The base of the Topo complex originated in numerous shield volcanoes, erupting from primordial fissural faults that ran along a northwest to southeast and east-southeast to west-northwest alignment.

[1] These structures are only observed in the curvature of the higher turf cones, as far as 700 metres (2,300 ft) above sea level.

[1][2][3] The island of São Jorge had its initial formation from the rising of magma along these fractures through the Earth's crust, resulting in effusive volcanism from the area east of Ribeira Seca until Topo (from which it got its name).

[1] But, continuous erosion, from coastal action, humidity and rainfall, wind and thermal amplitudes, resulted in an interior relief forming a more gently appearing landscape, in comparison to the western areas of Ribeira Seca.

[1] The volcanic complex occupies the eastern part of the island and consists of basalt lavas, hawaiite and mugearite (aa) lavas, from explosive pyroclastic rocks and cinder cones originating from Strombolian eruptions.