Trail of La Chorrera

The track that brings you here is a drove road running alongside the Chorrera stream itself, a brook that dries up in summer and on whose banks tall poplars rise. It runs between fenced sheep estates to the picnic area next to the car park. There we leave the car or the bike and begin the path.

The path is narrow and you have to walk in single file; it is the tidiest way to make sure the first person collects all the cobwebs. Signs guide us all along the route, which consists of following the path for a little more than a kilometre. It has earth sections, rocky areas of slates and sandstones and a few wooden walkways. In the damper places you need to walk with a little care so as not to slip, but never with difficulty.

The first stretch is Mediterranean woodland: holm oaks, Portuguese oaks and their replacement scrub, with rockroses and spurge flax. On the slopes around the valley holm oak woods, rockrose thickets, broom thickets and different kinds of heather dominate.

The site covers 38 hectares bordering Cabañeros National Park: the fences that mark its limit are at the top of the waterfall. For its Mediterranean woodland, its gallery forest and its geological interest, the regional government of Castilla-La Mancha declared it a Protected Landscape.

La Chorrera has great geological interest. We walk over an ancient seabed, with Lower Palaeozoic rocks more than 500 million years old, and in them you can see ripple marks, lamination, foliation and faults. The route goes from the oldest rocks, the Pusa Slates, to the youngest, the Azorejo Sandstones and the Intermediate Beds¹.

It was a shallow sea, but with different zones. Where the water was shallower, near the coast, sands were deposited, which are now sandstones and quartzites; further out and deeper, silts and clays, which are now slates. The variations are due to the rising and falling of sea level, the transgressions and regressions. Walking towards the waterfall we see how that sea gradually became shallower.

The first outcrop is of Pusa Slates, from the Lower Cambrian. Unlike the sandstones, which are made of quartz, the slates are made of clay minerals. Here they appear with intercalated sandstone layers and two structures can be told apart. The bedding is that of the original sediments, layers from half a centimetre to a metre thick that rivers carried from the erosion of ancient reliefs to the marine shelf. The foliation is an arrangement in sheets: under the pressure of the Variscan Orogeny, at the end of the Palaeozoic, the minerals grew and reoriented until they all lay parallel, and the layers were folded until they stood vertical.

In the sandier levels you can see ripple marks, the marks left by marine currents as they dragged sediment. If they are asymmetrical, they show the direction and sense of the current; if they are symmetrical, a back-and-forth movement, like that of the waves.

Rocks from a sea more than 500 million years old.

Further on we pass from the slates to the Azorejo Sandstones. They are from the same period, but younger, and that is why they lie on top. Between the two there is a transition zone; when the sandstones already dominate, we are at the contact. More sand means that the sea was shallower and the currents stronger. Among the sandstones finer rocks also appear, such as silty sandstones or sandy slates, from moments or places with weaker currents.

Then we come across a rocky outcrop divided in two, one on each side of the path, as if we were crossing the threshold of a door. It is a layer of quartzite, a rock much more resistant to erosion than the sandstones around it: its quartz grains hardly change.

If we look closely, the two blocks of the gate are displaced from each other. A fault runs between them, and its movement has slid the layers. On the wall of the upper block, the one higher on the slope, you can see a fault breccia: crushed rock with angular quartzite fragments, formed by the collision of the blocks, as in the quartzite towers of the Boquerón del Estena. There are also striations, lines on the rock that mark the direction of the friction. Here they are horizontal, so the blocks moved horizontally².

As we advance we gradually enter the riverside wood, or gallery forest. It has Atlantic features, a legacy of the glaciations: that flora has survived sheltered by the waterfall and its humidity³. There are hollies, birches, willows, ferns, butcher's-broom and wild roses, and on the rocks grow foxgloves (Digitalis spp.), pinks (Dianthus lusitanus) and stonecrops (Sedum spp.). Mosses are abundant.

Just before reaching the waterfall there is a spring. Very close is the first contact between sandstones and quartzites, without big changes in relief because the rocks on both sides are alike. The clue is a level of conglomerates, coarse sands with small quartzite pebbles, which almost always appears between these two formations.

Where the change shows best is at La Chorrera itself, a 15-metre waterfall in a valley running north–south. A sudden change in relief is almost always a change of rock: here the stream passes from sandstones to harder quartzites, both of the Intermediate Beds. The sandstones have quite a lot of quartz, but do not reach the resistance of the quartzites, which are almost all quartz. Millions of years of erosion did the rest.

One question remains. If erosion has been working for so long, the relief should already be smooth, and in fact it once was. Today's valleys, cliffs and waterfalls are due to the faults, which raised the land in the middle of the Cenozoic, between 45 and 20 million years ago. The new watercourses cut into the rocks again and, in passing, made this waterfall⁴.

A 15-metre waterfall where sandstone gives way to quartzite.

We go back along the same path. It has the advantage that we already know it and the drawback that the rocks are just as slippery.

It is worth looking at the ground and at the sky. In autumn, mushrooms and fungi come up among the leaf litter. Above, vultures usually pass, and on the cliffs and the stream you can see rock-nesting birds, those that breed on rocks, such as the Crag Martin, and others tied to water: the White-throated Dipper, swallows, wagtails and the Common Kingfisher. More about the birds of the rivers of Cabañeros.

Among the species of most interest at La Chorrera are the birch (Betula pendula subsp. fontqueri var. parvibracteata), the holly (Ilex aquifolium), the willows (Salix salviifolia and Salix atrocinerea), the Montpellier maple (Acer monspessulanum), cross-leaved heath (Erica tetralix), Portuguese heath (Erica lusitanica), the ferns (Osmunda regalis, Blechnum spicant, Athyrium filix-femina and Dryopteris affinis), butcher's-broom (Ruscus aculeatus), wild roses (Rosa sp.), orchids (Cephalanthera longifolia, Dactylorhiza maculata and Orchis spp.), honeysuckle (Lonicera periclymenum subsp. hispanica) and the sedge Carex elata subsp. reuteriana, which grows in tussocks.