A stone run, called also stone river is a rock landform, resulting from the erosion of particular rock varieties caused by freezing-thawing cycles taking place in per-glacial conditions during the last Ice Age. The actual formation of stone runs involved five processes: weathering, solifluction, frost heaving, frost sorting, and washing. The stone runs are essentially different from moraines, rock glaciers, and rock flows or other rock phenomena involving the actual flow of rock blocks under stress that is sufficient to break down the cement or to cause crushing of the angularities and points of the boulders. By contrast, the stone river boulders are fixed quite stably, providing for safer climbing and crossing of the run.
Stone river is a natural wonder and it can be found in Vitosha mountain. Also called Golden bridges are the most visited area of Vitosha mountain. Even before the Second World War, when there is no way from Sofia to this place, mountain lovers with backpacks had been coming in the weekends on the small paths of Knyazhevo, Boyana and Vladaya to enjoy the beautiful scenery. Today the Golden Bridges are reachable by road, which connects the capital with this natural wonder.
The natural wonder The Golden Bridges 1390 m above sea level is located in the middle of the Vladayska River, at the border between North (Kamendel) and North-Western (Selimishki) sections of Vitosha. Impressive are the huge oval stone blocks of syenite (moraines) along the wide riverbed. They completely cover the water stream, for the presence of which we can realize only by the muted rumble. Most of the moraines are covered with yellowish moss, which, in the sun, acquire a golden color. This is one of the explanations for the name – Golden bridges. Others associate the name with the presence of golden sand in the river, which is also a fact. The area also impresses with the huge spruce trees, the ancient beech and the beautiful birches.
The Golden Bridges is one of the most frequently used exit points to Black peak (Cherni Vrah).
There are two theories about the origin of the Golden bridges, The Stone river. The first: the sliding of the glaciers at the end of the quarter (the ice age). According to this theory, glacier origin have all stone rivers in other parts of the mountain. Depending on the other theory, they are a result of the blocked cracking of Vitosha monzonite (kind of a stone) with a subsequent spherical shaping because of erosion effect of the river and wind.