The surficial geologic map of the Eastern and Central United Statesdepicts the areal distribution of surficial geologic deposits and othermaterials that accumulated or formed during the past 2+ million years,the period that includes all activities of the human species. Thesematerials 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 oneway or another to these surface materials that are referred tocollectively by many geologists as regolith, the mantle of fragmentaland generally unconsolidated material that overlies the bedrockfoundation of the continent. The map is based on 31 published mapsin the U.S. Geological Survey's Quaternary Geologic Atlas of theUnited States map series (U.S. Geological Survey MiscellaneousInvestigations 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 beprinted as a conventional paper map at 1:2,500,000 scale.This map is not a map of soils as recognized and classified inagriculture. Rather, it is a generalized map of soils as recognizedin engineering geology, or of substrata or parent materials in whichagricultural, agronomic, or pedologic soils are formed. Where surficialdeposits or materials are thick, agricultural soils are developed onlyin the upper part of the engineering soils. Where they are very thin,agricultural soils are developed through the entire thickness of asurficial deposit or material.The surficial geologic map provides a broad overview of the arealdistribution of surficial deposits and materials. It identifies anddepicts more than 150 types of deposits and materials. In general,the map units are divided into two major categories, surface depositsand residual materials. Surface deposits are materials that accumulatedor were emplaced after component particles were transported by ice,water, wind, or gravity. The glacial sediments that cover the surfacein much of the northern United States east of the Rocky Mountains arein this category, as are the gravel, sand, silt, and clay that weredeposited in past and present streams, lakes, and oceans. In contrast,residual materials formed in place, without significant transport ofcomponent particles by ice, water, wind, or gravity. They are productsof modification or alteration of pre-existing surficial deposits,surficial materials, or bedrock. For example, intense weathering ofsolid rock, or even stream deposits, by chemical processes may producea residual surficial material that is greatly transformed from itsoriginal physical and chemical state.In recent years, surficial deposits and materials have become thefocus of much interest by scientists, environmentalists, governmentalagencies, and the general public. They are the foundations ofecosystems, the materials that support plant growth and animalhabitat, and the materials through which travels much of the waterrequired for our agriculture, our industry, and our general wellbeing. They also are materials that easily can become contaminatedby pesticides, fertilizers, and toxic wastes. In this context, thevalue of the surficial geologic map is evidentThe map and its digital database provide information about fourmajor aspects of the surficial materials, through description ofmore than 150 types of materials and depiction of their arealdistribution. 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 orwere emplaced or how long specific processes have been acting onthe materials), (3) properties (the chemical, physical, and mechanicalor engineering characteristics of the materials), and (4) thicknessor depth to underlying deposits or materials or to bedrock. Thisapproach 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 environmentalorganizations and consultants, to academic scientists and institutions,and to the layman who merely wishes to learn more about the materialsthat conceal the bedrock. The map can facilitate regional andnational overviews of (1) geologic hazards, including areas ofswelling clay and areas of landslide deposits and landslide-pronematerials, (2) natural resources, including aggregate for concreteand road building, peat, clay, and shallow sources for groundwater,and (3) areas of special environmental concern, including areas ofintense erosion and areas of potential contamination of soil andgroundwater.The map also includes lines depicting the maximum limits of glacialadvance during selected time periods.