Denver ? A powerful storm that dropped up to 20 inches of snow in parts of Colorado knocked out power Monday to thousands of people, closed an 80-mile stretch of a major highway and trigged rock slides in the foothills.

Authorities said a 60-year-old Denver woman died after an 8-inch-diameter tree limb snapped off and struck her. No other details were available.

Authorities closed the main east-west route across Colorado, Interstate 70, from Denver east to Limon. Seventy miles of U.S. 24 from Limon southwest to Colorado Springs also were closed. A day earlier, the Red Cross opened a shelter for stranded travelers.

The storm cut off power to 25,000 homes and businesses in Denver when power lines snapped and transformers failed, Xcel Energy 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.

Power had been restored by Monday to about 2,000 homes and businesses in Breckenridge.