This geosite is located on the northern edge of the Geopark on the deep wedge of the River Ibor in the vicinity of where it meets the River Tajo. Easy access is afforded by the CC-19 road that links Bohonal de Ibor to Mesas de Ibor, just below the three bridges known as Puentes de las Veredas that were built at different historical periods to take advantage of the narrowness of the watercourse some 3 km from Bohonal.
The geosite lies some 300 metres downstream of the old transhumance bridge and is a good example of one of the phenomena caused by the fluvial erosion of the hard rock to be found in the riverbeds. This is that of “potholes”, a geological term that refers to large virtually spherical concavities caused by fluvial erosion which is favoured by the discontinuities of the riverbed and by the solid material that is dragged over rocky areas. Locally they are known as “pilones” or “pilancones”.
They form on riverbeds owing to the gyratory action of very hard boulders dragged by the current when these fall in small depressions or concavities at the bottom of the watercourse. Due to the movement of the waters, when these hard rocky fragments turn within the concavities the latter become rounded and at the same time their walls become wider and deeper to form the “potholes”. The hardness of the fragments needs to be equal to or greater than that of the rocks in which the concavity forms. At this geosite we are concerned with quartzite boulders transported by the River Ibor and the rocks where the cavities form, which are porphyric granites (granites with large crystals of orthose feldspar) that have been intensely fractured by orthogonal diaclases (horizontal and vertical fractures). The places where these fractures intersect may constitute the gaps that encourage the development of future “potholes”. This is therefore a good example of intensive fluvial erosion caused by whirlpools, but there is also a certain tectonic influence (with the presence of diaclases) in their morphology and distribution along the watercourse.
We can contemplate here one of the most spectacular sections of the valley of the River Ibor, a deep defile precisely where the “potholes” are to be found, excavated directly in the granitic rocks of the riverbed.
The middle course of the River Ibor reaches the potholes before it cuts down to meet the Tajo. From ancient times use has been made of this watercourse for the construction of various river mills; one of these is located here and both its structure and associated engineering elements can be seen: the waterwheel and the channel used to divert the water to the millstone. As for the landscape, the old transhumance bridge, potholes, mill, water, and vegetation are very pleasant aesthetically, especially in summer when one can relax and bathe here.
The river wedge has protected the riparian woodland that includes both young and adult specimens of alders, black poplars, and willows, which are accompanied on the hillside by Montpellier maples and hackberries together with other shrubs such as wild roses that also seek cool humid soils.
