High arsenic readings close hiking trails in the Black Mountain Open Space

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SAN DIEGO – Some hiking trails in the Black Mountain Open Space Park between 4S Ranch and Rancho Penasquitos were closed this weekend after city officials discovered higher than normal arsenic readings at an abandoned arsenic mine.

Trails in close proximity to the mine were closed Friday to allow researchers to conduct further testing, sampling and monitoring of the mine and trails in the area. Public access to the mine and surrounding area is prohibited, including a portion of the Miner’s Ridge Loop Trail, city officials said.

Research and thorough testing was expected to take several months, so hikers were advised to follow all signage and ranger instructions in the park.

There is no conclusive evidence that there has been or is an imminent threat to the health of the public, plants or wildlife in and around the mine or along nearby trails as a result of this discovery, officials said.

The Black Mountain Arsenic Mine is located on the north slope of Black Mountain at an elevation of 1,000 feet and was mined for naturally occurring white arsenic in the 1920s for about eight to 10 years.

Many remnants of the mine operation still exist on the site, but the mine has not been in use for more than eight decades and there are no designated trails that lead the public to the mine in the open space.

Access to Black Mountain Peak is still available to the public along with western portions of the park, and rangers will continue to patrol the area as before, officials said.

An updated map indicating the locations of the trail closures is available to the public at Black Mountain Open Space Park as well as online at https://www.sandiego.gov/park-and-recreation/parks/osp/blackmtn/.