The basalt crag where the town is situated is over 50 m high and almost a kilometre long and is the direct result of the erosive action of the rivers Fluvià and Toronell on the remains of the lava flows from the volcanic eruptions which took place thousands of years ago.
The lava, once solidified, became basalt, a hard rock which takes on different forms, depending on the cooling, contraction and splitting processes of the lava. The cliff is the result of two lava flows; the first took place 217,000 years ago, and originated in the area of the village of Batet, and has formed slabs, the second, a more recent formation from the volcanoes of Begudà is 192,000 years old, and has formed into prismatic shapes.
