Montana Governor Steve Bullock declared an emergency on Sunday as a snowstorm dumped record amounts of wind-driven snow that caused hazardous travel conditions and scattered power outages.
Winter storm warnings were posted for parts of western Montana, northern Idaho and north-east Washington.
Snow also was forecast for areas in Wyoming, Utah, Oregon, Nevada and California.
The brunt of the storm hit Montana where up to 2 feet (61 centimetres) of snow fell on Saturday in the mountains and a record 14 inches (35.5 centimetres) fell in Great Falls with snow still falling on Sunday.
“With an unprecedented winter storm throwing our state a surprise in September, state and local governments are working closely together to protect the health and safety of Montanans and our top priority is making sure that happens,” Mr Bullock said in a statement.
“Montanans should heed all warnings from state and local officials, travel safely, and be cautious during this time.”
Major interstates and highways remained open, but snow and ice covered many stretches of roadway in western Montana.
The storm was expected to wind down late on Sunday and early on Monday.