As owner of the Diamond Cross Ranch, an 82,000-acre (33,000 ha) parcel along Montana’s Tongue River and on the northern end of the Powder River Basin, Mars was active in opposing the development of his part of what's been called the "most productive coal and natural gas fields in the nation." Companies that hold the oil and gas leases to his land, rights originally made possible by the Stock-Raising Homestead Act and the Mineral Leasing Act, are seeking to exercise those rights on his ranch. Mars was reportedly concerned about the large amount of water that Energy exploration and production projects consume, water needed by his ranch.