California, are trying to determine why a family of three and their dog died on a remote hiking trail in the Sierra National Forest near Yosemite National Park.

Search and rescue workers found the bodies of John Gerrish, Ellen Chung, their one-year-old daughter, Miju, and the family dog on Tuesday near the Devil's Gulch area in the Southfork of the Merced River drainage, the Mariposa County Sheriff's Office said in a news release.

They had been reported missing on Monday night.

There were no immediate signs of trauma to the family members, no suicide notes, or any other clear indications of what caused their deaths, Mariposa County Sheriff public information officer Kristie Mitchell told CNN.

First responders initially treated the area as a possible hazmat scene because of concerns that carbon monoxide from nearby mines could have poisoned the family.

Last month, the US Forest Service warned that toxic algae had been discovered in the Merced River and urged people not to swim, wade or allow their pets to drink the water.

The bodies have been recovered and are being autopsied, but Mitchell said they will likely have to wait for toxicology results -- which could take weeks -- to determine the cause of death.

"This is just a tragic, frustrating case for us," said Mitchell. "It will probably be a long, tedious investigation."

The family's bodies were found on the Savage-Lundy Trail, which is popular in the spring because of its colorful wildflower blooms. Mitchell said it is very hot at this time of year and there is little shade.

She said the family was well prepared for a day hike.

There is no cell service in the area, so search and rescue crews had to rely on satellite phones for communication.

"This is never the outcome we want or the news we want to deliver, my heart breaks for their family. Our Sheriff's Chaplains and staff are working with their family and will continue to support them during this heartbreaking time," said Sheriff Jeremy Briese in a statement.

(Courtesy, CNN: Text, excluding headline)

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