Contact National & State Register Staff Use this map to determine which National Register historian to contact regarding your property. For the following counties contact Jason O'Brien at jason.obrien@state.co.us: For the following counties contact Jason O'Brien at jason.obrien@state.co.us: Alamosa Arapahoe Archuleta Chaffee Conejos Costilla Custer Delta Denver Dolores Douglas Elbert El Paso Fremont Gunnison Hinsdale Huerfano La Plata Lake Mesa Mineral Montezuma Montrose Ouray Park Pitkin Pueblo Rio Grande Saguache San Juan San Miguel Teller Adams Baca Bent Boulder Broomfield Cheyenne Clear Creek Crowley Denver Eagle Garfield Gilpin Grand Jackson Jefferson Kiowa Kit Carson Larimer Las Animas Lincoln Logan Moffat Morgan Otero Phillips Prowers Rio Blanco Rio Grande Routt Sedgwick Summit Washington Weld Yuma