At the northern end of the Gulf of Gaeta, it is about 5 kilometres (3.1 mi) long by 1.5 kilometres (0.93 mi) wide at the base, running from east to west and surrounded by the sea on all sides except the north.

The entire coast of Lazio, on which the mountain and the marsh are located, was a chain of barrier islands that was formed on a horst and made part of the mainland by sedimentation of the intervening graben.

The mountain is composed mostly of marl and sandstone from the Paleogene and of limestone from the lower Early Jurassic.

In 1939, the skull of a Neanderthal man was found in the Guattari Cave by a team led by Alberto Carlo Blanc.

The Minister of Culture in Italy declared the site to be one of the most significant in the world regarding the Neanderthal period.