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Our transcription: To locate the geologic structures in an area like this, the geologist first looks for patterns in the distribution of rocks at the Earth's surface. Because soil and vegetation usually conceal most of the rock we need to see, this type of analysis can't be done from airplanes or satellite. Instead, geologists spend a great deal of time studying the rocks on the ground. Information about each individual rock exposure or outcrop is recorded and then plotted on a base map. Constructed outcrop by outcrop, this information eventually becomes a geologic map. The different colors show how rocks of different types and ages are distributed throughout the area. These rocks are described here in the map explanation. Faults are shown as dark lines, and special symbols indicate where rocks are tilted and folded.
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