The phonolites intruded and punctured the Mesozoic sedimentary rocks and the Tertiary flood basalts some 19 to 11 million years ago.

[1][2] The formation occurs as plugs that have punctured the Tertiary flood basalts of the Ethiopian plateau, and form the highest peaks in their surrounding.

[4] They are also exposed in Addi Amyuq, some 3 kilometres north of Hagere Selam, on the northern slope of the ridge.

The morphology of the Addi Amyuq phonolite outcrop is similar to that of Gobo Dura where the Aksum obelisks were quarried.

Notably, they were used to carve the monolithic obelisks and other monumental stones during the Aksumite kingdom.