3.2.3. Caves

The caves appear associated with karstic environment and have been formely studied [5].

### 3.2.4. Travertine Buildings

A good number of examples exist associated with active springs: Orbaneja del Castillo, Tubilla del Agua, Covalagua, Barriolucio, Hoyos del Tozo, Villaescobedo, Moradillo del Castillo, Revilla de Pomar, Rebolledillo de la Orden and Fuenteodra.

### 3.2.5. Peat Bogs

They appear restricted to specific examples in La Piedra, Urbel del Castillo, Humada, Fuencaliente de Puerta, Corralejo del Valdelucio.

### 3.2.6. Canyons and Sickles

Associated to the Ebro, Rudrón and Pisuerga valleys.
