The massif is a page torn from deep time. Its sandstone belongs to the Isalo Group, a formation up to 6,000 meters thick, laid down between the Triassic and early Jurassic periods - roughly 180 million years ago - by braided streams that wandered across an ancient landscape long before this was an island. Those vanished rivers dropped layer upon layer of coarse sand, which hardened into stone and then, over eons, surrendered to the patient knives of wind and rain. The result is a sculpture garden of domes, mesas, and dissected outcrops, part of the southern Morondava Basin. Stand among the ruiniforms at dawn and you are reading a story written by water that dried up before the first dinosaurs grew large.

Isalo looks parched, and much of it is - hot, dry, dominated by grasslands and the gnarled, fire-adapted tapia tree that grows nowhere but Madagascar's highlands. Yet the canyons hide a different world. Where springs surface, palms and humid forest cling to the walls, sheltering ring-tailed lemurs that pose on warm rock and Verreaux's sifakas that cross open ground in their famous sideways bounds. By night the red-tailed sportive lemur and the gray mouse lemur emerge. On the bare rock itself grow oddities like the elephant's foot, a swollen-stemmed Pachypodium, and aloes found only here. More than a hundred bird species have been recorded, among them Benson's rock thrush, a bird closely tied to these cliffs. Six lemur species share the massif's contradictory landscape of furnace-dry ridge and cool green ravine, while fourteen mammal species in all have been documented in the park.

Long before it was a park, this was the country of the Bara, a cattle-herding people whose lives turn around zebu, the humped cattle that are wealth, ritual, and identity across much of Madagascar. The massif holds their dead. Tucked into cliff faces and crevices are Bara burial sites, and older tombs of the Sakalava who came before - the rock serving as both fortress and sepulchre. To walk Isalo's canyons is to move through a landscape that is sacred as well as scenic, where the silence of the high stone carries weight. A guide drawn from the local community is required to enter, and the trails range from a few hours' walk to expeditions of a week or more.

Isalo was established as a national park in 1962 and has been managed by Madagascar National Parks since 1997, but protection has not settled its central tension. Across this part of Madagascar, herders burn the land to flush green grass for cattle, and illegal fires set inside the park are its chief threat - each one nibbling back the forest and pushing the grasslands wider. Many of the "natural" pseudo-steppes here are really the legacy of generations of burning, which prevents trees from returning. The park's celebrated natural swimming pools - cold canyon water gathered in stone basins, beloved by trekkers escaping the heat - depend on the very forests the fires erode. Isalo's drama is geological, but its future is a daily negotiation between cattle, fire, and the canyons' hidden green.