The rocks that form the Portofino Promontory belong to the limestone of Mt. Antola formation and to the conglomerate of Portofino.

The limestone of Mt. Antola, that settled on the bottom of an ancient ocean dating back to between 90 and 55 million years ago, are formed by limestone, sandy limestone, marl and shale alternations. There are fossil traces of Helminthoidea labirintica, made by marine organisms that moved on the ancient sea-beds in search of food.

Marly limestone is the predominant rock type, a sedimentary rock with different layer heights, from decimetres to metres, and different colours, from yellowish-grey to grey, because of the surface alteration.

The limestone of Mt.Antola formation has been subjected to great strains that have deformed and fractured the layers causing folding and faulting that are particularly evident and attractive below the San Rocco area.

The conglomerate of Portofino settled in a shallow marine environment after the previously mentioned formation (between 37 and 28 million years ago). They were part of a very ancient river mouth that, according to recent studies, was probably fed by materials eroded from a mountain belt extending in the Ligurian Sea between Genoa and Savona. The conglomerate of Portofino is a sedimentary rock that consists of coarse-grained clastic rock fragments, well-rounded pebbles, in a sandy limestone matrix consisting of smaller particles like sand successively cemented by limestone.

The conglomerate of Portofino is made of different kinds of variably sized clastic pebbles that have different compositions depending on the depth where they are found and are representative of:

-          sedimentary rocks (limestone, marly limestone, sandy limestone and sandstone) predominant in the lower Promontory, that were the top of the original mountain belt;

-          metamorphic basic rock, metamorphic jasper, marble and dolomite, that were the middle part;

-          quartzite, sandy quartzite, low metamorphic conglomerate, crystalline metamorphic rocks (mica-schist, quartzitic-schist, paragneiss and orthogneiss sometimes showing migmatitic texture) predominant in the upper Promontory; they are very ancient rocks and formed the basal complex of the mountain belt from which the conglomerate derives.