Lesson l/Learning Event 3
patterns, can provide valuable clues as to the relative nature of rocks, degree of weathering, soils, and
drainage. When used with other sources of information, interpretations can often be made that could not
be made from any single source.
Soils Maps. These maps are best suited for the location of potential pit sites. They present information
on the distribution of soil units which are classified by thickness, texture, engineering properties, or
other characteristics. They often provide data which reflect local drainage, ground water, or geologic
conditions. It is best to use soil data with available geologic information to help clarify the details of
subsurface conditions. Soil maps and reports are available through the Soil Conservation Service of the
United States Department of Agriculture and from similar agencies in many foreign nations.
Aerial Photographs. You may request aerial photographs to supplement incomplete or dated maps or to
substitute where maps are unavailable. Current aerial photos present an up-to-date picture of the land.
Vegetation, roads, streams, rock outcroppings, excavations, and many other features can be clearly
identified. An experienced interpreter can determine much information on rock types, soil, drainage,
and ground water conditions from aerial photos alone. But the photos are most reliable when used with
other sources of information or with ground investigation. Often aerial photos will be the only source of
information available in the field.
Generally, an aerial photo shows dark tones where there is a high moisture content in the soils and/or
heavy vegetative ground cover. Very dark tones may be dense forests or ponded water bodies. High
topographic position and barren ground shows as light tones. A mottled tone is typically associated with
limestone formations. A conspicuous banded pattern is a key to identifying exposed, interbedded
limestone and shale. Limestone shows as a light tone while shale shows as dark.
Intelligence Reports. Strategic and tactical intelligence reports can be useful sources of information.
Intelligence reports published by the Defense Intelligence Agency and the Central Intelligence Agency
include information on soil types, rock formations. and existing pits, quarries, and mines. These are
important sources for long-range planning. Strategic engineer analyses prepared by the Office, Chief of
Engineers, and the engineer section of specified unit commands are also good sources.
Tactical intelligence reports compiled at all command levels are excellent sources of information on
terrain and potential pit or quarry sites. After-action reports from units in the field, especially engineer
units, may also identify potential sources of construction material.
Local Inhabitants. Residents may provide much useful data on local geology and engineering
problems. Surveyors, contractors, engineers, farmers,