The geological outcrop of les Ribes Blaves are fault rocks (fault flour), from a Neogene fault, on which a small badland has developed due to the flattery It is located on a section of the B-120 road between Olesa de Montserrat and Viladecavalls. It is located within the municipality of Olesa de Montserrat and is a destination for many geologists due to its uniqueness. It is a slate outcrop with a turquoise hue due to the high pressures and temperatures it reached during its formation. It is internationally recognized for its exceptionality and is one of the most important geological points in Catalonia, as it explains a stage in the formation of the country's relief. It is cataloged in the inventory of areas of geological interest in Catalonia.

In the past it was an uncontrolled landfill, until in the nineties of the 20th century it was closed thanks to a joint action between the Mountain Center and Research Olesà and the University of Barcelona. In those years, an urbanization was also built in the vicinity, which required the construction of a road on top of this very important outcrop. The sum of these two facts led to a progressive deterioration of the outcrop. In 2015 a landslide damaged the road, it wasn't until 2019 that the Diputació de Barcelona and the town council of Olesa de Montserrat completed a new route away from the outcrop and built a car park and an avenue-mirador for pedestrians.

An outcrop of the same order can be found in the Roques Blaves of Esparreguera, on the edge of Colònia Sedó.