Air quality varies considerably in the vicinity of Scotts Bluff National Monument. Wind-borne particulate matter is one of the reasons for reduced air quality in the area. Because of the region's relatively low precipitation and the disturbance of the region's highly erodible soil from cultivation and other farm activities, there is frequently a considerable amount of particulate matter in the air. This is especially common in the fall during harvest, in winter when the region's fields of mostly sugar beets, corn and beans have no residual cover, and in the spring during field preparation and seeding. The light, sandy loam soil blows easily in the wind. Occasionally, during periods of extremely intense winds, Scotts Bluff is not visible from the city of Gering, only two miles away. Air quality improves considerably north and south of the North Platte River Valley. These areas are mostly native prairie and grazed by cattle. The roots of native prairie plants hold the soil and keep it from blowing. Sugar beet refineries in the North Platte River Valley contribute a considerable amount of sulfur dioxide, organic compounds, and particulate matter to the local atmosphere, but these emissions are within acceptable limits as defined by the Clean Air Act (42 USC 7401 et seq.). The haze and odor from the processing and refinement of sugar beets detracts from the visitors' experience and, at times, interferes with their ability to enjoy the scenic views of and from the Monument's summit.