The gap you walk into: reading a difeng

Chinese describes the karst of Wulong with a pair of words. A tiankeng is a collapse hollow, a hole you stand at the rim of and look down into; a difeng is a rift, a crack you descend into and walk along. The standard phrase for the landscape joins both, tiankeng and difeng, with natural bridges and caves, and calls the result three-dimensional karst. Longshui Gorge, Longshuixia, is the difeng of the Three Natural Bridges conservation area. It appears in the park's own list of features between the Yangshui River karst canyon and the two Shiyuan tiankengs, one of a series of named hollows, caves and hidden streams inside the 22 square kilometres.

The gorge belongs to the same water system as the bridges. The Yangshui River, a tributary of the Wu, is the stream that runs under Tianlong, Qinglong and Heilong, and a rift in the same limestone is what the same water opens when it follows a joint instead of cutting a span. Chongqing's geography makes the connection explicit: it names the Longshuixia Gap together with the Three Natural Bridges as what turned this part of the municipality into a tourist destination, and it describes karst as common across the area, with limestone caves and valleys in many places. A rift is one of the forms that karst takes, alongside the hollow, the cave and the bridge.

The district's other hollows offer the closest thing to an explanation. At Houping the Qingkou Tiankeng Scenic Area holds five tiankengs, and it is described as the only tiankeng group so far found in the world that was formed by surface water erosion; its core zone runs to 7,134 hectares and its buffer zone to 46,781. Surface water, in other words, is credited here with making holes as well as bridges, which is the argument a rift asks you to accept: that a stream working along a line of weakness in the limestone can, given time, remove more rock than it leaves standing.