At least eight people are dead and many more are still unaccounted for after nearly a week of heavy rains and catastrophic floods that devastated communities along Colorado’s Front Range and northeastern plains.

Tens of thousands of people were evacuated from towns cut off by rising rivers and streams, many by helicopter and National Guard convoys. Cities became islands, cut off on all sides by downed bridges, flooded highways and mudslides. Chinook helicopters rescued hundreds of residents from Lyons, Jamestown and other foothill areas inaccessible by car.

But those airlifts were halted on Sunday because of heavy fog and more rain, which kept the choppers grounded. Public safety officials were conducting house-to-house searches, looking for stranded and disabled residents.

Boulder County Sheriff Joe Pelle said in a statement released over the weekend, “Finding the people who are unaccounted for is one of the highest priorities.”

In some areas, people hiked out, climbed to higher ground or rode all-terrain vehicles to safety. Rescue crews used hastily rigged zip lines to transport marooned residents one by one across surging rivers and streams. Near Lyons, north of Boulder, several groups escaped on pack mules and horses. More than 2,000 people were evacuated from the canyon areas alone over the weekend, and 1,200 were stranded in Pinewood Springs, east of Estes Park.

The Denver area was spared the brunt of the damage, but Saturday storms left hail a foot deep in Aurora, and thousands were without power from Pueblo to Fort Collins.

Colorado Gov. John Hickenlooper (D) declared 14 counties disaster areas, and the Obama administration authorized federal disaster funds. “We’re still trying to evacuate people,” Hickenlooper said on Sunday. The governor’s own helicopter helped evacuate a stranded family during a weekend flyover to survey damage. “This is a heck of a storm. We’ve got a lot of broken roads and bridges, but we don’t have any broken spirits,” he tweeted afterward.

The storms’ impact was felt from Pueblo County in the south all the way to the Wyoming border as record rainfalls swept northward across the state, but cities nearest the foothills and those along the major waterways on the eastern plains were hit hardest. The series of monsoonal storms dumped more than 21 in. of rain across the region in a matter of days.

On Saturday, the floodwaters moved beyond foothill communities onto the eastern planes as debris-gorged tributaries filled the South Platte River to 50 times its normal capacity for September. Towns as far east as Fort Morgan and Sterling on the South Platte were inundated with floodwaters that clogged streets, closed county roads and buried thousands of acres of farmland.

Scores of livestock were stranded or drowned and several oil-and-gas drilling operations were disrupted as the waters rose. The South Platte, which usually flows at two to three feet during summer, surged to more than 13 ft deep.