Samburu National Reserve lies north of the Uaso Nyiro, which forms the southern boundary of the Reserve. The topography rises gently form the river, with altitude increasing in a northerly direction. Samburu's geological features are dominated by ancient basement complex rocks hornblende gneisses and schisis, and banded biotite gneisses, outcrops of which from the isolated steep-sided hills, or inselbergs, such as Koitogor, Lolkoitoi and Lowa Mara. The soils are generally sandy or gravelly, derived from weathering of the basement rocks.