Pacific storm brings more rain and snow to the already saturated US west coast.

Rising flood waters turned the Northern California community of Guerneville in the United States into an island on Wednesday.

Water rose to the roofs of homes and submerged cars as the rain-swollen Russian River overflowed its banks.

Starting on Tuesday, authorities began the evacuation of over 4,000 Guerneville residents, asking them to leave their homes or risk being stranded for days

On Tuesday afternoon, a large mudslide in the town of Monte Rio, California closed both lanes of the Bohemian Highway, cutting off its main southward route.

The community there is also at risk of flooding from the rising Russian River.

By Wednesday afternoon, the river had risen to over 13 metres, well above flood stage, and by midnight had crested at 13.8 metres.

Since Tuesday, the recent Pacific storm has brought over 132 millimetres of rain to the already saturated parts of Northern California. This winter has been particularly wet already with dozens of Pacific storms coming onshore since December.

The heavy rainfall was only part of the story. In the higher elevations of Sierra Nevada, heavy snow crippled travel in some areas. Highway 80, which crosses from California to Nevada, was closed for a 120-km stretch because of the dangerous driving conditions.

On the rails, Amtrak suspended passenger trains between Sacramento and Reno because of an avalanche at Donner Pass. Service was unlikely to resume anytime soon.

Even though much of the rain has now moved east, flood warnings are still in effect through Friday for much of Northern California as runoff continues to flow downstream.