The situation has gotten 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.