SAN DIEGO -- A surprise snowstorm left hundreds of motorists stranded overnight on a frozen stretch of Interstate 8 in the East County highlands, according to the California Highway Patrol.

The CHP shut down about 60 miles of the freeway late Thursday afternoon during heavy snowfall that blanketed areas as low as 2,000 feet above sea level.

The nearly 20-hour emergency closure between Willows Road in Alpine and the Imperial County line left as many as 500 vehicles stuck for a time in the frigid highlands east of San Diego, officials said.

Some were able to take shelter at Golden Acorn Casino in Campo and the Pine Valley Fire Station.

On Thursday night, Highway Patrol personnel came to the aid of drivers waylaid within the cordoned-off section of interstate, CHP public affairs Officer Rob Sanchez said.

Early Friday, officers began escorting motorists parked against their will on the freeway west of the roadblocks, according to Sanchez. Small clusters of vehicles followed CHP cruisers out of the area over Willows and Crestwood roads.

Icy road conditions forced that process to a halt around 6 a.m., until the morning sun melted enough of the ice to allow for safe driving.

The entire freeway was open again under clear skies by noon, Sanchez said.

The National Weather Service had not predicted the storm, which began with light scattered showers early Thursday, then turned into heavy rain, hail, sleet, snow and lightning throughout the county.

Some locales unaccustomed to snowfall got considerable amounts of it, including 2 1/2 inches reported in Ramona and 5 inches in Campo, which is about 2,500 feet above sea level, said Noel Isla of the Weather Service.

He said it was unusual for snow to fall at that low an elevation in the San Diego area, but could not immediately say the last time it snowed there.

Most of the snow was gone by Friday afternoon, he added.

On Thursday, major afternoon flooding and mudslides shut down State Route 76 between SR-79 and Valley Center Road, and SR-78 between Ramona and Escondido.

SR-76 has since been reopened, while SR-78 will remain closed until Saturday, officials said.

The storm developed when a low-pressure system from the northeast made an unanticipated push into Southern California, where it merged with a thick marine layer, according to the National Weather Service.

No more precipitation is in the forecast until Tuesday night. Barring any more surprises, the weekend should be sunny with light winds, forecasters said.