The geological origin of the Harrat is a volcanic field formed by tectonic activity from the Oligocene through to the Quaternary period. It is the largest of several volcanic field on the Arabian Plate, containing more than 800 volcanic cones and around 140 dikes and ring dikes. The Jabal al-Druze, al-Safa and Dirat al-Tulul volcanic fields, among others, form the northern and Syrian part of the harrat; Al-Harrah is in the southern, Saudi Arabian, third of the field.