Crescent City, site of a deadly tsunami four decades ago, appears to be particularly hard hit.
Local residents reported that about three dozen boats were "crushed" in the harbor and that surging waters significantly damaged or destroyed most of the docks. Ocean water surging up Elk Creek north of the harbor reportedly lapped up to front doors of the community's cultural center.
Officials were warning residents to expect higher surges throughout the day, one resident said by telephone. Officials from the local sheriffls department and the city could not be reached. Crescent City, near the Oregon border, was the scene of a devastating tsunami in 1964, which killed 11 people and destroyed 289 homes and businesses.
In 2006, tsunami-driven currents caused $10 million in damage to the city's harbor. One resident said Friday's damage to the harbor was as bad — or worse — as then.
Videos of the earthquake
Officials reported waves of 6 1/2 feet in Crescent City and 6 feet in Morro Bay, said Caltech scientist Lucy Jones.
Jones said officials won't know the extent of the damage until high tide occurs later Friday morning.
"Clearly, very large drawdown of water in Half Moon Bay," Jones said earlier in the day. "We are coming to high tide in a couple other hours. As long as we're still growing on tide, we need to keep a watch on the water. ... Currents may be very significant.
In Santa Cruz, the waves josted boats and damaged docks.
Authorities issued an evacuation advisory about 6:40 a.m. for coastal residents and those living along the San Lorenzo and Capitol rivers and other major waterways in Santa Cruz County, said county spokesman Enrique Sahagun.
The first waves reached land about 7:45 a.m. At Santa Cruz Yacht Harbor, the swells pushed and bumped boats together and broke some docks, but total damage is unknown thus far, Sahagun said.
"The water is pushing the boats together like a major car collision on Highway 405 or another big highway," he said.
Photos: Scenes from the earthquake