Geologists call this landform a glint: an escarpment where a sheet of sedimentary rock meets, and rides over, an eroded crystalline basement. The Ibiapaba is a cuesta - steep on one side, gently inclined on the other. Its east face drops sharply into Ceará. Its west side tilts away in a long, almost imperceptible ramp toward Piauí, so that a traveller crossing from that direction may reach the summit without ever feeling they climbed. The range measures roughly 200 kilometres north to south and 50 kilometres across, with most of the plateau surface between 700 and 850 metres and high points reaching around 954 metres. It runs from near the Atlantic coast in the north down to a junction with the Serra do Araripe, which forms Ceará's southern boundary. The Poti River cuts through it; the southern segment, between the Poti and the Araripe, carries its own name, Serra Grande.

The rock is old and the story it records is patient. These are the sandstones, conglomerates, shales and diamictites of the Serra Grande Group, laid down on the eastern edge of the Parnaíba Basin between roughly 458 and 419 million years ago - Ordovician into Devonian, a stretch of time when the land here lay near the South Pole and the first plants were only beginning to colonise dry ground. Everything the escarpment does today is downstream of that geology. Sandstone is porous, so the plateau stores water and releases it as springs along the cliff line. Sandstone is also hard, which is why the wall has not worn back into slope.

Northeast Brazil is dry. The Ibiapaba is the exception, and it manufactures its own exception. Moist air off the Atlantic runs west across the plain, hits the escarpment, is forced up, cools and unloads - orographic rainfall exceeding 2,000 millimetres a year on the eastern face, in a region where the surrounding sertão gets a fraction of that. The consequence is a biological island. Winter mornings on top run 13.5 to 15°C with fog in the valleys, cold enough to need a jacket at three degrees south of the equator. The vegetation is a collision zone: humid Atlantic-type forest on the wet slopes, cerrado on the drier tablelands, the palm stands of the Mata dos Cocais, caatinga at the base, and scattered Amazonian elements that reached here and stayed. Brazilians call such places brejos de altitude - highland marshes - and this is one of the largest.

The Tabajara called themselves Os Senhores da Serra, the lords of the range, and they had reason to. They had migrated here from the São Francisco River region before Europeans arrived, and they held the high ground - defensible, watered, and productive in a landscape where none of those things could be assumed. They were also already trading. French merchants were dealing for forest products on this coast before the Portuguese established themselves, and the Tabajara and neighbouring Tapuia groups negotiated with them directly. The Jesuits came later and came to stay. António Vieira, the most formidable preacher in the Portuguese empire, visited the range in 1660, and the mission of Ibiapaba was formally established on 15 August 1700, becoming a colonial centre in its own right. The names that survive on the plateau today - Viçosa do Ceará, Tianguá, Ubajara, São Benedito, Guaraciaba do Norte, Ibiapina - grew from that layered history rather than replacing it.

At the foot of the range near Ipu, water comes out of the rock at a place called the Bica do Ipu. Ceará has made it a literary shrine. José de Alencar's Iracema - the novel that gave Brazil one of its founding romantic myths, and Ceará one of its enduring self-images - is locally identified with this spring, and the scene of Iracema bathing there has been painted and reproduced ever since. José Maria de Medeiros put her on canvas in 1884, in a painting that won imperial recognition the same year. Whether Alencar had this particular bica in mind is a question Cearenses do not much enjoy being asked. The escarpment is the kind of landform that attracts stories, and it has collected them for as long as anyone has lived beneath it.