The Tagant gives the surrounding administrative region its name, and it sets the terms for everything around it. Its slopes fall away into cliffs, and at the foot of those cliffs cluster the towns of the region: Tichit, Moudjéria, Rachid. The town of Tidjikdja sits up on the plateau itself. Read the rock closely and time stretches strangely. The Assaba Massif, a southward extension of the Tagant, preserves glacial formations from the Late Ordovician, some 440 million years ago, when this part of Africa lay near the South Pole under a continental ice sheet. The same ground that now bakes under the Saharan sun once ground beneath glaciers.

To the south, the plateau's escarpments drop toward the Aoukar, the dry bed of a former lake. The two landforms tell a single story when you put them side by side: the high stony Tagant and the low parched basin below it, the cliff and the dead sea it once overlooked. Along that boundary, ancient settlements and the famous ksar of Tichit grew up where the highland met the water that used to be there. The Tagant is not just scenery. It is the shelf on which one of West Africa's oldest cultural landscapes was built, the firm ground above a basin that has been drying for thousands of years.

The people on the plateau today are not the first. Beginning in the mid-seventeenth century, migrants moving down from the Adrar Plateau to the north pushed into the Tagant and displaced the population they found there, the Toucouleur. Those displaced communities resettled far to the south in Futa Toro, along the Senegal River, where their descendants live still. It is the desert's quiet, recurring history: a hard land changing hands, one group arriving as another is pushed out, the older claim surviving as memory and migration rather than as any line on the ground.

Return, finally, to the crocodiles, because they are the plateau's strangest truth. The Tartega gueltas are among the very few wetlands here, pockets of permanent water trapped in the rock. West African crocodiles were recorded in them as late as 1976, then declared gone in 1996, then confirmed alive again in 1998–1999, hanging on around Lake Gabou. They are living fragments of the Green Sahara, the era thousands of years ago when this desert ran with rivers and lakes. As the water shrank, most of that wet-country wildlife died out or moved on. A handful of crocodiles simply stayed, shrinking their world to a few stone pools and waiting out an entire climate.