Final answer:
Colors on a large-scale topographic map represent different geologic units and their contacts.
Step-by-step explanation:
On a standard large-scale topographic map, different colors are used to represent different features. The colors on the map usually represent geologic units, which are subdivided by time and rock types. For example, shades of yellow are used for Quaternary units and blues are used for Paleozoic units.
Between these colored units, lines designate different types of contacts, such as fault (solid line), intrusive contact (dashed line), or contact covered by unconsolidated rocks (dotted line). There is typically a legend on the map that identifies the colors and lines used.