The Boulder-Weld (originally the Northern Field) coal field covers a large area northwest to north-northeast of Denver. Colorado's first coal mine began there in 1859 near Marshall, a small town near Boulder, as a wagon mine. From 1864 (when State mining records began) to the closing of the last operational mine in 1978, there were 223 coal mines in the district. The total amount of coal mined from the coal field was approximately 111,360,372 short-tons, which is the largest amount of coal mined from Front Range coal fields. Coal was mined in a north-easterly direction, beginning mostly around Marshall and headed toward Frederick, mining successively deeper as it went. A revolutionary piece of machinery, the automated continuous miner, was invented at the Baum Mine in 1943.
Below: Map of Boulder / Weld County Coal Field Historic Mines. Orange line represents the edge of the coal region. Green dots represent the top 10 producing coal mines. Small black dots represent other historic coal mines.
Over the course of the years that the Boulder-Weld coal field was active, several large labor conflicts broke out which became known as the "Erie Wars". The most infamous of these labor conflicts began in the Northern coal field in 1913, and ended in 1914 after culminating in the Ludlow Massacre in the Southern coal field near Trinidad. Many families were killed by fire in a coal mine camp of striking miners. Shortly after the Ludlow Massacre, troops from the Colorado militia were called in to settle things down, and over the next few years conflicts resulted in hundreds dead. United States Army troops took control of the violence and along with other help from people like Boulder County sheriff Stanford Buster, things quieted down through the rest of 1914. The last of the major labor conflicts was in 1927, which resulted in the shooting deaths of 6 miners and an estimated 60 or more wounded at the Columbine Mine near Lafayette.
A prominent figure of the Boulder-Weld coal field was Mary Miller. In 1862, Mary and Lafayette Miller arrived in the area near the St. Vrain River and operated a stage station along the Denver-Cheyenne Road (present day US-287). They owned Rock Creek Stage Station until 1870, when the railroad to Denver was built. They homestead land for farming near present-day Lafayette. The land was successful for farming, but after Lafayette's untimely death in 1878 (of heat stroke), Mary carried on with an interest in coal mining. By 1884 coal (14 ft thick) was discovered on her farm. In 1887, coal mining began there (Simpson Mine), and in 1888 she platted 150 acres of her farm for a new town built around the coal mine and named for her late husband Lafayette. The Simpson Mine was the largest mine in northern Colorado , producing 4.126 million short-tons of coal from 1889-1927. Mary Miller was also the only female president of a bank in the world in 1900. The Lafayette Library has a mural of the Millers on the south side of the building.
Another prominent female figure to emerge from the Boulder-Weld coal field was Josephine Roche. Roche inhereted the Rocky Mountain Fuel Company holdings of her father in 1927. By 1929 she had purchased a majority interest in the company and became president. She enacted pro-labor policies including the UMWA to return to Colorado and unionize the Rocky Mountain Fuel mines. She paid coal miners $7 per day, the highest wages in Colorado's coal mines. Rocky Mountain mines became the highest productivity mines in Colorado in the 1930s. President Roosevelt appointed her Assistant Secretary of the Treasury until 1937. She returned to Colorado and Rocky Mountain Fuel, but due to economic hardships, and increased popularity of natural gas, declared it bankrupt in 1944. An open space park over abandoned coal mines in Lafayette is named after her.
Modern residential development of the area makes it unlikely for coal mining to continue in the near future. Past mines have created mine subsidence hazards on the surface today. Many buildings have been severely damaged by sinking into unknown void spaces created by abandoned mine tunnels and shafts. Documentation of mine shaft and tunnel locations aren't always complete or may have been non-existent.
Below: Coal Mine Subsidence at Cherry Vale Rd and Marshall Rd in Marshall, CO. Note the parallel horizontal rows of the old mine tunnels near the center of the image.