Geologic maps · structures
A geologic map is a 3-D story flattened onto paper. Learn to unflatten it.
Contours tell you the shape of the land. Strike and dip tell you which way the rock is leaning. Put them together and the map tells you what’s underground — folds, faults, and the order of everything. Push the same reading outward and it explains plate boundaries and the waves that travel through the Earth.
Every line joins points of equal elevation. Where they bunch, the ground is steep; where they V, there’s a valley — and the V always points upstream.
Read the map
Loading…
A tilted bed meets the horizontal in a line — that’s the strike. The dip is how steeply it tips, measured at right angles to strike. Play with it, then read the symbols.
Read the symbol
Loading…
Erosion slices the top off a fold and prints its guts on the map. Oldest rocks in the core means an anticline; youngest in the core means a syncline. Faults show themselves by cutting and offsetting beds.
Map pattern
Loading…
The rules that make a map readable — and the symbols you have to know cold.
The ones that turn up most on exams.