Hamun Lake in the context of "Zabulistan"

The Gowd-i zerrah, i.e., Zerrah Depression (Persian for "lake depression") is the lowest part of an inland drainage basin covering large parts of southern Afghanistan and Iran known as the Sistan Basin. The Sistan Basin is an endorheic basin and encompasses a complex system of rivers, shallow lakes, marshes, and wetlands as its watershed, draining into the Hamun Lakes in southeastern Iran. Occasional outflows from these lakes are carried back into Afghanistan by the seasonal Shile River to the basin's terminus, the Godzareh depression in Afghanistan. The depression is flat and very shallow with fine-textured sediment at its lowest portions. The lowest section of the Godzareh depression is 467 m above sea level. The depression only receives runoff water when the main tributaries are overflowing every 10 years on average.

In general, a geological depression is a landform that is sunken or lower than the surrounding area. The Godzareh depression is the lowest point in the Sistan Basin in Afghanistan and therefore is the terminus to which all the water flows.

The Helmand river, also historically known as the Etymandros, is the longest river in Afghanistan and the primary watershed for the endorheic Sistan Basin. It originates in the Sanglakh Range of the Hindu Kush mountains in the northeastern part of Maidan Wardak Province, where it is separated from the watershed of the Kabul River by the Unai Pass. The Helmand feeds into the Hamun Lake on the border of Afghanistan and Iran.

Oshida or Mount Khwaja or Mount Khwajeh (Persian: کوه خواجه, romanized: Kuh-e Khājeh) is a flat-topped black basalt hill rising up as an island in the middle of Lake Hamun, in the Iranian province of Sistan and Baluchestan.

The trapezoid-shaped basalt lava outcropping, located 30 km southwest of the town of Zabol, rises to 609 meters above sea level and has a diameter ranging from 2.0 to 2.5 kilometres. It is the only natural height in the Sistan area, and is named after an Islamic pilgrimage site on the hill: the tomb and shrine of Khwaja Ali Mahdi, a descendant of Ali ibn Abi Talib.

Sistān (Persian: سیستان), also known as Sakastān (سَكستان, lit. 'the land of the Saka', current name: Zabol) and Sijistan (سِجِستان), is a historical region in south-eastern Iran, and extending across the borders of south-western Afghanistan, and south-western Pakistan. Mostly corresponding to the then Achaemenid region of Drangiana and extending southwards of the Helmand River not far off from the city of Alexandria in Arachosia. Largely desert, the region is bisected by the Helmand River, which empties into the Hamun Lake, located in Zabol, that forms part of the border between Iran and Afghanistan.

Drangiana or Zarangiana (Greek: Δραγγιανή, Drangianē; also attested in Old Western Iranian as 𐏀𐎼𐎣, Zraka or Zranka, was a historical region and administrative division of the Achaemenid Empire. This region comprises territory around Hamun Lake, wetlands in endorheic Sistan Basin on the Iran-Afghan border, and its primary watershed Helmand river in what is nowadays southwestern region of Afghanistan.