Landscape architect Walter Guthrie was buried under tonnes of rock, dirt and trees while he cleared a drain behind his Northern California house, according to emergency workers who dug for more than 24 hours to find him.
The mudslide that killed the 73-year-old man crashed through the rear wall of his house in Mill Valley just north of San Francisco.
A relentless series of soggy storms has drenched the region for more than a month, breaching levees, dangerously filling waterways, and causing hillsides to slip.
A duplex that had been evacuated because a hillside in the city of Rio
Vista was giving way crashed down the steep incline. Elsewhere, landslides closed roads.
California Governor Arnold Schwarzenegger declared parts of the state emergency zones after a brief helicopter tour of the levee system on Thursday.
"I'm a hands-on governor," Governor Schwarzenegger told reporters during the tour. "I want to see first-hand that the levees are being shored up."
In his emergency proclamation, Governor Schwarzenegger wrote that "conditions of extreme peril" existed in counties such as Marin, where Mill Valley is located.
While a break in the storms had eased the threat of flooding, waterlogged hillsides and earth levees remain at risk of giving way, according to emergency officials.