Scientists are scratching their heads over a crack in the Earth that’s more than half a mile long, Sky News reports. A drone captured video footage of the 16-foot-wide, 26-foot-deep crack, which appeared last week in remote farmland and cuts across Highway 26 between the coast and Hermosillo in northwest Mexico.

Some officials speculated a San Andreas Fault earthquake may have caused it—there was an earthquake along the fault on Sunday, First News notes—but experts at the University of Sonora are eying an underground stream as the possible culprit, Australia’s News Network reports.

The unstable ground is, however, forcing cars to drive around the area, and a second crack has reportedly opened up nearby. (Another geological marvel: water “missing for decades” is found 400 miles below the US.)