The Mississippi River
The Mississippi River is the East boundary for Arkansas.
The Mississippi River is the border separating Tennessee and Arkansas.
The natural boundary that separates New Jersy from Pennsylvania is the Delaware river
the equator...... i think
Tien Shan Mountains
The Ural Mountains.
Fall Line :)
The Pyrenees Mountains.
A reef or low island.
The Rio Grande river. The Rio Grande, or Big Rivernew london
Arkansas is located on a fault line called the New Madrid fault line also many small earthquakes recently have been caused by natural gas drilling.
Nature has provided the Pyrenees Mountains as the boundary between France and Spain.