The discovery of the bodies of 58 men and 14 women came about when marines manning a checkpoint on a highway in northern Tamaulipas state were approached by a wounded man who said he had been attacked by cartel gunmen at a nearby ranch.
The man was placed under the protection of federal authorities. Navy aircraft were dispatched to the scene, and when the gunmen saw them, they opened fire on the marines and tried to flee in a convoy of vehicles.
It was unclear whether the victims had been killed at the same time or separately, and the navy did not say when they were found.
In May, authorities discovered 55 bodies in an abandoned mine near Taxco, a colonial-era city south of Mexico City that is popular with international tourists.
More than 28,000 people have died in drug-related violence in Mexico in recent years.