LAKEPORT, Calif. - Scott and Robin Spivey had a sinking feeling that something was wrong with their home when cracks began snaking across their walls in March.
The cracks soon turned into gaping fractures, and within two weeks their 600-square-foot garage broke from the house and the entire property - manicured lawn and all - dropped 10 feet below the street.
It wasn't long before the houses on both sides collapsed as the ground gave way in the Spiveys' neighborhood in Lake County, about 100 miles north of San Francisco.
"We want to know what is going on here," said Scott Spivey, a former city building inspector who lived in his four-bedroom, Tudor-style dream home for 11 years.
Eight homes are now abandoned, and 10 more are under notice of imminent evacuation as a hilltop with sweeping vistas of Clear Lake and the Mount Konocti Volcano swallows the subdivision built 30 years ago.
The situation has become so bad that mail delivery was ended to keep carriers out of danger.
"It's a slow-motion disaster," said Randall Fitzgerald, a writer who bought his home in the Lakeside Heights project a year ago.
Unlike sinkholes of Florida that can gobble homes in an instant, this collapse in hilly volcanic country can move many feet on one day and just a fraction of an inch the next.
Officials believe water that has bubbled to the surface is playing a role in the destruction. But nobody can explain why suddenly there is plentiful water atop the hill in a county with groundwater shortages.
"That's the big question," said Scott De Leon, county public works director. "We have a dormant volcano, and I'm certain a lot of things that happen here (in Lake County) are a result of that, but we don't know about this."
Other development on similar soil in the county is stable, county officials said.
While some of the subdivision movement is occurring on shallow fill, De Leon said a geologist has warned that the ground could be compromised down to bedrock 25 feet below and that cracks recently appeared in roads well beyond the fill.
"Considering this is a low rainfall year and the fact it's letting go now after all of these years, and the magnitude that it's letting go, well it's pretty monumental," De Leon said.
County officials have inspected the original plans for the project and say it was developed by a reputable engineering firm, then signed off on by the public works director at the time.
"I can only presume that they were checked prior to approval," De Leon said.
The sinkage has prompted county crews to redirect the subdivision's sewage 300 feet through an overland pipe as manholes in the 10-acre development collapsed.
Consultant Tom Ruppenthal found two small leaks in the county water system that he said weren't big enough to account for the amount of water that is flowing along infrastructure pipes and underground fissures, but they could be contributing to another source.
"It's very common for groundwater to shift its course," said Ruppenthal of Utility Services Associates in Seattle. "I think the groundwater has shifted."