The 26-foot-deep crack stretches for nearly two-thirds of a mile near the Sonora state capital of Hermosillo.
It blocks traffic on federal Highway 26 between that city and the Gulf of California port of Bahia de Kino.
Civil protection officials believe an earthquake is responsible for the fissure, but University of Sonora geologists say a subterranean stream could have undermined the ground.
They believe the stream was created when a levee built by local farmers sprang a leak.
A video of the massive crack, captured by a drone, shows it is wide enough to swallow a truck.
Photo: Hermosillo Desde el Cielo