Cachoeira Ponte de Pedra

How did the Ponte de Pedra form?

1. 1

   The ancient basement (over 2.1 billion years)

   • More than 2.1 billion years ago the region's oldest rocks formed: the schists and gneisses of the Ticunzal Formation — whose type area is right here in Cavalcante.
   • Between 2.15 and 2.0 billion years ago, great masses of granite (Aurumina Suite) intruded those old rocks.
   • That granite-and-gneiss basement is what crops out today in the valley below the falls and around town.

   
2. 2

   A rift opens and fills with sand (~1.77 billion years)

   • Around 1.8–1.6 billion years ago the crust stretched and broke, opening a rift — a long, deep valley — with volcanoes active around 1.77 billion years ago.
   • Rivers, gravel fans and wind-blown dunes filled that valley with sand and pebbles: the sediments of the Arraias Formation, Araí Group.
   • That is the unit where the Geological Survey of Brazil's map places the Ponte de Pedra area — right at the edge where the rift cover meets the old basement.

   
3. 3

   Sand turns to hard rock

   • Buried under new layers of sediment, the rift sands were compacted and cemented into hard sandstone.
   • The final transformation into quartzite — quartz grains welded together, one of the most erosion-resistant rocks there is — probably came with the heat and squeeze of the continental collision in the next step.
   • Not every layer ended up equal: in the region, pure hard quartzites alternate with more micaceous, crumbly layers — a difference that will matter later.

   
4. 4

   Continents collide: folds and fractures (~600 million years)

   • About 600 million years ago, the continental collision that built the Brasília Belt folded and fractured the rocks across the whole region.
   • In Cavalcante those folds are giants — one is visible at the Mirante da Nova Aurora, near here.
   • The fractures opened back then became the preferred paths where water would go to work.

   
5. 5

   The plateau rises and the river plunges

   • Much later the region was uplifted and erosion stripped the softer layers, leaving hard quartzite holding up the highlands.
   • Around Ponte de Pedra, the São Domingos river drops nearly 500 metres from the plateau rim to the valley floor within a few kilometres (elevation-model estimate).
   • It is on that raised rim of hard quartzite that the river makes the great leap of the waterfall — 70 to 100 m depending on the source; further down, the valley already runs over the basement granites and gneisses.

   
6. 6

   And the arch? The classic stone-bridge process

   • We found no published geological study of this specific arch — the closest description, from a travel account, says it was “opened by the slow, patient work of the waters” of the river.
   • In stone bridges like this one, water tends to find its way through weaker layers or fractures beneath a hard quartzite bed, widening the passage little by little until the whole river flows underneath — leaving the resistant layer suspended as a bridge, here with a span of nearly 30 metres according to the local operator.
   • The rock is about 1.8 billion years old, but the bridge itself is a young, fleeting landform: like every natural bridge, one day it will thin out and collapse.

   

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