This site is 180 km long and 20–25 km wide, and is located 3 km from Ranohira. It consists of a large sandstone massif, with a peculiar ruinlike aspect, that rises out of a plain. This chain of outcrops includes deeply eroded canyons, the most famous of which are Monkey Canyon and Rat Canyon. The hydrographic network is composed of clear, fast-flowing streams, which drain into the tributaries of the Menamaty in the east, and into those of the Mangoky and Malio in the west. There are also marshes, such as at Andranovorinkaolo, as well as lakes, such as the Golden Lake, whose flora includes Polygonum, Echinochloa, Panicum and Cyperus. Forest covers 10% of the park’s area, and comprises three types. The dense, dry deciduous forest, mainly composed of Commiphora and Dalbergia, is relatively degraded. Gallery forest is dominated by Eugenia, Tamarindus and Mangifera—one area of this type, Andranofotsy, in the north of the park, has an area of c.240 ha. Low- and mid-altitude, dense, humid evergreen forest occurs in the shelter of canyons and is composed of Voacanga, Nuxia, Weinmannia and Tambourissa. The understorey is composed of thick clumps of ferns Blechnum. The vegetation on open areas of bare rock includes species of Pachypodium, Kalanchoe, Senecio, Aloe, Helichrysum and Euphorbia. Wooded savanna covers 40% of the site’s area, and includes trees of Stereospermum, Albizia, Borassus, Pemphis and Dicoma. Open savanna, with or without scattered palms (of Bismarckia and Hyphaene) is more common.
See Box and Tables 2 and 3 for key species. Eighty-one species are known from the site, of which 27 are endemic to Madagascar. The range of Monticola bensoni is restricted to the Isalo–Zombitse Vohibasia region, including Analavelona (IBA MG066) and possibly the Mangoky canyons (MG063). It appears to have a rather patchy distribution within the park, being absent from large areas in the centre.