Snowfall and blizzard conditions were expected to continue until midnight local time in parts of Colorado, the National Weather Service said, and by evening three feet (1 meter) of snow had dropped in high-altitude areas.
In Cheyenne, Wyoming, about 26 inches (65.5 cm) of snow had fallen by noon, the National Weather Service reported, setting a new two-day record for the city.
"STAY HOME. YOU WILL BE STRANDED!" the agency's Cheyenne office posted on Twitter.
The message was echoed by police agencies throughout the region, as National Guard soldiers rescued stuck motorists.
“We are responding to a bunch of stranded people in their cars throughout the county,” the Douglas County Sheriff’s Office, south of Denver, said on Twitter. “Please, please stay home. One of our deputies and a plow driver even had problems.”
All state government offices in Denver and surrounding suburban counties not essential to public safety will be closed on Monday due to the extreme weather conditions, Governor Jared Polis said in a statement.
One of the hardest hit areas was in the town of Nederland, in the foothills west of Boulder, where three feet of snow has fallen over the weekend, the weather service said.
In eastern Colorado, wind gusts of 45 miles per hour (72 km per hour) prompted the National Weather Service on Sunday afternoon to issue a blizzard warning for about a 90-mile (145 km) stretch of the state's urban corridor along Interstate 25, from Fort Collins to Castle Rock.
The warning extended to the Denver metropolitan area, where about a foot (30 cm) of snow had fallen by midday, with another 8 inches (20 cm) likely before the storm wanes by nightfall, said Frank Cooper, a National Weather Service meteorologist in Boulder, Colorado.
The deteriorating conditions forced Denver International Airport, the nation's fifth-busiest airport, to close all six of its runways, officials said. By nightfall, two feet of snow had fallen at the airport, which will remain closed until conditions improve.
The heavy, wet snow was threatening trees and power lines. During the afternoon, more than 57,000 customers were without power in Colorado, a number that dropped to about 24,000 by evening, according to an outage tracker maintained by utility Xcel Energy.
Interstates 70 and 25, Colorado's the main roadways, were shut down as of Sunday afternoon. Interstate 80, which runs east-west across Wyoming, was also closed.
The system bringing blizzards to the Rockies was also responsible for severe thunderstorms in Texas, including reports of multiple tornadoes on Saturday in the Texas Panhandle. No deaths were reported.