A beloved Palo Alto dentist has gone missing in the Wyoming wilderness after he became separated from his hiking group over the weekend, the Fremont County Sheriff's Office and his niece said.

Steve Keller, 76, was reported missing on Saturday, Sept. 2 at around 4:30 p.m. in the Wind River mountains near Lander, Wyoming, the Fremont County Sheriff's Office said in a press release on Sept. 5.

Keller was hiking near Steamboat Lake in a remote area of the Wind River Reservation. Keller left Steamboat Lake, where his group was camping, for a day hike without a pack, according to a police missing persons flier.

Search and rescue teams, including helicopters, are looking for Keller but weather conditions have caused delays.

“Weather conditions have severely impacted the search effort as thunderstorms have moved through the area and limited the ability to conduct air operations at times,” the Fremont County Sheriff's Office said.

"We are deeply concerned," Keller's niece, Betsy Briggs Miller, said in a Facebook post, asking the public to share the information if they know anyone in or near the Wind River or Lander area.

She told the Cowboy State Daily that Keller is an expert outdoorsman and "very tough" with no health issues. He has taken the backpacking trip in the area many times.

"Steve is a skilled outdoorsman who has backpacked this area of the Wind River Range dozens of times. The area he went missing near Steamboat Lake is densely forested and can be disorienting," she said in a Facebook post on Tuesday.

Keller, who is retired, worked with the Palo Alto Dental Group starting in 1979. He attended Georgetown University School of Dentistry on a scholarship from the United States Navy and served as a naval officer and general dentist at Naval Air Station Moffett Field in Mountain View for three years, according to the dental group's website. He became a full partner in 1982.

"He is proficient in all aspects of general dentistry, and seeks simple solutions to complex problems. He values his relationships with patients, and always schedules enough time to explain procedures and provide thorough treatment," his website bio stated.

Keller is described as a white male who was wearing a green jacket, a black, blue and green Patagonia fleece and is 6 feet tall and weighs 170 pounds.

This story will be updated as more information becomes available.