Los Angeles, California (CNN) -- A strong storm system made driving dangerous in the Rockies and the upper Plains and contributed to a pileup involving about 100 vehicles Thursday near Fargo, North Dakota, officials said.

"It is not fit for anyone to be out there," North Dakota State Highway Patrol Capt. Eldon Mehrer told CNN radio.

Snow, ice and rain plagued much of the West, and North Dakota officials closed Interstate I-94 between Jamestown and Fargo and the north-south Interstate 29 from the Canadian border to South Dakota.

The I-94 chain-reaction wreck a few miles west of Fargo occurred when two semi trucks jackknifed in the treacherous conditions, Some 100 vehicles were affected by the mishap, with about 30 involved in crashes.

One person was critically injured amid four injury incidents, Mehrer said.

Clearing the accident was difficult, said the patrol officer, who had a simple message to motorists: stay home.

Across much of the state, rescuers gave up trying to get vehicles out of ditches and concentrated on picking up stranded motorists using snowmobiles and buses.

In California, acting Gov. Abel Maldonado declared a state of emergency for Mariposa County Thursday because of extreme weather and storm conditions.

The central California community becomes the 12th California county declared to be in a state of emergency because of this month's punishing rain and windstorms. The others are Kern, Orange, Riverside, San Bernardino, San Luis Obispo, Tulare, Kings, Los Angeles, Santa Barbara, Inyo and San Diego counties.

Officials in Mariposa County, which describes itself as the home to Yosemite National Park, had earlier declared a local emergency, Maldonado said in the proclamation.

This month's winter storms have been so punishing that the flood damage to homes, businesses and roads require "the combined forces" of state and regional aid for providing relief, the proclamation said. Maldonado is serving as the chief executive while Gov. Arnold Schwarzenegger is away from the state on vacation.

Meanwhile, a missing snowboarder who had been enjoying the fresh snow was found dead Thursday morning in the Alpine Meadows ski resort in Tahoe City, California, said resort spokeswoman Rachael Woods.

Shawnte Willis, 25, of Tahoma, California, had been missing since Tuesday when snowboarding with friends, and her body was found in a tree well about 400 feet below the Pacific Crest Trail in the Granite Chief Wilderness Area by search and rescue team supervised by the Placer County Sheriff's Department.

A series of Pacific storms have created the wettest December ever throughout southern California, according to National Weather Service recording stations in Los Angeles, Long Beach, Camarillo, Santa Barbara and Santa Maria.

Arizona was rebounding Thursday from the storm, with I-17 and I-40 open in both directions. Crews were using de-icers to keep them safe, officials said.

"We think we passed the worst of it," said Department of Transportation spokesman Timothy Tait, indicating clear skies Friday will help after a frosty overnight.

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Snow, ice and low visibility snarled traffic, and parked cars made it difficult for some of the nearly 300 state snowplows to do their work, Tait said. Suburbs of Phoenix reported flurries.

U.S.180 remained closed north of Flagstaff, and 89A between Sedona and Flagstaff was mostly out of commission.

This week's storms were also "a contributing factor" in the death of a 70-year-old woman in a northern California exotic wildlife preserve, authorities said Wednesday.

The woman was reading a bedtime story to her 7-year-old granddaughter Tuesday night when an oak fell on their safari-style luxury tent in Santa Rosa. The grandmother was killed instantly, authorities said, but the child was unharmed.

"Obviously, the weather was a contributing factor to this tragedy," said Cyndi Foreman, a spokeswoman for the Rincon Valley Fire Protection District in Santa Rosa. "It was heavy rain in a short period of time and heavy winds and back-to-back storms."

The death occurred as a strong and cold storm system from the Gulf of Alaska moved into the West. Ice was causing headaches in Arizona and the National Weather Service said additional rains, heavy snow and winds would make the going rough over the next several days for residents in much of the region.

Weather specialist Stuart Seto said this week's rainstorms, pushed by a cold front out of the Gulf of Alaska, didn't produce major debris or mudslides on Tuesday or Wednesday.

"It was a fast-moving storm, so we were lucky. No major debris flows (but) there were some little ones," Seto said.

The Alaskan front brought low temperatures to southern California Thursday and is expected to bring freezing temperatures to the Los Angeles suburb of Woodland Hills, which could see 31 degrees Friday morning, Seto said. The record low for that day was set in 1972 at 27 degrees, Seto said.

In New York, snowbound residents said their streets remained clogged days after a massive holiday blizzard.

New York City Mayor Michael Bloomberg said Thursday he will investigate whether sanitation workers intentionally delayed cleanup efforts over frustrations regarding citywide budget cuts.

The slow cleanup effort hampered morning commuters, delayed first responders and even prevented aircraft service personnel from reaching airports where 29 international flights were stuck on the tarmac for more than three hours, officials said.

CNN's Paul Vercammen and Phil Gast and CNN Radio's Barbara Hall contributed to this report.