Temperatures reached the low 20s in the San Francisco Bay Area.
In the East Bay city of Walnut Creek, the National Weather Service reported a 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.
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 late Saturday dipped to 30 degrees at Phoenix Sky Harbor International Airport and 25 degrees.
Low temperatures across Arizona included 23 at Tucson International Airport and 7 below in Flagstaff.