It only occurs at the NW coast, mainly at the Mandraki area and in the valley behind Paleokastro, at altitudes up to 80m. Conglomerate beds, 0.5-1.5m thick, alternate with sandstone – tuffitic beds, 0.3-0.6m thick with a characteristic near-shore crossbedding.

Sizes of pebbles vary between 0.5cm and 0.7m, with an average diameter of 10-15cm. Pebbles are abundant in the lower layers; these originate from submarine lavas, while in the upper layers, all products present in the nearby area are also found there. Fallout layers of the Nisyros Upper Pumice Unit are intercalated in the upper layers of the conglomerate; this fact demonstrates that the conglomerate outcrop area used to function as a topography lowest (mainly a coastal area) in the near past; and the area has been raised following the latest caldera collapse.