Union Pacific Corp. will combine two subsidiaries.

Champlin Petroleum and Rocky Mountain Energy will be merged into a single operating company called Union Pacific Resources, according to Union Pacific Chairman and Chief Executive William A. Cook. Headquarters for the new subsidiary will be in Fort Worth. Cook said the change will enable UP to make further cost and productivity improvements in the natural resource businesses and to manage them more effectively. UP bought Champlin, the firm’s oil and gas company based in Fort Worth, in 1970. Rocky Mountain, based in Denver, is the company’s coal mining branch created in 1971. Cook said that work force reductions will be made as a result of the consolidation, with up to 100 positions affected.