WHITEFISH, Mont. — As a child in this town at the edge of the Continental Divide, Ryan Zinke cut his own trails through alpine forest, swam laps in Whitefish Lake and hiked the snow-packed paths of nearby Glacier National Park.

Later, as an Eagle Scout, he traced how railroad oil spilled into the Whitefish River and watched as a single spark set that waterway on fire. “The project,” he wrote in his 2016 book, “promoted a lifetime of conservation values.”

President Trump has tapped Mr. Zinke, 55, a House member and fifth-generation Montanan who grew up in this timber-and-tourism community, to be secretary of the interior. He was confirmed by the Senate on Wednesday by a vote of 68 to 31.

The position puts Mr. Zinke in control of 500 million acres of United States land — roughly a fifth of the nation — and charged with balancing the department’s contradictory duties of conserving land and mining it for resources at a time of intense pressure from energy producers, environmental activists, state lawmakers and his own boss, who made fossil fuel jobs a crucial part of his campaign platform.