BIRNEY — Driving along a gravel road that parallels the Tongue River, Art Hayes gestures to land once belonging to Brown Cattle Company, the ranch his great-grandfather founded when this area appeared on maps as “Montana Territory.” Hayes describes how his grandfather, “one of the last open-range cowboys,” would start trailing cattle into the Big Horn mountains in May and hope to return to Birney by Thanksgiving. The Tongue River, cottonwood-li…