Parts of the state are expected to be hit by up to eight feet of snow and a foot of rain, prompting fears of mudslides.
The threat of heavy downpours and up to eight feet of snow has left residents in California "in a state of panic", officials have said.
The northern part of the US state is expected to be battered by heavy storms over the weekend, prompting flash flood warnings and fears of mudslides.
Forecasters say the adverse weather is being caused by an atmospheric river - a thin corridor of moisture originating in the tropics.
This is expected to bring up to a foot of rain in Santa Cruz, west California, where sandbags have been handed out to residents.
Meanwhile, up to eight feet of snow is expected to fall around Mammoth Lakes in the east.
El Dorado County sheriff's sergeant Todd Hammitt said the forecasts had alarmed those who live within affected areas.
"People are definitely in a state of panic right now," he told the LA Times. We're getting a lot of calls asking if we're going to be able to deal with everything.
"It's the general pandemonium of not knowing what's coming."
He said the state was expecting "heavy, heavy rain".
"It starts out as snow then turns to rain then turns to snow again," he said.
"We have streams, creeks, rivers. We have lakes and ponds. Anybody near a water source could be in jeopardy depending on the severity of the storm."
California has endured five years of drought but has experienced storms with heavy rains since October.
On Friday evening, access to the valley of Yosemite National Park was closed as adverse weather conditions began to set in.
The Truckee River, which flows from Lake Tahoe to Reno in Nevada, is forecast to rise to its highest point in more than a decade.
Meteorologist Zach Tolby said: "This is a classic set up for us for flooding. We're definitely expecting a very wet weekend."