Karst region around Sivas, Hafik and Zara

Tertiary Era limestone extends underground between Sivas in the west and the regional center of Imranli in the east and a karst landscape dominates the upper Kizilirmak for a distance of 100km/62mi, extending 10-20km/6-12mi on both sides. The river has cut its way through the layers of gypsum to create this wide valley and for over 100km/62mi it flows mainly through red sandstone, gypsum and marl. There are many tributaries which give the water a permanently dull red color, hence the name Kizilirmak ("red river"). The high levels of sodium and potassium compounds also give the water a bitter taste. The higher gypsum plateaux at about 1,550-1,650m/5,000-5,500ft are riddled with a dense network of dolines. The slopes close to the river abound with 50-100m/165ft-325ft wide and 30m/100ft deep funnels and craters with swallow holes (ponors). Uvalas and tiny poljes with shallow lakes and marshes have been created from larger dolines merging together.