Water and lava, the two characteristic features of Sant Joan les Fonts landscape, coexist in splendid harmony at Molí Fondo. Lava flowing thousands of years ago from Garrinada and Batet volcanoes cooled to form a basalt stone waterfall.

Molí Fondo is one of the few places in Europe where you can see three superimposed layers of lava, corresponding to three different historical periods (600.000, 150.000 and 120.000 years ago respectively). The third and most recent of the lava flows can be seen above Molí Fondo at the former basalt quarry of Boscarró.

This place is included in the three lava flows route.