It is a sandstone landscape that has been dissected by wind and water erosion into rocky outcrops, plateaus, extensive plains and up to 200 m (660 ft) deep canyons.

[citation needed] The group is up to 6,000m thick, of Triassic to early Jurassic origin and made up of coarse-grained sandstone deposited by braided streams.

[5] A 2024 archaeological study of man-made rock-cut niches at a site called Teniky found them to be from the tenth to twelfth centuries CE, of possibly Zoroastrian provenance.

The park includes several natural swimming pools which are popular among tourists, and are excellent sites to see the Benson's Rock Thrush.

Over 100 species of bird have been found here,[17] including Benson's rock thrush (Monticola sharpei bensoni), the knob-billed duck (Sarkidiornis melanotos) and the Madagascar ibis (Lophotibis cristata).

[15] Twenty four amphibians and 47 reptiles have been documented in Isalo National Park, including a number of new “candidate” species.

[15] Botanical inventory of the Isalo region began with collections by Perrier de la Bâthie in 1910.

Several of these have been documented in the Isalo area,[10] including the type specimen and only known location for the narrowly endemic Isalonactis madagascariensis.

[19] The sclerophyllous (hard-leafed, drought adapted) woodlands of Isalo are dominated by the endemic tree tapia (Uapaca bojeri).

Some of these moist habitats however are now dominated by introduced species such as Melia azedarach, Mangifera indica or Eugenia sp.

Although vegetation is sparse, a number of endemic species are found in these habitats, including Xerophyta sp., elephant's foot (Pachypodium rosulatum var.

[19] Secondary shrub communities are found where the slopes of the Isalo Massif contact fields or pastures.

The most common species in these communities are listed as:[19] Mimosa latispinosa, Vangueria madagascariensis, Maesa lanceolata, Aphloia theaeformis, Crotalaria sp., and Tamarindus indica.

Native grasslands, probably once restricted to small patches, are thought to have expanded as a result of intensive burning, primarily to facilitate cattle grazing.