Colorado - Criteria: C (architecture/engineering)
| Lookout Mountain Park |
| Loretto Heights Academy |
| Lorraine Lodge |
| Lost Lake Trail |
| Lost Trail Station |
| Loveland State Amory |
| Macedonia Baptist Church |
| Main Avenue Historic District |
| Main Street Bridge |
| Maitland Arroyo Bridge |
| Maitland Estate |
| Mancos High School |
| Mancos Opera House |
| Manhattan Hotel |
| Manitou Bathhouse |
| Manitou Springs Bridges (2) |
| Manitou Springs Historic District |
| Marble City State Bank Building |
| Marble High School |
| Marble Jailhouse |
| Marble Town Hall |
| Margery Building |
| Maroon Creek Bridge |
| Masonic Temple Building |
| Matchless Mine |
| Mathews House |
| Maxwell Building |
| Maxwell, R. G., House |
| Maysville School |
| Maytag Aircraft Building |
| McAllister House |
| McClelland Orphanage |
| McClellan House |
| McClintock Building |
| McClure House |
| McCormick House |
| McCourt, Peter, House |
| McCreery, William H., House |
| McGraw Ranch |
| McGregor Hall |
| McHugh-Andrews House |
| McIntire Ranch |
| McPhee and McGinnity Building |
| McPhee and McGinnity Paint Factory |
| Mechanics Building/Masonic Building |
| Medano Ranch Headquarters |
| Meeker I.O.O.F. Lodge-Valentine Lodge No. 47 |
| Melvin School |
| Mesa Schoolhouse |
| Mesa Verde Administrative District |
| Mesa Verde National Park |
| Methodist Episcopal Church |
| Methodist Episcopal Church of Montrose |
| Metzger Farm |
| Midland Savings Building |
| Midland Terminal Railroad Depot |
| Midland Terminal Railroad Roundhouse |
| Midway House |
| Millage Farm Rural Historic District |
| Mill City House |
| Milner Pass Road Camp Mess Hall and House |
| Miner Street Bridge |
| Minnequa Steel Works Office Building and Dispensary, Colorado Fuel and Iron Company |
| Mint Saloon |
| Miramont |
| Missouri Heights School |
| Modoc Mill |
| Monaco Street Parkway |
| Montclair Park |
| Monte Vista Downtown Historic District |
| Monte Vista Library |
| Montezuma Schoolhouse |
| Montezuma Valley Irrigation Company Flume No. 6 |
| Montezuma Valley National Bank and Store Building |
| Montgomery Court |
| Montgomery Hall, Colorado College |
| Montgomery Ward Building |
| Montoya Ranch |
| Montrose City Hall |
| Montrose County Courthouse |
| Montrose Masonic Temple, Lodge No. 63 |
| Montview Boulevard Presbyterian Church |
| Monument Lake Park Building and Hatchery Complex |
| Monument Valley Park |
| Moore, Dora, Elementary School |
| Moraine Park Museum and Amphitheater |
| Morgan County Courthouse and Jail |
| Morley Bridge |
| Mosman House |
| Mosque of the El Jebel Shrine |
| Mountainside Lodge |
| Mount Saint Scholastica Academy, East Building |
| Mount St. Gertrude Academy |
| Mount Vernon House |
| Mt. Pleasant School |
| Nachtrieb-Kelly Ranch |
| National Hotel-Wolff Building |
| Navajo Hogan |
| Neef, Frederick W., House |
| Nettleton-Mead House |
Data from United States Park Service and Wikidata
