Three Sisters, Blue Mountains, NSW, Australia. Fully customizable. The Three Sisters is a rock formation in the Blue Mountains of New South Wales, Australia. They are close to the town of Katoomba and are one of the Blue Mountains' best known sites, towering above the Jamison Valley. Their names are Meehni (922 m), Wimlah (918 m), and Gunnedoo (906 m). The Sisters were formed by erosion. The soft sandstone of the Blue Mountains is easily eroded over time by wind, rain and rivers, and the cliffs surrounding the Jamison Valley are being slowly broken up. Formations like the Three Sisters are created when water seeps into small cracks in the rock, gradually enlarging them over time to form large indentations. Eventually, the Sisters will be eroded away completely.