Where do people perform an annual ritual, involving dance and masks made of mud, to honor their river god?

people perform an annual ritual, involving dance and masks made of mud, to honor their river god in Mali, West Africa
The people in this region believed that the river god is really important because it provide the source of living for their agricultural plants, so they worwhip it everyday.

Use the formula: (n-2)×180, where n is the number of sides(18-2)×180= 28800, now this is the full exterior angle of 18-gon so you divide it by 18.28800÷18=160