Authorities said that at about 9:30 p.m Friday, the 32-year-old man was in a basement apartment in a section of the house that had recently been converted when the foundation suddenly snapped and opened up.
He fell into the hole and was covered by debris.
Emergency crews reached him but found no sign of life. It appears the sinkhole is getting bigger, and emergency crews said the house was too unstable to let a recovery team in.
"According to geologists in the area, they have determined that there is still movement occurring in the hole," said Jeff Brand of the California Department of Forestry. "The hole was initially eight to 10 feet deep, 10 feet in diameter and with remote cameras, we have determined the hole [is now] 30 feet in diameter and well over 20 feet deep."
Officials have not yet determined what caused the sinkhole. They are looking into a range of possibilities including whether the recent rains softened the ground under the home or that the house is built over an unknown, abandoned mine shaft.
A local historian says there are no maps showing where the shafts and tunnels are located in and around the town of Alta.
However, the Nerry Red Placer Mine operated in the area in the 1870s. The 224-acre mine had 16 named claims all mined by different people. The home with the sinkhole is in the old mining boundaries.
The man's name has not been officially released but neighbors believe he is Jason Chelew, the son of a retired California Highway Patrol officer. Chelew was married and his wife is expecting their first child.