SAN FRANCISCO--Workers zeroed in on remaining bodies buried under tons of freeway concrete yesterday and scientists pinpointed the epicenter of the mammoth earthquake beneath a mountain creek while President Bush toured ravaged areas to offer sympathy and aid.

Damage estimates climbed over $4 billion throughout the 75-mile-long region, officials declared the ornate 78-year-old Oakland City Hall unusable, and 26 buildings were closed indefinitely at Stanford University near Palo Alto, 35 miles south of San Francisco.

So far, 43 bodies of quake victims have been recovered. Dozens remain listed as missing.

To make matters worse, rain and temperatures in the 30s were forecast for the area by today. Authorities said that could hamper rescue efforts.

"It depends on how hard the rain is. If it's not too hard we hope to be able to work through it," said Bob Jacobs, deputy district director of the California Department of Transportation.

Rain also heightened the threat of additional landslides in the mountains north of Santa Cruz, where 60 homes already have been destroyed in Boulder Creek, a town of 6,800.

About 100 residents were ignoring evacuation warnings.

"It's a dangerous area, but all my stuff is here. My dogs are here. I figured you go down with the ship. Where do you go?" asked Todd Viele.

Bush walked over chunks of concrete beside the 12-mile crumpled stretch of Interstate 880 in Oakland where scores of people were feared entombed and talked with rescue workers. He had said he hoped to offer encouragement.

"I am deeply moved by this, saddened in some ways, yet very stimulated by this team effort," the president said.

Administration officials worked on a program of aid as the president made his trip. Transportation Secretary Samuel Skinner offered no pricetag but said the federal government would take on "a very, very major role in helping California."

A moderate aftershock registered 3.9 on the Richter scale at 1:13 a.m. yesterday, centered about seven miles southwest of Los Gatos, University of California at Berkeley seismologists said. It was felt north and south of San Francisco.

More than 1500 aftershocks have hit since Tuesday.

Scientists roaming through mountains southeast of San Francisco pinpointed the epicenter of Tuesday's 5:04 p.m. killer quake in the northeast corner of the Nisene Marks State Park, near the top of Aptos Creek, said Joseph Cotton with the U.S. Geological Survey in Menlo Park.

That's about 57 miles from San Francisco atop the San Andreas Fault, and just 14 miles northeast of hardhit Santa Cruz, where 10,000 people are reported displaced from their homes.