OsmarHenry · CC BY-SA 4.0Cerro Acahay (complejo alcalino anular)
A ring-shaped massif born from alkaline magma that rose and cooled underground about 126 million years ago.
What it is
Acahay is an annular complex: a set of igneous rocks intruded in the shape of a ring, which erosion left standing as a massif visible from far away. It belongs to the Sapucaí Alkaline Province and has been dated to the Early Cretaceous. Its rocks include essexitic gabbro, syenogabbro, alkali gabbro, syenodiorite and trachyandesite, typical of alkaline magmatism.
It is part of the alkaline magmatic episode of about 126 million years ago, which accounts for the largest number of alkaline outcrops in eastern Paraguay. The massif was declared the Macizo Acahay Natural Monument by Decree 13,682 of 1992, covering about 2,500 hectares according to a UNA study.
How to visit
It is reached from Route PY01 near Carapeguá, and the hill can even be seen from the Cerro Lambaré lookout. Sources give different heights (between 485 and 560 m), so do not treat that number as exact. Check access before you go.
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Researched and reviewed in September 2026 with 4 sources. A second reviewer checked dates, coordinates and lodging. Hours and prices may change.