A foothills fact of life, sudden cave-ins like the one that led to the death of 32-year-old Jason Chellew in Alta are often-dangerous remnants of California's gold-mining past.

Chellew died Friday after a cave-in that dropped the basement floor in the home he was living in about 20 feet.

Doug Craig, chief of the state Office of Mine Reclamation, said Wednesday that mine cave-ins close to or under structures and other accidents associated with the abandoned mines which honeycomb many areas of the Sierra and foothills are a natural outcome of the increase in people moving to the area.

The Sacramento-based reclamation office endeavors to collect old and new accounts of mine encounters but, until this weekend, had never come upon a fatal cave-in similar to the one in Alta, Craig said.

"It was a unique situation in Alta," Craig said.

Two incidents in 1998 illustrate that the Alta cave-in, while unique in it resulted in Chellew's death, wasn't an isolated incident. Office of Mining Reclamation records show a 30-foot shaft under a carport caving in at a home in Oroville that year. Two months later, a 30-foot deep pit opened at the front doorstep of a newly constructed home near Grass Valley.

In 1999, an abandoned underground mine in Colfax caved in, taking a tree down into the chasm. Two years later, a nursing home was evacuated after a cave-in at an abandoned mineshaft in Placerville.

Estimates by the Office of Reclamation put the number of abandoned mines in California at between 29,300 and 69,800 - with many unmapped and unknown to state record keepers.

"The old-timers are gone," said 84-year-old Mel Henderson of Grass Valley. "And there's not much evidence unless you find a portal or shaft. There's little to give you insight to build or not to build."

Henderson has been mining underground for 60 years, mostly in the Iowa Hill area.

Underground, miners search for ancient river beds to follow, sinking shafts sometimes 800 feet down or more to hit bedrock and dig along what was once a waterway. A large room underground would be built and then tunnels would be dug from there. Sometimes the timber support structure would be extensive, Henderson said. Sometimes it wasn't.

While hardrock mining provided its own support structure, so-called gravel mining dug into dirt, clay and rock deposits to find gold. Alta and Dutch Flat gravel mining in the 1800s could lead to depressions and cave-ins today - circumstances that could only be exacerbated this year by heavy rains weighing down surface soils and creating more crushing weight, he said.

In Auburn, Public Works Superintendent Sonny Harris said the city has experienced some recent cave-ins but they were due to some of the community's older wastewater lines failing. One involved a garbage truck on East Placer Street in downtown Auburn. A garbage truck ended up sinking a short depth into a collapsed portion of road but nobody was injured.

The city has its share of abandoned mines, with several shafts discovered in recent years off Auburn Folsom Road when the Vintage Oaks subdivision was built, he said.

Craig said that while it's difficult to identify whether a dangerous mine is located underneath a building site, precautions can be taken to help identify an area that could be a candidate for a collapse.

A Realtor or seller would have to disclose whether a possible hazard like an abandoned mine is located on the property, assuming they know of it, he said.

The county assessor could have information on mining claims and activity in an area, including maps, Craig said.

The California Geological Survey has a library with mining information from around the state including mineralogist reports from individual counties showing mining activity.

A walk-through on the site could also turn up evidence of disturbances or past mining activity. A geologist could also be hired to take a more expert look at the land, Craig said.

Property owners who find abandoned mine entrances or shafts on their land should report it to the Office of Mine Reclamation and tape off the area to keep people away, he said. The toll-free number is 1-877-OLDMINE.

The Journal's Gus Thomson can be reached at gust@goldcountrymedia.com.