Aler

This mill is situated between Torres del Obispo and Aler and is in fact built closer to the former but still inside the latters territory. Torres del Obispo is perhaps not that easy to find because it's not on the regular tourist track. From Graus take the main road to the south and after a while turn left for Benabarre. You'll soon reach Torres del Obispo. Take left at the branch leading to the village center. Keep to this road and you'll soon leave TdO at the east side. This is the old road for Aler and Tremp. After less than 2 km there are some sharp bends where the road crosses the Barranco de Gasíño. A sand path will lead you down into the valley and to the molino.
The mill got water from the Bco de Gasíño.

Pictures: 20.VIII.2006; Map: Inst. Geográfico y Catastral, 1952

(1) Wheat mill (white arrow) and Oil mill.

The mills are situated at the base of two very big millponds. If each mill had his own pond, or if both ponds were shared, I couldn't make out.
The Barranco de Gasíño, by the look of it, probably more often than not doesn't carry any water. The dashed line on the old map is telling us this was also true back then. It was therefore important that the ponds could stock as much water as possible and that no precious water would be lost because the pond had reached maximum capacity. That explains the size.