| Macanie, John | 8-18-1919 | - | Italian | M | 0 | Oakdale | Explosion of gas due to defective lamp |
| Maes, Felix | 10-23-1926 | 30 | Mexican | M | 3 | Kebler #2 | Pinned between a car & rib |
| Magnuson, Charles | 3-4-1923 | 49 | American | M | 4 | Alamo | Run away car |
| Magon, John | 5-21-1909 | 32 | Austrian | M | 1 | Hezron | Fall of rock |
| Mahas, Gus | 3-4-1923 | 45 | Greek | M | 4 | Alamo | Run away car |
| Majestic, Mike | 1-2-1901 | 45 | Slavonian | M | - | Pryor | Fell from trip rider |
| Makoyne, Y. | 8-4-1906 | 30 | Japanese | S | - | Champion | Fall of drawslate |
| Manini, John | 11-15-1910 | 42 | Italian | M | 4 | Wooten | Fall of rock |
| Marcinko, Mike | 6-23-1914 | 38 | Austrian | M | 4 | Walsen | Struck by moving mine cars |
| Marcus, Frank | 1-20-1902 | - | - | - | - | Pictou | Explosion |
| Marquez, Miguel | 8-18-1919 | | Mexican | | | Oakdale | Explosion of gas due to defective lamp |
| Marquis, Frank | 1-20-1902 | | | | | Pictou | Explosion |
| Martery, Pete | 1-31-1911 | 19 | Italian | S | - | Midway | Fall of rock |
| Martin, James D. | 8-4-1901 | 47 | Italian | M | - | New Walsen | Fall of rock |
| Martinez, Benjamin | 10-15-1934 | 37 | American | M | 6 | Toltec | Electrocuted |
| Martinez, Daniel | 10-8-1923 | 52 | Mexican | - | 4 | Cuchara Canon | Fall of rock |
| Martinez, Edward | 4-17-1951 | - | - | - | - | Kebler #2 | Tipple mach. |
| Martinez, Fred C. | 1-3-1929 | 22 | Mexican | M | 0 | Calumet #1 | Fall of coal |
| Martinez, J.M. | 4-13-1905 | 35 | Mexican | M | - | Midway | Fall of rock |
| Martinez, Jeronino | 5-20-1924 | 39 | Mexican | M | 5 | Alamo | Fall of coal |
| Martinez, Jesus E. | 9-24-1924 | 23 | Mexican | - | - | Mutual | Fall of coal |
| Martinez, Joe E. | 4-24-1944 | - | - | - | - | Gordon | Suffocation |
| Martinez, Jose L. | 12-2-1897 | - | - | - | - | Pictou #1 | Fall of rock |
| Martinez, Joseph | 7-27-1914 | 33 | Mexican | M | 2 | Ravenwood | Run over by a loaded car |
| Martinez, Julian | 6-3-1924 | 35 | Mexican | M | 5 | Alamo | Fall of rock |
| Martinez, Liermo | 3-9-1914 | 27 | Mexican | M | 1 | Breen | Electrocuted |
| Martinez, Tony A. | 6-16-1942 | - | - | - | - | Gordon | Roof fall |
| Martis, Harris | 7-15-1918 | 32 | Greek | M | 2 | Oakdale | Fall of top coal |
| Maschic, Ben | 2-15-1910 | 29 | Austrian | S | - | Huerfano | Fall of roof |
| Mason, Matt | 1-9-1908 | 34 | German | S | - | Midway | Struck by run away car |
| Matioda, Joe | 8-6-1915 | 42 | Italian | M | 4 | Ravenwood | Fall of rock |
| Mattine, Angelo | 6-3-1905 | 29 | Italian | S | - | Midway | Fall of rock |
| Mattivi, August | 12-31-1937 | 53 | Italian | S | - | Rouse | Crushed by run away car |
| Mavor, Henry | 10-6-1910 | 41 | American | M | 2 | Robinson | Fall of drawslate |
| McCelevy | 11-7-1888 | - | - | - | - | Cameron | Fall of rock |
| McClosky, Andrew | 7-8-1922 | 40 | Lithuanian | - | - | Leader | Fall of rock |
| McCormick, J. | 7-7-1885 | - | - | - | - | Cameron | Fall of large rock |
| McCormick, John | 11-22-1884 | - | - | - | - | Walsenburg | Fall of rock |
| McCoy, Jason | 11-1-1910 | - | Scotch | - | - | Tioga | Run over by a car |
| McManamy, Mike T. | 11-20-1897 | - | - | - | - | Pictou #1 | Fall of rock |
| McNiel, Charles | 2-26-1894 | - | - | - | - | Solar | Gas explosion |
| McSparron, James | 5-22-1915 | 30 | Scotch | M | 2 | Robinson | Fall of rock |
| Medina, Mike | 2-7-1945 | - | - | - | - | Kebler #2 | Roof fall |
| Medina, Rafael | 1-2-1923 | 21 | Mexican | M | 1 | Hezron | Fall of rock |
| Melkjo, Pete | 3-13-1907 | 26 | Italian | S | - | Pinon | Fall of rock |
| Mellott, Christopher | 1-13-1930 | 43 | American | S | - | Alamo #1 | Caught between cross bar & loaded car |
| Mencin, Anton | 7-16-1923 | 32 | - | - | - | Globeville | Overcome by hydrogen sulphide gas |
| Merritt, John | 7-27-1892 | - | - | - | - | Robinson | Fall of coal |
| Metzkoviak, Adam | 8-2-1900 | 35 | Hungarian | M | 5 | Pryor | Struck by pillar |
| Micheletti, Angelo | 2-29-1932 | 54 | Italian | M | 0 | Torrid | Fall of rock |
| Micheli, James | 2-18-1913 | 35 | Italian | S | - | Larimore | Fall of rock |
| Miller, Archie | 2-19-1906 | 33 | Scotch | M | - | Maitland | Gas explosion |
| Miller, David | 10-14-1914 | 59 | Scotch | M | 7 | Larimore | Fall of rock |
| Mills, John | 11-6-1901 | 18 | - | - | - | Pictou | Fall of rock |
| Mills, Verlin | 1-7-1944 | - | - | - | - | Butte Valley | Machinery |
| Mitchell, Roy | 12-20-1932 | 40 | American | M | 2 | Calumet #1 | Gas explosion |
| Miyagi, Y. | 7-13-1916 | 38 | Japanese | M | 0 | Oakdale | Hit by a moving car |
| Molevich, Mark | 11-30-1918 | 52 | Slav | S | - | Breen | Fall of rock |
| Monson, Charles | 8-18-1919 | 41 | Swede | M | 0 | Oakdale | Explosion of gas due to defective lamp |
| Montomome, Battista | 5-18-1903 | 36 | Italian | S | - | Hezron | Fall of rock |
| Montoya, Sam | 10-15-1924 | 25 | Mexican | M | 4 | Oakdale | Thrown from a car against rib |
| Moran, James | 6-19-1925 | 43 | American | M | 2 | Gordon | Explosion of firedamp |
| Moran, William | 2-19-1906 | 22 | American | S | - | Maitland | Gas explosion |
| Morford, Ernest | 2-27-1912 | 33 | American | M | 5 | Pinon | Fall of rock |
| Morgan, Ralph | 8-23-1911 | 27 | American | S | - | Robinson | Crushed by car & rib |
| Morgueski, Joseph | 8-18-1919 | 29 | Pole | M | 0 | Oakdale | Explosion of gas due to defective lamp |
| Morich, Frank | 12-30-1909 | 27 | Hungarian | M | 2 | Midway | Fall of coal |
| Morihara, M. | 11-23-1904 | 27 | Japanese | S | - | Maitland | Fall of rock |
| Moser, Sam | 2-15-1910 | 21 | Austrian | S | - | Huerfano | Fall of roof |
| Moyer, Harvey | 6-19-1925 | 39 | American | M | 3 | Gordon | Explosion of firedamp |
| Mrah, Vincent | 10-14-1912 | 50 | Austrian | M | 1 | Chandler | Fall of rock |
| Muir, David E. | 9-28-1892 | - | - | - | - | Walsen | Explosion of gas |
| Muir, Grover C. | 2-6-1928 | 22 | American | S | - | Pictou | Fell off trip |
| Mullitz, John | 10-1892 | | | | | Rouse | Fall of rock |
| Muneck, Mike | 9-5-1900 | 23 | Slav | S | - | Toltec | Fall of rock |
| Murray, Richard D. | 8-30-1915 | 35 | Scotch | S | - | Toltec | Electrocuted |
| Music, Mike | 8-20-1918 | 44 | Austrian | S | - | Sunnyside | Fall of rock |
| Muyata, H. | 5-5-1920 | 40 | Japanese | M | 1 | Sunnyside | Fall of rock |
| Muzzies, M. | 8-18-1919 | 33 | Mexican | S | - | Oakdale | Explosion of gas due to defective lamp |
| Nagy, Steve | 6-10-1925 | 37 | Hungarian | M | 4 | Cameron | Fall of rock |
| Nakashima, Sakajiro | 12-30-1915 | 33 | Japanese | M | - | Oakdale | Fall of top coal |
| Nakatani, K. | 3-13-1905 | 35 | Japanese | M | - | Walsen | Fall of roof |
| Naranjo, Manuel | 9-3-1904 | 60 | Mexican | M | - | Midway | Fall of rock |
| Negro, Dominic | 1-16-1944 | - | - | - | - | Kebler #2 | Face bimp |
| Nelson, Mose | 5-19-1930 | 35 | American | M | 2 | Calumet #2 | Crushed between car & rib |
| Nikola, Nik | 4-26-1917 | - | Bulgarian | M | - | Tioga | Fall of rock |
| Nilas, Rudolph | 10-31-1914 | 32 | Hungarian | S | - | Oakdale | Fall of rock |
| Nizzi, F. | 2-19-1906 | 35 | Italian | S | - | Maitland | Gas Explosion |
| Nizzi, J. | 2-19-1906 | 28 | Italian | S | - | Maitland | Gas explosion |
| Nogic, V. | 1-21-1904 | 30 | Italian | S | - | Rouse | Hit by runaway mine cars |
| Norare, Eleseo D. | 8-11-1923 | 22 | Italian | S | - | Rugby | Fall of rock |
| Norvasd, John | 6-17-1917 | 36 | Pole | M | 3 | Cameron | Fall of rock |
| Notman, Walter | 4-24-1907 | 24 | Pole | M | - | Midway | Gas explosion |
| O'Brien, James | 12-12-1888 | - | - | - | - | Rouse | Run over by pit car |
| Odderzzi, Joseph | 7-23-1906 | 42 | Austrian | M | - | Rouse | Fall of rock |
| Olds, Robert E. | 9-30-1907 | 59 | American | M | - | Huerfano | Struck by cage on top of shaft |
| Omelenchuk, Alex | 1-30-1925 | 32 | Russia | S | - | Robinson #2 | Fall of rock |
| Ortez, Jake | 10-28-1920 | 30 | Spaniard | M | 1 | Sunnyside | Crushed between mine car & pillar |
| Owens, David | 10-10-1898 | 40 | Welsh | M | - | Pictou | Fall of rock (family in Wales) |
| Owens, Walter M. | 3-7-1927 | 39 | American | M | 3 | Robinson #2 | Fall of drawslate |
| Oxford, Alfred | 8-18-1919 | 17 | American | S | - | Oakdale | Explosion of gas due to defective lamp |