Castildetierra

Castildetierra is the inverted-funnel landform that identifies the Bardenas Reales: a clay chimney protected on top by a layer of harder rock. It stands in the Bardena Blanca, next to the Cortinas ravine, at the start of the perimeter track, and the Comunidad de Bardenas itself describes it as the most photographed landmark in the park, receiving hundreds of visitors every day. It is the essential stop on any visit, however short.

How it formed

The Bardenas are a fill of clays, silts, gypsum and sandstones that was deposited in large lakes between 21 and 15 million years ago, when the Ebro basin was closed to the sea. Since the Ebro found its way to the Mediterranean, erosion has not stopped. Where a hard layer of sandstone, limestone or conglomerate protects the clays beneath, landforms and plateaus remain standing, such as Castildetierra, Pisquerra or the Rallón. According to the Comunidad, Castildetierra is the most extreme example of this phenomenon, and its researchers calculate that it formed within the last 10,000 years.

The clay is soft and every storm carries off a little. Because of this risk of collapse, the Comunidad announced as early as 2004 a wooden perimeter fence to limit access to its base, and in 2011 commissioned a full scan of the landform that would allow it to be rebuilt precisely if it falls. Wikipedia records estimates that, at the current rate of erosion, it could last about four decades.

How to see it

You can see it from the track and from the signposted walk along the Cortinas ravine, which starts from the same car park. Park in the marked space and approach on foot along the path: you may not climb it, go round it across country or touch it. Beside the landform there is a fixed stand for taking a phone photo with the best framing and QR codes with information in several languages about its geology.

The park opens to visits from 8:00 until one hour before dusk. In morning or afternoon light the rock takes on colour and the shadows pick out the relief; at midday in summer the light is flat and the heat strong. In the Bardenas the use of drones for recreational purposes is forbidden, here too.

Getting there

From Arguedas, take the NA-134 towards Tudela and, after a kilometre, past a petrol station, the paved lane on the left: at 5.9 km is the information centre and at 10.5 km Castildetierra, all on tarmac, so any car can get there. From here the loop along the perimeter track of the Bardena Blanca begins, which circles the military range and passes close to the Pisquerra and the Rallón.

With children and with a dog

It is a short, flat stop, perfect with small children: the path from the car park is brief and there is nothing to climb. Dogs may come, on a lead of 3 metres at most. There is no shade or fountains: bring water.