13. Quartzite Ridges in Southwestern Nigeria

Quartzitic ridges traverse a large part of southwestern Nigeria, extending through the Oyo, Osun and Ekiti and terminating in some parts of Kwara States. Quartzites are known for their toughness, low porosity and permeability, and hence, they typically support terrain elevations. Quartzite ridges are particularly conspicuous around Ibadan township, around Iseyin and at Olokemeji. Although they occur mainly as ridges and as lines of hills, bedrock outcrops are rare because the ridges are often covered by flaggy debris due to rock weathering. Quartzite ridges are the most impressive and notable landform units in the Ibadan region. The ridges have a general width-to-length ratio of up to 1:20 or more with slope angles ranging between 10 and 21°, generally trending in the NNW-SSE direction. Their original relief has been modified by human impact, both directly due to various constructions and indirectly, leading to gully erosion.