In 1864, the Des Moines Coal Company was organized to begin the first systematic mining in the region. Its first mine, north of town on the river's west side, was exhausted by 1873. The Black Diamond mine, near the south end of the West Seventh Street Bridge, sank a mine shaft to reach a coal bed. By 1876, this mine employed 150 men and shipped 20 carloads of coal per day. By 1885, numerous mine shafts were within the city limits, and mining began to spread into the surrounding countryside. By 1893, 23 mines were in the region. By 1908, Des Moines' coal resources were largely exhausted. In 1912, Des Moines still had eight locals of the United Mine Workers union, representing 1,410 miners. This was about 1.7% of the city's population in 1910.