The storms have flooded streets, shutting down some of the state's most critical motorways, with footage on social media showing fallen trees and inundated neighbourhoods.
Downed power lines left thousands without electricity as crews raced to remove live wires from roads and broken tree branches. A sinkhole in Orange County sucked in two vehicles and boulders crashed on to cars parked along the Pacific Coast Highway, blocking the streets of Malibu.
Crews raced going door-to-door, warning residents of mudslides and pulling stranded pets from flooded homes.
The latest atmospheric river — a storm that dumps tremendous amounts of rainfall — has eased in some areas, with the storm shifting to Northern California.
An “enormous cyclone” coming off the West Coast is forecasted to bring even more rain and heavy winds to the northern part of the state as well as the Pacific North-West in the coming days.
The National Weather Service in a Wednesday morning advisory said the “endless stream of atmospheric river events” will refocus in Northern California and into Oregon and Washington state, sparing parts of Southern California and in particular Ventura County, which reported a record 48 centimetres of rain. Mammoth Mountain resort has received nearly eight metres of snowfall this year.
“The fact is that we're not out of the woods; we expect these storms to continue at least through the 18th of this month,” California Governor Gavin Newsom told reporters during a news conference on Tuesday.
“We now have 17 confirmed — and I underscore 'confirmed' tragically — just confirmed deaths.”
Santa Barbara County, two hours north of Los Angeles, lifted an evacuation order that affected about 10,000 people, including the wealthy enclave of Montecito, home to celebrities such as the Duke and Duchess of Sussex, Oprah Winfrey, Jennifer Aniston and Carol Burnett.
The city's evacuation came on the fifth anniversary of mudslides that left 23 people dead and more than 100 homes destroyed.
Montecito is vulnerable to mudslides because it sits on a mountain front that was destroyed by a wildfire years ago.
Montecito deadly flood in 2018 - in pictures
The severe weather is the latest event to punish the state, which has experienced deadly wildfires and extreme heat in recent years due to global warming.
The storms could cost more than $1 billion, The Los Angeles Times reported — similar to damage costs caused by other extreme weather events that struck the US last year.
Despite the rainfall across the state, much of California remains in a moderate to severe drought, according to the US Drought Monitor.
“Megadroughts. Wildfires. Historic floods and atmospheric rivers. This whiplash weather is not an anomaly. California is proof that the climate crisis is real and we have to take it seriously,” Mr Newsom said in a tweet.
Search operations resumed for Kyle Doan, a five-year-old boy who was swept away by the floodwaters in Paso Robles earlier this week. The San Luis Obispo County Sheriff said finding the boy remains “our top priority”.
The boy's mother was driving when her vehicle became stuck in floodwaters on Monday morning. Bystanders were able to rescue the mother but the boy was swept away. Mr Newsom said he is praying for Kyle's safety.
US President Joe Biden approved an emergency declaration in California that will authorise federal resources to aid in recovery efforts.
Agencies contributed to this report