The articles addressed this some.

As I understand the area is unlikely to have any of the rock in which caves form as primary structures, such as by dissolution of bedrock minerals in waters, i.e., karst topography, or like lava tube caves. It is likely to have talus caves, which is consistent with those depressions in the hills that the locals call the Colebrook Dinosaur Tracks.

A talus cave is also consistent with the descriptions of smooth surfaces, boulders falling from the ceiling, and a lack of stalactites.