The complex contains a semicircular western ridge and lava domes.
The volcano has erupted rhyolites and dacites and some andesitic lava flows on a ridge above Baeza.
At least two eruptions of Pumayacu occurred during the Holocene; one dated 4400 years ago and another's lapilli deposits overlie a cultural horizon 2000 years old.
[1] Older eruptions have been dated at 1.15 ± 0.07 Ma and are of high-potassium types.
They compromise typical arc-derived lavas with fractional crystallization and other differentiation processes.