 The Erzi Reserve is in mountainous terrain on the north slope of the Caucasus.The Assa River (Sunzha River) and the Armkhi River run south to north through the reserve (the Assa is the western border), on their way to the Terek River which flows into the Caspian Sea to the east.Through the reserve just north of the main ridge (which is of shales and sandstones) of the Caucasus runs a lower, parallel ridge of carbonate rock called the "Rocky Ridge" ().