Volcanic detritus had been accumulated by volcanic activities of Mt. Nijo (Nara Prefecture, Osaka Prefecture) and later tuff appeared on the ground due to earth uplifting; since then the tuff has undergone weathering and erosion for 15 million years to become a crag at 150 meters in height having oddly-shaped rock outcrops.
二上山(奈良県・大阪府)の火山活動により火山岩屑が沈積し、その後の隆起によって凝灰岩が露出し、1500万年間の風化・浸食を経て奇岩群となった標高約150mの岩山。