Surface mining is used when the coal is typically less than 200 feet below the surface. Heavy equipment is used to remove the top layers of soil and rock to expose the coal. The coal is excavated, and after the mining is complete, the soil and rock are returned to reclaim the coal mining property. Then the property can be used for other purposes, such as cropland, wildlife habitat, recreation, commercial, or industrial purposes. This method is used most frequently in the United States because much of the coal reserves are near the surface and it is less expensive than underground mining. Surface mines accounted for 31 percent of statewide production. Whereas drift, contour, and auger mining are more common in eastern Kentucky, slope and shaft mining are more common in the western Kentucky coal field. Nearly 60 percent of active coal mines in eastern Kentucky in 2015 were broadly defined as surface operations. However, the combined annual production of eastern Kentucky surface mines was slightly lower than underground production: 13.5 million tons compared to 14.6 million tons.