Officers of the Policía de Fronteras came upon sacks of buried weaponry Monday night on the Isla Calero in extreme northeast Costa Rica.
That is the area that was invaded and occupied by Nicaragua in 2010.
The weapons probably are leftovers from the Nicaraguan civil war rather than the more recent incursion.
The find included six Belgian-made FAL semi-automatic rifles. There also were six AK-47 rifles and a .30-caliber rifle.
All were in sacks that had been hidden in the ground. All the weapons appeared to be rusted beyond salvage. Police said they would be destroyed.
The AK-47 of Eastern European manufacturer wasa ffavoriteof the conflict that pitted the U.S.-based Contras against the Nicaraguan Sandinista government from 1979 to the early 1990s.
Costa Rica spend years eliminating the land mines that had been planted in national territory during that conflict.