Topographically the deserts consist of alternating tablelands and massifs dissected by river valleys and canyons. Iturup consists of volcanic massifs and mountain ridges. Major geographic features include plains, plateaus and massifs. Steep pitons were succeeded by wooded massifs. Outcrops of granite tend to form tors and rounded massifs. Geological substrate is varied and includes the tsingy limestone massifs. Harzburgite may also be found in some Alpine peridotite massifs that consist mostly of lherzolite. Erosion of mountains massifs can create a pattern of equally high summits called summit accordance. It is a complex of high flat-topped mountain massifs divided by deep and wide canyons. These are isolated mountains or massifs. Wolf populations in Mali have been documented in arid Sahelian massifs. The region is characterised by accidented relief of massifs and mountains. Bioko is rugged, made up of two volcanic massifs. Instead, they form aggregations called patches, banks, bioherms, massifs, thickets or groves. The erosion has left remaining massifs of Caledonian rocks and windows of Precambrian rock.