'Once-In-A-Generation' Snowfall In California Leaves Roads Blocked, Traps Residents. IN PICS

The west coast of United States received unprecedented levels of snowfall with mountainous regions of California recording over 40ft of snow since the onset of winter.

Snow covered trees line the top of a mountain as seen from California State Route 18

The west coast of the United States, from Oregon to the mountains of California and Phoenix, received unprecedented levels of snowfall this week in what officials are calling a “once-in-a-generation” event. The mountainous regions of California have received over 40ft of snow since the start of the season. (Image: Getty Images)

Portland, Oregon’s largest city, saw its second snowiest day in history with almost a foot of snow, while further south in Arizona the suburbs received a dusting of snow. (Image: Getty Images)

Several towns have shut down as they are virtually cut off from the rest of the state. The governor has declared a state of emergency in 13 counties due to the unusual snowfall. (Image: Getty Images)

“This rain and snow bucked the trend, and it’s highly unexpected,” said Ryan Maue, a meteorologist and former National Oceanic and Atmospheric Administration chief scientist. (Image: Getty Images)

In California, the extreme weather has left thousands without power, closed Yosemite and Joshua Tree national parks, and led to avalanches. (Image: Getty Images)

Officials in tourist spots in the Sierra Nevada have urged visitors to stay home rather than risk travel as roads remain dangerous in the wake of snowfall. (Image: Getty Images)

Bianca Feldkircher, a meteorologist for the National Weather Service, said a persistent blocking pattern over Pacific Ocean along with cold air migrating south from the Arctic have created the conditions for widespread snowfall along the west coast. (Image: Getty Images)

“Not only were you getting significant snowfall in areas that already see snow, you were also seeing snowfall on lower elevations in southern California, which is super rare,” said Feldkircher. (Image: Getty Images)