Surficial deposits and materials in the eastern and central United States (east of 102 degrees west longitude)

The surficial geologic map of the Eastern and Central United States
depicts the areal distribution of surficial geologic deposits and other
materials that accumulated or formed during the past 2+ million years,
the period that includes all activities of the human species. These
materials are at the surface of the earth. They make up the "ground"
on which we walk, the "dirt" in which we dig foundations, and the “soil”
in which we grow crops. Most of our human activity is related in one
way or another to these surface materials that are referred to
collectively by many geologists as regolith, the mantle of fragmental
and generally unconsolidated material that overlies the bedrock
foundation of the continent. The map is based on 31 published maps
in the U.S. Geological Survey's Quaternary Geologic Atlas of the
United States map series (U.S. Geological Survey Miscellaneous
Investigations Series I-1420). It was compiled at 1:1,000,000 scale,
to be viewed as a digital map at 1:2,000,000 nominal scale and to be
printed as a conventional paper map at 1:2,500,000 scale.
This map is not a map of soils as recognized and classified in
agriculture. Rather, it is a generalized map of soils as recognized
in engineering geology, or of substrata or parent materials in which
agricultural, agronomic, or pedologic soils are formed. Where surficial
deposits or materials are thick, agricultural soils are developed only
in the upper part of the engineering soils. Where they are very thin,
agricultural soils are developed through the entire thickness of a
surficial deposit or material.
The surficial geologic map provides a broad overview of the areal
distribution of surficial deposits and materials. It identifies and
depicts more than 150 types of deposits and materials. In general,
the map units are divided into two major categories, surface deposits
and residual materials. Surface deposits are materials that accumulated
or were emplaced after component particles were transported by ice,
water, wind, or gravity. The glacial sediments that cover the surface
in much of the northern United States east of the Rocky Mountains are
in this category, as are the gravel, sand, silt, and clay that were
deposited in past and present streams, lakes, and oceans. In contrast,
residual materials formed in place, without significant transport of
component particles by ice, water, wind, or gravity. They are products
of modification or alteration of pre-existing surficial deposits,
surficial materials, or bedrock. For example, intense weathering of
solid rock, or even stream deposits, by chemical processes may produce
a residual surficial material that is greatly transformed from its
original physical and chemical state.
In recent years, surficial deposits and materials have become the
focus of much interest by scientists, environmentalists, governmental
agencies, and the general public. They are the foundations of
ecosystems, the materials that support plant growth and animal
habitat, and the materials through which travels much of the water
required for our agriculture, our industry, and our general well
being. They also are materials that easily can become contaminated
by pesticides, fertilizers, and toxic wastes. In this context, the
value of the surficial geologic map is evident
The map and its digital database provide information about four
major aspects of the surficial materials, through description of
more than 150 types of materials and depiction of their areal
distribution. The map unit descriptions provide information about
(1) genesis (processes of origin) or environments of deposition
(for example, deposits related to glaciation (glacial deposits),
flowing water (alluvial deposits), lakes (lacustrine deposits),
wind (eolian deposits), or gravity (mass-movement deposits)),
(2) age (for example, how long ago the deposits accumulated or
were emplaced or how long specific processes have been acting on
the materials), (3) properties (the chemical, physical, and mechanical
or engineering characteristics of the materials), and (4) thickness
or depth to underlying deposits or materials or to bedrock. This
approach provides information appropriate for a broad user base.
The map is useful to national, state, and other governmental agencies,
to engineering and construction companies, to environmental
organizations and consultants, to academic scientists and institutions,
and to the layman who merely wishes to learn more about the materials
that conceal the bedrock. The map can facilitate regional and
national overviews of (1) geologic hazards, including areas of
swelling clay and areas of landslide deposits and landslide-prone
materials, (2) natural resources, including aggregate for concrete
and road building, peat, clay, and shallow sources for groundwater,
and (3) areas of special environmental concern, including areas of
intense erosion and areas of potential contamination of soil and
groundwater.
The map also includes lines depicting the maximum limits of glacial
advance during selected time periods.