California was going from cold to colder Friday as a chill expected to bring the biggest mercury dips in years descended on much of the state.
The Grapevine section of Interstate 5, the key artery linking southern and northern California, was shut down Thursday night.
The area was blanketed with heavy snowfall that showed no immediate signs of stopping, leaving truckers and would-be travellers stranded.
Police said the closure would remain in effect overnight and the roadway would be re-evaluated in the morning.
The day saw several accidents and spinouts on the mountain pass that led to a pair of closures, the second of which continued into the night.
Elsewhere, strawberry growers covered their crops while San Diego zookeepers turned on heaters for the chimpanzees.
Forecasters warned that a low pressure trough sinking over San Diego County and parts of neighbouring Orange County could keep nightly temperatures below the freezing point in coastal areas, the low deserts and inland valleys, threatening orange, avocado orchards and other sensitive plants.
The coldest nights were expected to hit Friday and Saturday.
Farmers were prepared to pull out giant fans to circulate the air and keep it from settling on their citrus trees, said Eric Larson of the San Diego County Farm Bureau.
Other growers were placing soft cloth over their strawberries and flowers.
The National Weather Service predicted overnight lows in the 20s in the lower deserts and key citrus-growing regions in the Central Valley, and in the 30s along the coast.