Together they form a "vast (more than 300 km2 (120 sq mi)) and extremely diverse area of western substeppe ilmens (WSI)" which, because of the varying degrees of wetness and salinization, house a wealth of flora and fauna.[3] The origin of these mounds and ilmens is still debated: the early suggestion that they were formed by aeolian (wind) action is now discredited, and now they are thought to have arisen either underwater or through river flow.[4]