These ancient remains date from the Quaternary Period, some 2.5 million years ago. Several hundred million years earlier, however, the Beijing area was engulfed several times by the sea. The Western Hills, for example, came into being a mere 100 million years ago as the result of a movement of the earth’s crust. During this period, the Beijing area was covered with a mantle of ice and snow and populated by hairy rhinoceros, mammoths caves bears and other creatures now long extinct. Due to climatic variations, the glaciers alternately advanced and receded, carting with them large quantities of rock which continually scraped away at the earth’s surface, leaving traces of their movements in the brown base rock.

The Beijing Municipal Cultural Relics Administration has set up railings to protect these vestiges. When visiting this site, it is likely that at first one will be unable to discern anything at all. But by using the method developed by the geologist Li Siguang, one will be able to discover the traces of the glacial period: Sprinkle water onto the brown base rock along the mountain slope, and the marks of the glacial abrasion will gradually come into view.