In the late nineteenth and early twentieth centuries, there were two main methods used for underground coal mining. The first of these was known as longwall mining. The best way to understand longwall mining is to think of a coal field an enormous, widespread mass of coal. After constructing the main entry, two parallel tunnels would be drilled, several hundred feet apart. Miners would then be able to work at the broad coal face between the tunnels, allowing the roof to collapse behind them as they moved forward. Originally developed in
Europe, longwall mining was more efficient at extracting coal, though more costly due to the extra work associated with tunnel building. Various attempts to use the longwall method were made in the Roslyn field in its early stages but were abandoned due to the varied conditions of the coal seams and mine situations.
After these early experiments, all mining done in the Roslyn-Cle Elum field was done using the room-and-pillar method. In this classic mining method, main entries would be opened into the mine, stretching horizontally into the coal seam. Along the main passageway, usually at intervals of approximately 400 feet, miners would carve outside entries, creating rectangular sections of the coal seam. From these passageways, miners would open rooms of varying width directly into the coal seam. As a room was being worked, the active end was known as the coal face. Depending on the thickness of the coal seam, a coal face could be as low as two or three feet and as high as ten, fifteen, and even higher.
Miners at the coal face would leave behind pillars as they worked through a room; pillars were simply unmined sections of coal that helped support the active passageways. After all the rooms in a section, or panel, had been completed, the process of pillar removal would begin. Pillars were removed in retreat from the finished end of the section, and pillar removal left unsupported sections of the mine. the most efficient and skillful miners were in charge of pillar removal, as it was even more dangerous than normal activity at a coal face. The resulting instability and frequent collapses in the mined sections would effectively end the productive life of those sections, and mining would continue in the same fashion in another segment of the mine.