DENVER (AP) - National Guard helicopters dropped emergency food bundles and bales of hay for people and livestock trapped by snowdrifts as high as rooftops Tuesday after back-to-back blizzards paralyzed the Plains.

At least a dozen deaths were blamed on a weekend storm that knocked out electricity to tens of thousands of people in Colorado, Kansas, Nebraska and Oklahoma and left herds of cattle without food. The blizzard spread a blanket of snow on top of the icy layer left by a storm just before Christmas.

Because of rising temperatures, many highways were clear, but many rural roads remained impassable, and National Guardsmen used Humvees and snowmobiles to reach people trapped in their homes and take them to shelters.

Colorado also launched a haylift in hopes of saving thousands of cattle immobilized by drifts as high as 10 feet. In 1997, a similar storm killed 30,000 in the state.