b. Examine the source materials to determine their accuracy and reliability.
c. Determine the types of rock present in the area from the assembled source material or through ground
d. Record estimated or observed structural and engineering characteristics of the various rock types and any
unconsolidated material that may be present, such as sand or gravel.
e. Rate both the structural and engineering characteristics of each unit. A rating of "A" should be assigned
only where characteristics are of the highest quality, a rating of "B" should be assigned where the quality is
somewhat lower, and a rating of "C" should be assigned when most of the characteristics are poor.
f. Delineate the boundaries and label the polygons of each unit, using a topographic map or remotely sensed
image as a base.
g. Transfer the boundaries and labels to a transparent overlay material that has been registered to the
topographic map or the remotely sensed image.
h. Add a legend to the margin of the overlay.
i. Edit the overlay to ensure neatness, accuracy, and completeness.
2. Example of a Geologic Overlay. Figure 1-19 is an example of a geologic overlay that was prepared by
following the steps previously outlined. Figure 1-19(cont.), page 1-36, shows the supporting data tables for one
of the units depicted in the sample overlay.