They are located near Las Peñas de Riglos some 45 km (28 mi) to the northwest of the city of Huesca.

[1] The Mallos were formed when eroded material washed down from the slopes of the Pyrenees and became cemented together by limestone.

Over time, this mixture became compacted into a large mass of conglomerate rock.

The more resistant rock remained, and became the formations known as the Mallos de Riglos.

[1] Because of their relatively vertical sides, the Mallos de Riglos are a popular destination for climbers.