Blue marls

Much of the Ódena basin is littered with characteristic geological formations made up of hillocks of bluish-grey earth that are strongly eroded and furrowed by deep ditches or gullies.

These bluish soils, known as marls, were formed on the seabed and are therefore rich in mollusc, echinoderm, coral and foraminifera fossils. They are part clay and part calcium carbonate and in some places can be up to 600 meters thick.

The dissolution of the carbonates releases the clay and facilitates erosion, forming the characteristic gullies. In this state, the marls are called "badlands", where, because of their aridity, no plants grow.

More information:

https://ca.wikipedia.org/wiki/Marga 
https://www.ub.edu/portal/web/ciencies-terra/margues-d-igualada 
https://naturalocal.net/ca/rutes-senderisme-catalunya/rutes-senderisme-barcelona/rutes-senderisme-seva/ruta-dels-rellotges-de-sol-de-seva/margues-blaves