A geologist's primary method is to observe an outcrop and then a variety of contemporary environments looking for an analogous match. If there is no contemporary environment to use for comparison, geologists combine bits from different environments, extrapolate, and use them to interpret the outcrop. The reasoning process at the outcrop involves something more that mere mechanical matching of features. For example, although no one can know everything about the Grand Canyon, one person can know enough about the rock formations to be able to find water and the way out if left in an unknown side canyon. This sense of orientation allows the geologist to engage their imagination, to envision the outcrop.
Geologists interpret the hidden depths.
The geologist looks at a two-dimensional surface and sees three or four dimensions. Geologic vision is embodied knowledge, arrived at through walking the land, seeing the outcrop within its context of the landscape. Geologic insight is a kind of walking meditation.