Most of the interfluve lies in Kazakhstan, within the
West Kazakhstan Region and
Atyrau Region. From south it is bordered by the
Caspian Sea, into which both Volga and Ural flow. The southern arid area is within the
Caspian Depression,
Caspian lowland desert ecoregion. It rises gradually from the sea coast northwatrds, with averaged elevations in the lower area ranging between 28 m and 11m below sea level. In the vicinity of
Volga Delta there are groups of with heights up to 25 m. Between them freshwater bayous and saltwater lakes may be formed. The latter can dry out and form salt-covered depressions. The whole shore of the Caspian sea is fringed with a strip salty sands cut with bayous filled with seawater when the wind blows from the sea (this kind of winds is called "moryana" (
:ru:моряна) in Russian, form the word
more, "sea"). There is also a large number of small
intermittent and some larger permanent saltwater lakes in the southern desert area. The most notable of them is
Baskunchak, with major
salt mining. Within the confines of
Atyrau Region, Kazakhstan, bordering the
Astrakhan Oblast, Russia, there is a huge sand massif formerly known as "Urdinskiye peski" (Урдинские пески), now "Ryn-peski", or
Ryn Desert. The northern part belongs to the
Pontic–Caspian steppe ecoregion. The
interfluve may be divided into the following zones: plain clayey steppes zone, plain sandy desert zone, plain clayey desert zone, plain sandy desert steppe zone. ==History and archaeology==