The Aja Mountains are to an extent made up of granite, whereas the Salma are made up of basalt.[1] The phrase "Hadn formation" was used by Chevremont (1982) to refer to volcanic rocks of the area of Ha'il, and was treated by Hadley and Schmidt (1980) as being part of a silicic and volcaniclastic sequence referred to as the "Shammar group", in a broader, regional context.[3]