A powerful storm that dropped up to 20 inches of snow in parts of Colorado knocked out power Monday to thousands of people, closed a lengthy stretch of a major highway and triggered rock slides in the foothills.

A 73-year-old Denver (search) woman died after a tree limb snapped off and struck her, while an elderly man who got lost while snowshoeing was found safe after a night outdoors.

Authorities said 150 miles of westbound Interstate 70 was closed from the Kansas line to Denver. The entire highway was closed for the 80 miles between Denver and Limon, where truck stop parking lots were overflowing.

More than 70 people were staying overnight in four Red Cross (search) shelters opened for drivers stranded along I-70, spokesman Robert Thompson said.

The storm cut off power to 50,000 homes and businesses when power lines snapped and transformers failed, Xcel Energy (search) spokesman Tom Henley said.

"You could hear them popping," said Tom Hartman, who was shoveling snow outside the Schlessman Family YMCA in Denver when the transformers began to crackle and die.

Some 33,000 homes and businesses, mostly in the Denver area, were still without electricity late Monday.

Dozens of schools closed or were opening late, including three in the Denver area that closed because of power failures.

Two children were hospitalized with minor injuries after a school bus slid backward down a steep embankment south of Denver, Douglas County schools spokeswoman Carol Kaness said.

The woman killed by the falling tree limb Monday was identified by the Denver Post as Virginia "Ginny" McKibben, a former reporter for the newspaper.

The unidentified 74-year-old man who got lost while snowshoeing with his son Sunday was found safe after a night outdoors in the foothills outside Denver.

"He's fine, he's just cold," Clear Creek County sheriff's dispatcher Marty Writer said.

Hundreds of flights were delayed at Denver International Airport as planes lined up to de-ice before takeoff, an airport spokesman said. At one point, the Federal Aviation Administration (search) grounded all Denver-bound flights for 90 minutes.

In southwestern Colorado, rain associated with the storm system was believed to have triggered two rock slides in San Miguel County, including one that shut down a lane of Colorado 145 near Telluride. No injuries were reported. Steady rain also caused two rock slides in Boulder Canyon northwest of Denver, forcing the closure of one lane of Colorado 119 and damaging a car. No one was hurt.

The National Weather Service had predicted up to 4 feet of snow in the southern Colorado mountains, but some of the snow melted and the precipitation turned to rain, leaving an accumulation of about a foot.

Snowfall amounts ranged from 20 inches in Breckenridge (search) to 12 inches in Strasburg, about 20 miles east of Denver. Ski resorts, eager to open for the year, reported up to 24 inches of snow in the mountains west of Denver.

El Paso County Search and Rescue was called to help drivers who got stuck on snowy county roads east of Colorado Springs.

"We've got people out trying out the four-wheel-drive vehicles, and they're finding out they don't work very well," spokesman Steve Sperry said.