A string of Pacific storms brought more torrential rains and massive flooding.

Video posted to social media showed sidewalks turned into rivers.

Residents in San Bernardino tried to use sandbags to hold back the tide, with little effect.

At least 12 deaths have been blamed on the storms.

Forecasters with the National Weather Service warned this week a "relentless parade of cyclones" for northern and central California, promising little relief for the region until the middle of the week.

"So, Montecito is under complete evacuation, the entire town..."

Actress and former talk show host Ellen Degeneres tried to capture the extent of the devastation

"We are having unprecedented rain. This creek next to our house never flows, ever - probably about nine feet up, and it's going another two feet up. We have horses ready to evacuate. We need to be nicer to Mother Nature, because Mother Nature is not happy with us, Let's all do our part. Stay safe, everybody. Yikes."

Two overlapping phenomena - an immense airborne stream of dense moisture from the ocean called an atmospheric river and a sprawling, hurricane-force low-pressure system known as a bomb cyclone - have caused devastating flooding and record snowfall over the past week.

Black streaks of mud on a white garage door in Felton, California, show just how high the floodwaters rose as they rushed through this mountain town, inundating homes.

"It rose very, very fast. And when the alarm bells went for the flood stage, it was rising at about two feet per hour."

Camilla Shaffer used a garden rake to push mud and debris out of her home. She said she was lucky.

"Here we are fortunate that we are elevated. But we have neighbors in the Grove who haven't been so lucky. And it's been really devastating."

Authorities warned that parts of the California coastline are particularly vulnerable to potentially lethal mudslides after past wildfires stripped hillsides bare of foliage.

Rainfall throughout Tuesday was expected to be "heavy to excessive" across the state, especially in southern California.

The high winds have also wreaked havoc on the power grid, knocking out electricity to tens of thousands. Data from Poweroutage.us showed many as 220,000 homes and businesses were without electricity on Tuesday morning.