The Northwest Improvement Company opened the first mines in the Roslyn-Cle Elum coalfield, the Nos. 1 and 2, in August 1886, north of present-day Ronald. The company eventually opened ten different mines between 1886 and 1944, and closed the last mine in the area, the No. 9, in 1963. Over that time, it would become the largest producer of coal in Washington, and one of the primary property owners in the Roslyn area. In addition to the Northwest Improvement Company, other coal producers included the Roslyn-Cascade Coal Company, and the Roslyn Fuel Company, as well as numerous small private owners. During the coal era, over 64 million tons of coal was produced from the Roslyn-Cle Elum field. Peak production occurred in 1920 when nearly 2 million tons of coal was extracted. This followed a string of highly productive years for coal production in the upper Yakima watershed. Despite the opening of the No. 9 mine in 1928, and the introduction of machines into the mining process, total area production fell below 1 million tons by 1930. By that time, only four of the Northwest Improvement Company mines were still operational. Despite a small upsurge in production during World War II, by the mid-1940s total annual production fell below 1898 levels. The last commercial mine in the area, the No. 9, closed in 1963, but most experts estimate that the remaining reserves of coal in the Roslyn-Cle Elum field range from 170 to 270 million tons of coal.
The majority of the coal extracted from the Roslyn-Cle Elum field was used for transportation. The first coal shipments were used by the railroads to supply their locomotives. Coal from the eastern Cascades was also used for steamships, which even after the arrival of the railroads remained a major source of transport and trade in the United States.
Until the first third of the twentieth century, steam power was also indispensable to the United States Navy, and coal from the Roslyn area was used in the Spanish-American War as well as World War I. This meant that coal from Washington supplied steamships throughout the islands of the Pacific Ocean, including Hawaii and the Philippines. In addition to its use for ships, Roslyn coal was used for domestic energy. The coal beds of Kittitas County supplied to home and commercial heat for much of the West Coast, from Seattle to Portland and as far south as the burgeoning metropolis of San Francisco.
However, changes in the nature of fuel resources would eventually catch up with the coal industry. The emergence of another fossil fuel, oil, led to dramatic reductions in the amount of coal mined in the Roslyn-Cle Elum field, as well as the number of miners who brought it to light. By the mid-1920s, numerous mines in the area closed in response to decreased demand for coal and coal-based energy, and the development of cheaper coal reserves in other Western states, coupled with the development of hydroelectric power in the Northwest, eventually closed the Washington coal fields.