Every so often, reminders of the enduring impacts of California’s Gold Rush pop up in unusual places. While the media has covered multiple stories about people and pets, and even horses and cows, that have fallen into or become trapped in historic abandoned mines throughout California, not all such events have resulted in rescues, injuries, or fatalities. For example, in 2010, a 200-foot deep mine shaft opened under a baseball diamond in Calaveras County. In 2016, a 35-foot deep shaft opened under a sports field at an elementary school in Grass Valley.
A few weeks ago, two slumping spots on a well-traveled road in Nevada County were also linked to century-old mines.
In each case, DOC’s Division of Mine Reclamation’s Abandoned Mine Lands Unit (AMLU) provided emergency funding to help local authorities deal with the issues before anyone got hurt.
Mining is integral to California’s history, but it also left tens of thousands of legacy mines blasted open then hastily abandoned before the advent of permits and reclamation requirements created to prevent safety hazards and/or environmental contamination.
AMLU was established in 1997 to locate and warn the public about the dangers of abandoned mines on public lands, gather information about the cultural significance of the sites and potential wildlife, assess the physical or environmental risk each poses, prioritize the need for remediation based on the type of mine hazard and its accessibility, and work with appropriate public agencies to eliminate dangerous mining features, such as shafts and old structures.
AMLU received a report on June 3 that an abandoned mine shaft had opened under LaBarr Meadows Road just south of downtown Grass Valley, creating an axle-bending bump. The thoroughfare is the original route from the town to nearby mines. The Nevada County Department of Public Works placed a metal plate over the hole, but the asphalt continued to sink. County officials requested AMLU’s help to identifying any legacy abandoned mine features involved and financial assistance with the remediation.
As AMLU was finalizing the paperwork for a $25,000 emergency contract, county staff discovered a second area of subsidence along the shoulder of the same road about half a mile to the south after someone stuck a wooden post into the pothole to warn motorists.
Utilizing old maps, AMLU determined that both issues were legacy mine-related. Records showed a vertical mine shaft near the first location known as the Diamond Mine. The second hole seemed to be associated with the Bullion Mine, and AMLU created a second $25,000 emergency contract.
By June 27, both mine-related holes had been addressed and the road re-paved. It’s unclear what triggered the subsidence, although county-contracted engineers theorized that significant winter rain may have loosened the underlying dirt while high temperatures softened the asphalt, causing it to sink into the ground.
“That isn’t uncommon in this area,” AMLU manager Cy Oggins said. “Both the Nevada County staff and the county’s contractor say that they get calls about this kind of thing about once a month, but most of it’s on private land, so we don’t hear about it. But we’re always ready to lend a hand when we can.”