Because of “unknown hazards” in the area where a family and their dog were mysteriously found dead last month, federal forest officials closed trails and campgrounds in a remote area near Yosemite National Park.

According to the Mariposa County Sheriff’s Office, the bodies of Jonathan Gerrish, Ellen Chung, their 1-year-old daughter, Miju, and the family dog, Oksi, were discovered by search and rescue workers on August 17 in a remote area of the Sierra National Forest near the south fork of the Merced River. They were discovered along the Savage Lundy Trail. According to the Sierra National Forest, the area where the family was discovered was closed as a precaution due to “unknown hazards found in and around the Savage Lundy Trail.”

“All designated recreation sites, roads, and trails adjacent to and/or leading to this location will be closed to the public,” the national forest said in a statement Saturday. The closures will be in effect until September 26.

The US Forest Service has temporarily closed all national forests in California due to multiple wildfires burning in the state since the closure was announced.

The cause of the mysterious deaths has yet to be determined by investigators. Autopsies on the family members and a necropsy on the dog were both inconclusive, and toxicology results are still pending. Some results could be available as early as Wednesday, according to Kristie Mitchell, a sheriff’s office spokesperson.

The only potential causes of death that have been ruled out are gunshots or other types of weapons, as well as chemical hazards along the Savage Lundy Trail. Toxins in areas near the trail have not been ruled out by detectives.

Since mid-July, signs warning of a toxic algae bloom have been posted along the south fork of the Merced River, near where the family was discovered. Water samples from the area, as well as samples of the drinking water the family packed, were sent to labs for analysis.

The family’s home and cars were searched, but no significant evidence was found. The FBI has collected their phones and is extracting data from them.

“We know John and Ellen’s family and friends are desperate for answers, and our team of Detectives is working around the clock,” Mariposa County Sheriff Jeremy Briese said in a statement. “In cases like this, we need to be methodical and thorough while also reaching out to every resource we can find to help us get those answers to them as soon as possible.” Steve Jeffe said he met the couple years ago in San Francisco and that they became very close after they both moved to the Mariposa area.

“They were incredible people, very generous,” Jeffe said. “They are very attached to their daughter.”

According to Jeffe, who was alerted by friends after the family failed to return home from a day hike last month, Gerrish worked for Google and had recently started a job at Snapchat.

When the family’s nanny arrived the following Monday morning, she found no one home, and when Gerrish failed to show up for work, “alarm bells went off,” Jeffe said.

“They were an amazingly loving and doting family,” Jeffe said, describing the couple as well-liked by a large circle of friends. “It’s a perplexing occurrence. There’s something unsettling about what happened “Jeffe stated. “Whether it was environmental or man-made, it was clearly something they encountered,” Jeffe added, speculating on what may have caused their deaths.

Mitchell stated that the area where the family was discovered is popular in the spring because of its colorful wildflower blooms, but it is also very hot at this time of year, with little shade.

She claimed that the family was well-prepared for a day hike.