Some of the greatest totals from the snowstorm were in Wyoming, where up to 17 inches of snow fell in Natrona County.
The storm system brought snow to Yellowstone National Park on Monday, with videos showing snow falling on a bison on Monday.
"Surely this bison is a metaphor for something in 2020," Chris Frink wrote on Twitter.
Yellowstone closed the park’s east entrance on Monday due to winter weather conditions. “At this point, there is no reopening date and time available,” the Big Horn Radio Network said.
In Montana, where the weather began to shift Sunday night, the small city of Red Lodge, a gateway to Yellowstone National Park, had received 10.5 inches of snow.
Farther north in Glacier National Park, snow closed the higher elevations of the Going-to-the-Sun Road. Jackson Hole in Wyoming was also greeted with fresh snow.
The abrupt end of summer in Denver came on Tuesday, as temperatures dropped and snow fell throughout the metro area.
A winter weather advisory was issued for the Denver, Boulder, and Fort Collins areas through 12 pm Wednesday, with two to six inches of snow forecast.
Many took to social media to show the September snowfall in the city, including the Colorado Rockies.
Six inches or more of snow could fall in the northern and central Rockies, with 1 to 2 feet dropping in the highest peaks, according to the NWS. It has issued scattered winter storm warnings and weather advisories from southern Montana to southern Colorado.
Freeze and frost warnings also were posted for parts of Montana, Idaho, Colorado, Nebraska, North Dakota, and Minnesota.
The cold and snow are expected to help the fight against the Cameron Peak Fire in northern Colorado, which nearly quadrupled in size over the weekend, sending smoke and ash into Denver.
The wild weather system also impacted nearby Utah, where temperatures plummeted by 40 degrees and wind gusts of nearly 100 mph roared through Salt Lake City, downing trees and canceling the first day of online school.
The same storm will continue to spread snow into parts of the High Plains through Thursday and then things will taper off and temperatures will normalize.
The cold air mass that brought the snow along with it is going to help cool off the temperatures for the interior West. However, the coast is still dealing with critical fire danger on Wednesday as strong winds from the winter storm over the Rockies perpetuate an already dire situation.
Winds will calm down a bit by Thursday, but there’s no major relief in the forecast for this area in the short term.
Cooler temperatures are the story for much of the Plains on Wednesday.
Along the cold front, heavy rain and thunderstorms will be possible with the risk of flash flooding for parts of Texas, Oklahoma and Kansas.
The Associated Press contributed to this report.