It is a protected nature area due to the existence of a peculiar karst complex, formed by dolines and blind valleys of major hydro-geological interest. It has three main chambers: the Sumidoiro del Fondadal, at a depth of 156 metres, Vistulaz Cave and the Vegalonga System, which, with a length of 5,900 metres, represents one of the largest underground complexes in the region.
In these mountain passes can be found grassland with buckthorn and low scrub vegetation, generally heather, gorse, holly, Genista occidentalis, hawthorn and blackthorn.
This Natural Monument forms part of the Caldoveiro Peak Protected Landscape.
