- Draw a profile (TECHNIQUE NUMBER 7) along your desired
line of cross-section with sufficient detail to recognize the topography, especially if it
is structurally and/or lithologically controlled.
- Mark the locations of field-mapped or inferred geological contacts
where they cross the line of section. For lithologically controlled terrain, the
main rule is that the contact between a resistant and nonresistant unit lies at the bottom
of a dip slope, but below the top (by the thickness of the resistant unit) of a scarp
slope.
- Show the dip of subsurface units as extrapolated from field measurements or inferred
from the dip of exposed dip slopes - vertical
exaggeration is usually NOT a good idea.
- Continue the units to a reasonable depth - not so little that reasonable extrapolation
is restricted, nor so great that a huge leap of faith is required. A couple of
kilometers (several thousand feet) is usually appropriate.
- Show the thickness of geologic units as CONSTANT within a restricted map area, as
defined from field mapping or published stratigraphic columns or inferred
from topography. Note that the WIDTH of mapped outcrop is only equal to the
unit THICKNESS if the unit is vertical!
- Folds and faults mapped or inferred at the surface are likely to persist
at shallow depths, although they do not have to occur directly under their surface
manifestation.
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Topographic Map