The rock formations are made of beautiful gray and purple rhyolites. They are huge rocks of different shapes: prismatic, step-like and conical. Their height is 5 to 15 and more meters. In the nearby area there are many interesting plant species. Right behind the rock phenomenon, on top of its northern slopes, is the only habitat of the area for both alpine plants – cornel-tree (Cotoneaster intergerimus) and Snowy Mespilus (Amelanchier ovalis) of the Pink family. There, in the clefts of the rocks, is the second in the country habitat of the rare plant species -white campion (Silene lerchenfeldiana) of the Flowering Plants group. This is a plant that usually occurs over two thousand meters above sea level and Ustra Peak is 1015 m high. Other rare species for the Bulgaria flora were found as well as large deposits of the precious golden rod herb (Solidago virga aurea).