President-elect Donald Trump has chosen first-term Republican Montana Rep. Ryan Zinke, a former U.S. Navy SEAL commander, as his interior secretary, a senior transition official said on Tuesday.

Zinke, 55, will be nominated to head the Interior Department, which employs more than 70,000 people and oversees more than 20 percent of federal land, including national parks like Yellowstone and Yosemite.

Zinke's choice was something of a surprise, since some Republican officials wanted him to challenge Democratic Sen. Jon Tester in the 2018 elections.