Accomplished Vermont environmental attorney Mark Sinclair disappeared along a hiking trail in Glacier National Park in Montana this month, and authorities haven't found signs of him more than a week after scaling back search-and-rescue efforts.

Sinclair entered the popular, mountainous Highline trail on the afternoon of July 8 after leaving his car and dog unsecured at the Logan Pass Visitor Center atop the park's famed Going-to-the-Sun Road. Search crews scanned the area by foot and air for more than a week but called off the response July 18, according to park officials.

Sinclair, 66, spent two decades advocating for environmental issues in Vermont. He directed the Conservation Law Foundation's Vermont office, worked at the Clean Energy Group and served as an attorney for the state Agency of Natural Resources and the Public Utility Commission.

He left Vermont several years ago and returned to his roots working in national parks, said longtime CLF colleague and friend Chris Kilian. Sinclair hired Kilian, now CLF-Vermont's vice president of strategic litigation, in the late 1990s. They've stayed in touch over the years and last communicated via Facebook Messenger in June, Kilian said.

"A lot of us were really feeling very positive about Mark going back to work in the park service, and he seemed very positive about it as well," Kilian said.

A Glacier National Park spokesperson told Seven Days that Sinclair had worked briefly this summer as a visitor services assistant, but his employment had ended.

Sinclair was a leader during several key environmental disputes. Kilian said Sinclair worked on the front lines for years to oppose completion of the "Circ" highway project, a victory that has been an important "bulwark against the New Jersey-fication of Chittenden County."

Clean Energy Group president Lew Milford, for whom Sinclair worked until 2013 or 2014, credited him with developing the legal theory that put Vermont Yankee on the path to closure.

 "People who feel strongly about having that plant closed have him to thank," Milford said.

While Sinclair was a gifted litigator, he turned his attention away from the courtroom during his later years in Vermont and instead sought to change how businesses made decisions, said Pat Parenteau, professor of law at Vermont Law School. Convincing businesses that environmental protection could also be a sound business strategy was "one of his signature accomplishments," Parenteau said.

Milford and Kilian said they remain hopeful that Sinclair will emerge unscathed. "Maybe we'll be surprised and Mark will show up in Mexico with a Margarita somewhere," Milford said.

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