DENVER - Up to 15,000 cattle may have been killed by a snowstorm that buried southeastern Colorado under several feet of snow and built drifts up to 15 feet high, a Colorado Cattlemen's Association official said Monday.

That would be more than four times higher than the 3,500 cattle that state officials estimated were killed, but the smaller number included only range cattle and did not account for thousands of livestock in feedlot pens.

Terry Fankhauser, executive vice president of the state Cattlemen's Association, said he estimates between 10,000 and 15,000 cattle died. He said he based his estimate on conversations with ranchers and feedlot owners.

“We're waiting on pins and needles” to hear whether ranchers will receive federal disaster aid as requested by the state, Fankhauser said.

State officials have said many ranchers will not have an accurate count of their losses until more snow melts. Fankhauser estimated that up to one-third of ranchers in the area have not located all their cattle.

A storm that hit Dec. 28 left thousands of cattle stranded without food or water in the southeastern part of the state. Colorado National Guard troops used helicopters and large trucks to deliver hay to livestock.

By Monday, many roads had been made passable and ranchers were able to start feeding their own cattle after the second of three snowstorms to hit Colorado in two weeks, said Laura McConnell, a spokeswoman for a state team coordinating relief efforts.

Elsewhere, winds gusting to 115 mph Monday toppled trees, blew over an airplane and whipped old snow into ground blizzards that blinded motorists along the foothills of the Rockies.

Officials closed several roads during the morning rush, including a stretch of eastbound U.S. 36, the heavily traveled link between Boulder and Denver, and dozens of schools called off classes. Many roads had reopened by afternoon.

The National Weather Service issued a high wind warning for the foothills and central mountains from the Wyoming border to about 60 miles southwest of Denver. Much of the same area was also at high risk of avalanches as the wind created drifts on top of unstable snowpacks, according to the Colorado Avalanche Information Center.

Workers at the National Renewable Energy Laboratory's National Wind Technology Center about 20 miles northwest of Denver were unable to reach the site Monday due to poor weather to determine whether a 115-mph gust recorded at 2:30 a.m. caused any damage, said laboratory spokesman George Douglas. “One of the reasons the site is where it is, is to get wind extremes,” he said.

Gusts from 82 mph to 93 mph were reported elsewhere in Boulder and Jefferson counties, the weather service said.

About 12,000 people in the Boulder area and northern Colorado, lost electricity at some point Sunday night or early Monday due to the high winds, but repairs had restored power by afternoon, spokesman Mark Stutz said.

In Boulder, officials closed the city's airport after the wind overturned an unoccupied airplane that had been tied down, and snow drifted onto the runways. City crews were cleaning up numerous trees knocked down by the winds, city officials said.

Roads slickened by newly drifted snow were blamed for numerous traffic accidents, said Boulder County sheriff's Lt. Detective Phil West. He said no injuries were reported.

In Jefferson County, 18 people who were stranded in their cars Sunday were rescued by a Sno-Cat, and an unknown number of other motorists were rescued by deputies using 4-wheel-drive vehicles, sheriff's spokeswoman Jacki Kelley said Monday.

“Because of ground-blizzard conditions, they couldn't see,” she said. “Some literally couldn't ascertain where the road edge was. They chose not to (move) for fear of where their car would go.”

At Centennial Airport south of Denver, a twin-engine plane carrying two pilots and six passengers slid off a runway into deep snow Monday morning, causing some damage to the plane, said David Bowling, regional director of the National Transportation Safety Board. He said investigators will consider whether weather conditions contributed to the incident. No injuries were reported.

The winds began late Sunday and quickly overwhelmed plow drivers.

“The plows would run three blocks, do a loop around, and there would already be a foot of snow on the road,” Colorado Department of Transportation spokeswoman Stacey Stegman said.

CDOT spokesman Fritz Homann said it was the worst snow windstorm some highway department veterans could remember.

“Overnight, I was talking to our 14-, 15-year veterans who said they have never seen anything like this,” Homann said.

Thirteen Colorado counties - including the cities of Denver, Boulder and Pueblo - were included in the emergency declaration issued by Presiden Bush Sunday for the Dec. 18-22 blizzard. A second declaration was issued for Otero County in southeastern Colorado for the Dec. 28-31 storm, Federal Emergency Management Agency spokesman Jerry DeFelice said.

The action makes the counties eligible for reimbursement from the Federal Emergency Management Agency for 75 percent of costs for snow removal, police overtime, shelter operations and emergency medical care.

The declarations do not trigger low-interest loans to ranchers, nor does it provide for direct assistance to households or businesses, DeFelice said.

In southeastern Colorado, where Colorado National Guard troops and crews from several state agencies plowed roads and used helicopters and trucks to deliver hay to isolated livestock, counties were taking over more of the storm cleanup.

Crews were still delivering hay by ground, but most ranchers were able to start clearing some of their own roads and get to their cattle, said Laura McConnell, a spokeswoman for a state team coordinating relief efforts.

The next big concern is rounding up enough hay for area herds, said Scott Brase of the Colorado State University agriculture extension agency. He said most ranchers were short on hay because of the ongoing drought, and now the grass is under several feet of snow. The price of a ton of alfalfa hay has risen from $130 before the storm to more than $200 now, Fankhauser said.

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Associated Press writers Judith Kohler and Kim Nguyen contributed to this report.