The mouth, 5.5 x 4.5 metres, is divided in two by a fallen block. A rocky arch is found 2 metres from the floor and marks the true entrance of the main gallery. On the left begins a gallery of 4 x 2 x 1 metres structured on a group of joints oriented to the NE. On the right the main gallery begins and a little further to the right another gallery of short length.

The main gallery widens quickly (3 x 2 metres) and further on becomes a bedding plane (due to the rise of the floor by the sediments) that leads to the mouth of a shaft. The gallery continues 6 metres more on the other side of the mouth of the shaft, but becomes impenetrable. The shaft, 1.5 metres in diameter, descends with a slight inclination towards the N, 8 metres from where, below some blocks, one descends by a ramp 3 metres more. Above these large blocks extends towards the E a small room with large clastic materials on the floor, which ascends towards the SE and allows access to the entrance gallery.

The main gallery, with a total length of 25 metres, leads to the mouth of a shaft; the gallery continues 6 metres more on the other side of the mouth of the shaft, but becomes impenetrable. The shaft descends 8 metres from where, below some blocks, one descends by a ramp 3 metres more. Above these large blocks extends towards the E a small room that ascends towards the SE and allows access to the entrance gallery.

The entire floor of the main gallery (with a total length of 25 metres) is occupied by an important deposit of fluvial sediments (from which comes the name of the cavity), formed by flattened and large pebbles on the surface (up to 25 centimetres in diameter) that form a layer of 10 to 15 centimetres and, below, another thicker layer formed by also flat pebbles, of smaller size, mixed with smaller materials.