RAPID CITY, S.D. -

Authorities say a prairie fire that burned 48 square miles in western South Dakota was human-caused.
    
The Cottonwood Fire began Sunday afternoon east of Rapid City, in the Wall and Cottonwood areas. It scorched private land and part of the Buffalo Gap National Grassland. Firefighters were mopping up Monday and investigating the damage.
    
The fire burned numerous rural buildings, though no homes. It produced smoke that cut visibility on Interstate 90 and contributed to at least two crashes. It also destroyed power poles, cutting electricity to some rural areas, and killed dozens of livestock. There were no reports of any people injured.
    
About 300 firefighters from 10 western counties fought the blaze at its peak. The state fire marshal's office is continuing to investigate the cause.