The Tharthar depression was formed during the Holocene age, mainly by karstification, due to dissolving of gypsum rocks of the Fatha (nearby area) Formation. Tharthar covers roughly , flows from the central and eastern parts of the Sinjar Mountains and adjacent hills, with a floor of -3 m, above the sea level. The maximum length and width of the depression are 120 and 48 km, respectively. The eastern rim of the depression is higher than the western one, the heights of both rims are and , respectively.