A Paleozoic Intrusion
The story of the Stolby pillars begins deep underground during the Paleozoic Era. Recent studies indicate the rocks formed between 430 and 450 million years ago, during the Late Ordovician to Early Silurian periods. At this time, a mass of molten magma pushed its way upwards into overlying layers of Cambrian-period sedimentary rock from depths of 500 to 1,500 meters. This was not a volcanic eruption, but an intrusion—a body of magma that never reached the surface. Instead, it slowly cooled and solidified deep within the Earth's crust, forming what geologists call a pluton.
The rock is often called granite, but it is more accurately classified as syenite, an intrusive igneous rock high in potassium feldspar but with a very low quartz content. The slow cooling process, insulated by kilometers of rock, allowed large, well-defined crystals of minerals like orthoclase feldspar and hornblende to grow. This is what gives the rock its coarse-grained (phaneritic) texture and pinkish-red color. The entire formation, known as the Shumikhinskiy intrusive complex, has the shape of a stock—a cylindrical, drop-like body that extends deep into the crust.
Sculpted by Time and Weather
For millions of years, this massive body of syenite lay hidden. The land above it was part of an ancient, flattened plain called a peneplain. Tectonic uplift associated with the formation of the Eastern Sayan Mountains raised this entire region. As the land rose, the forces of erosion—wind, rain, and ice began to strip away the softer sedimentary rocks that surrounded and covered the hard, crystalline syenite.
As the syenite cooled and the immense pressure from the overlying rock was removed, a system of vertical and horizontal cracks, known as joints, formed throughout the massive. Water seeped into these cracks, freezing and thawing with the seasons. This process, called frost wedging, acted like a chisel, prying the rock apart along these pre-existing fractures. Selective weathering along the joints sculpted the rock into mattress-like blocks and the bizarre, pillar-like shapes seen today. The resulting pillars, or "stolby," are erosional remnants—the hard cores of the ancient magma intrusion left standing after the surrounding landscape weathered away. Today, there are more than 100 individual rock pillars, with some reaching heights of 90 to 100 meters.