Here the Ebro stops being a river and becomes a lake. Behind the great dams at Mequinenza and Riba-roja, the water backs up for kilometres into the dry hills of eastern Aragon, and locals call the reservoir the Mar de Aragón, the sea of Aragon. Val de Caballé is a gully in the hills south of the water, between Mequinenza, Nonaspe and Fabara, part of a scatter of prehistoric rock shelters in this corner where Aragon, Catalonia and the Matarranya meet.
The landscape is stark and beautiful in its own way: terraces of olives and almonds, wheat fields, low cliffs of pale sandstone, and the occasional ruined farmhouse. It feels remote even though it is not far from busier roads. Mequinenza has an extraordinary story. The old town sat at the confluence of the Ebro and the Segre and was largely flooded when the reservoir filled in the 1960s and 70s; residents were moved to a new town built nearby. There is a museum dedicated to the old village and another to the coal mines that once employed much of the population. The reservoir is now famous among anglers for its giant wels catfish, introduced decades ago, and you will see fishing camps along the shores.
Fabara, a few kilometres south, has a well-preserved Roman funerary monument, the mausoleum of Lucius Aemilius Lupus, a small temple-like tomb standing in a field. It is a lovely, slightly surreal stop.
The riding is mostly open and flowing. The roads that link Mequinenza, Fayón, Nonaspe and Caspe follow the contours of the hills and the reservoir, with long views and a mix of fast bends and tighter sections as they drop into side valleys. Traffic is light, though you will meet the odd truck heading to a farm or quarry. Wind can be strong and gusty, especially the cierzo from the northwest, and summer heat here is serious. Spring and autumn are ideal.
For fuel, Mequinenza and Caspe are the safe bets; smaller villages may not have pumps. Mequinenza has bars and restaurants, many catering to visiting anglers. Carry water, because between villages there is little shade and fewer people, and the hills can feel very empty in the heat of the afternoon.