Cappadocia is dominated by Mt. Erciyes and Mt. Hasan, volcanic mountains that erupted a long time ago and covered the area with volcanic ash. The ash solidified to form the soft tufa that composes the surface strata here. Gorges and valleys have been carved out by the process of erosion. The "fairy chimney", the signature of the region, is formed by resilient stones, protecting the column of softer material beneath it while the surrounding tufa is removed.