Our reporter Liao Ailing - When Yanqing County's Dazhuangke Township was cleaning up the environment on both sides of the Changchi Road, they dug out a huge stone pit 17.5 meters deep. Yesterday, I learned that geological experts have preliminarily identified the giant stone pit as likely being a geological wonder formed over a million years ago known as a "rock mortar," but this has not yet been officially confirmed.
The excavation unearthed more than 3000 cubic meters of soil. This giant stone pit is located under the Bailongtan Bridge at the intersection of Changchi Road and Lianhua Mountain Road. In the center of a huge granite block, it has an elliptical opening with smooth walls. They also dug out a cast-iron "Dragon King statue" and some remaining hand grenade shells from it. The Dragon King statue has been sent to the Yanqing cultural relics department for identification, while the hand grenade shells have been handed over to the township for safekeeping.
According to the on-site engineering staff, there was originally only a small opening of a few square meters here. While tidying up the environment on both sides of Changchi Road, the workers originally intended to clear the mud in the pit, but unexpectedly, the deeper they dug, the deeper it became. "The pit is straight up and down. At first, we were digging manually, but no matter how much we dug, we couldn't reach the bottom." Later, a small excavator was brought in, but its arm wasn't long enough, so a large excavator had to be called in. After continuous digging for a month, the true appearance of the giant stone pit gradually revealed itself. It resembles a round altar, entirely embedded in a huge granite rock, 20 meters wide, 18 meters long, and 17.5 meters deep. More than 3000 cubic meters of soil were excavated in total.
The appearance of the giant stone pit attracted the curiosity and attention of many people. Locals from nearby villages said that the giant pit is located within the Bailongtan (White Dragon Pool). The water in Bailongtan was still very deep in the 1980s, and no one had seen the giant pit. Later, as the water level decreased, and due to this year's drought, the pit is estimated to have finally become visible.
Yanqing once had glaciers over a kilometer thick
Regarding the cause of this giant stone pit, researcher Han Tonglin from the Institute of Geology, Chinese Academy of Geological Sciences, descended into the pit on August 17th to take photos and conduct surveys. He stated that it has been preliminarily determined that this large stone pit is scientifically named a "rock mortar" and may have formed during the glacial period two to three million years ago, when melting ice caused water to fall vertically and create the impact.
He introduced that in Beijing region, rock mortars two or three meters deep have been found in places like Wuling Mountain, Wangbaochuan Village in Changling Town, and Huairou Liumiao area, but such a deep rock mortar as found in Dazhuangke Township is the first of its kind. It can be considered "the largest among the well-preserved rock mortars discovered domestically thus far." He mentioned that the glacier that originally impacted it must have been at least a kilometer thick, indicating that two to three million years ago, the Yanqing region was once covered by glaciers over a kilometer thick.
Official investigations are ongoing
Currently, there is still no official explanation for the cause of the stone pit. The Yanqing cultural relics department has already taken samples from the stone pit for identification, and the Yanqing County Land and Resources Bureau's Department of Geological and Mineral Management has also dispatched survey personnel to the scene. The conclusion should be available soon.