LOS ANGELES (AP) -- Some normally warm California spots shivered Sunday as early morning temperatures plunged, leaving even polar bears at the San Diego Zoo seeking shelter. But growers in the Central Valley were relieved to learn most orange and lemon crops probably avoided significant damage despite temperatures in the high 20s.

"We were just a little bit colder, by a degree or two," said spokesman Paul Story of California Citrus Mutual, a growers' trade association. "For the navel oranges, that's not cold enough to do a measurable amount of damage."

He said more sensitive mandarin oranges may have suffered some minimal damage.

It was the third night of successful crop protection for farmers, who run wind machines and water to protect their fruit. Growers faced at least one more night of work as the forecast called for cold weather into Monday.

In the Los Angeles area, famously torrid Woodland Hills, which usually makes news for its triple-digit temperatures, had an overnight low of 30 degrees. That was warm compared to Lancaster in north Los Angeles County, which hit 15 degrees.

Temperatures reached the low 20s in the San Francisco Bay Area.

In the East Bay city of Walnut Creek, the National Weather Service reported an overnight low of 23 degrees, while in the Santa Clara County community of Scotts Valley, the temperature dropped to 26.

Meanwhile, in the Sierra Nevada, temperatures plunged below zero overnight, and after a day in the 20s, another subzero night was expected.

In San Diego, zookeepers offered extra heat and shelter for some animals, including polar bears. While the bears tolerate frigid climes, the zoo animals lack the fat layers that naturally occur in the wild and protect them from the cold. So, zookeepers offer them "warming apparatuses," zoo spokeswoman Jenny Mehlow said.

"The animals do take this in stride because they're wearing a nice, warm fur coat," she said.

The cold air was flowing east into neighboring Arizona, where metropolitan Phoenix was approaching the halfway point in a four-day cold snap that's expected to mark the coolest stretch the area has seen since 1988. Temperatures on Saturday night dipped to 30 degrees at Phoenix Sky Harbor International Airport and 25 degrees.

Low temperatures across Arizona on Saturday night included 23 at Tucson International Airport and 7 below in Flagstaff.

Copyright 2013 The AP.