Situated in the province of Fianarantsoa , the Isalo is an imposing mountain covering an area of 81 540ha spreading over nearly hundred kilometers south-northwise and culminating to an average altitude of 1000m . Isalo National Park includes the part of Isalo mountain northward the depression taking by RN7. Ranohira , the neighbouring main city of the park is situated on the RN7 : at 85 km from Ihosy and 243 km from Tuléar. Composed of continental sandstone dating back the jurassic the mountain presents in its south and east part a typical ruin shaped relief . There are deep canyons ( monkeys and rats Canyons ) of several kilometers long , 100 to 200 m of sheer . The north and west part appear in the form of great rocky barriers of 200 to 300 m high cut by narrow and deep gorges .

The climate is dry tropical type with annual precipitations of 850mm . from June to August : a marked dry season ; from October to March : rainy season , maximum of precipitation in November and December .
Monthly average temperatures comprised between 17 °C in June and 25°C in February .

The mountain vegetation undergoes an intense and alarming degradation caused by the almost yearly bush fires repeated action . The grassy areas represent at least 40% of the park surface, the forest covers only 10% . The most current species are : Uapaca bojeri , Uapacaceae , Asteropeia rhopaloides , Alberta orientalis ,Rubiaceae , Sarcolalaceae……..The canyons shelter forests in which predominate Apocynaceae , Sapindaceae , Leguminoceae…….The abundant rocky vegetation mainly marked by a kind of Pachypode is distributed on the totality of the park : pachypodium rosulatum , apocynaceae , a kind of Aloé : aloé isaloensis and a kind of euphorbe : euphorbia @@duvani.

Ten mammals among which the Propithecus verreauxi , the lemur fulvus , and the lemur catta . The tenrec ecaudatus , the cryptoprocta ferox ( fosa) . 55 species of birds among which the Benson rock blackbird , the Coracopsis nigra , the Milvus migrans , the Coua cristata , the Dicrirus forficatus (drongo ). Among the reptiles : the Chamaeleo lateralis , the Oplurus sp.