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Authorities have confirmed that a Washington man whose body was recovered from the shore of a remote lake in Yellowstone National Park earlier in September died from exposure.

An autopsy determined that 67-year-old Mark O’Neill of Chimacum, Washington, died from hypothermia, park officials revealed Wednesday. Search and rescue crews found O’Neill’s body along the eastern shore of Shoshone Lake on Sept. 20.

The remote lake in the southwestern corner of the national park is Yellowstone’s second-largest.

O’Neill was a retired National Park Service employee, according to the park. Officials did not elaborate on O’Neill’s career.

The search for O’Neill’s brother, 74-year-old Kim Crumbo of Ogden, Utah, has continued since the two men were first reported missing.

Crumbo is a Vietnam veteran, a former Navy SEAL, a wilderness and wildlife advocate and a retired Grand Canyon river ranger for the National Park Service.

On Wednesday, crews from Yellowstone National Park continued to search for Crumbo by foot and boat. Grand Teton National Park’s interagency helicopter and dog teams from Western Montana Search Dogs were helping them.

Crews from the National Park Service’s Submerged Resources Center on Wednesday were still using sonar equipment to look for clues in the waters of Shoshone Lake, according to park officials.

The recovery efforts will continue in the upcoming days as conditions warrant, park officials wrote in a Wednesday update.

The average year-round temperature of Shoshone Lake is about 48 degrees, according to the park. At that temperature, experts estimate that people can survive in the water for between 20 and 30 minutes.

Crews have been looking for Crumbo on and near Shoshone Lake. They’ve scoured all area trails. Their rescue efforts switched to recovery efforts on Sept. 24.

A family member first reported that O’Neill and his brother were overdue from a four-night backcountry trip to Shoshone Lake on Sept. 19, according to officials.

After Crumbo and O’Neill were reported overdue, search and rescue teams found a vacant campsite and gear on the south side of the lake. They also found a paddle, canoe, a personal floatation device and other belongings on the lake’s eastern shore.

Park staff are encouraging people with any information that could help investigators to contact 307-344-2428 or

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Helena Dore can be reached at or at 582-2628.

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