Prepared in cooperation with the Commonwealth of Massachusetts 

Massachusetts Geological Survey and Office of Geographic Information (MassGIS), 

Information Technology Division 

Surficial Geologic Map of the Mount Grace-Ashburnham-MonsonWebster 24-Quadrangle Area in Central Massachusetts 

Compiled by Janet R. Stone 

Open-File Report 2006–1260–I 

U.S. Department of the Interior 

U.S. Geological Survey 
 

 

Cover figure: Quabbin Reservoir serves as water supply for the city of Boston, and is shown here (in blue) superimposed 

on part of the 1908 Ware 30-minute topographic quadrangle map. Constructed between 1933 and 1939 by impounding 

three branches of the Swift River with two dams, the reservoir inundated significant areas of four towns—Dana, Enfield, 

Greenwich, and Prescott, and parts of several others. Wide areas of glacial meltwater deposits now lie below water level in
 

the valley; the surfaces of these deposits rise to the north by about 5 feet per mile (mostly due to tilting caused by glacial
 

rebound) and emerge above water level in the northern part of the reservoir. Lower photograph shows bedrock, locally
 

mantled by till, sloping toward the water’s edge in the southern part of the reservoir near the former site of Greenwich 

Village; stratified deposits are completely submerged. Upper photograph shows islands of glacial stratified deposits at the
 

north end of the reservoir, viewed from the overlook at New Salem. Photographs by J.R. Stone and M.L. DiGiacomoCohen, U.S. Geological Survey.
 

U.S. Department of the Interior 

SALLY JEWELL, Secretary 

U.S. Geological Survey 

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia: 2013 

For product and ordering information:
 

World Wide Web: http://www.usgs.gov/pubprod 

Telephone: 1–888–ASK–USGS 

For more information on the USGS—the Federal source for science about the Earth,
 

its natural and living resources, natural hazards, and the environment:
 

World Wide Web: http://www.usgs.gov 

Telephone: 1–888–ASK–USGS
 

Suggested citation: 

Stone, J.R., comp., 2013, Surficial geologic map of the Mount Grace-Ashburnham-Monson-Webster 24-quadrangle area in 

central Massachusetts: U.S. Geological Survey Open-File Report 2006–1260–I.
 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply
 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
 

ii 
Contents 

Introduction .................................................................................................................................................................... 1
 

Surficial Materials in Massachusetts .............................................................................................................................. 2
 

Glacial till deposits ..................................................................................................................................................... 2
 

Glacial stratified deposits ........................................................................................................................................... 3
 

Postglacial deposits ................................................................................................................................................... 5
 

Description of Map Units ................................................................................................................................................ 5
 

Map Compilation ............................................................................................................................................................ 8 

References Cited ..........................................................................................................................................................11
 

Appendix: Sources of Data by 7.5-Minute Quadrangle .................................................................................................14
 

Figures 

1. Map showing general distribution of glacial and postglacial deposits in Massachusetts and map area of this report 2
 

2. Block diagram illustrating the typical areal and vertical distribution of glacial and postglacial deposits overlying 

bedrock............................................................................................................................................................. 4
 

3. Grain-size classification used in this report. ............................................................................................................... 6
 

4. Index map showing 7.5-minute, 1:24,000-scale quadrangles in this compilation ....................................................... 9
 

5. Index map showing compilation areas in Massachusetts ........................................................................................ 10
 

iii 
 

 

 

 

Conversion Factors 

Multiply By To obtain 

Length 

inch (in.) 2.54 centimeter (cm) 

inch (in.) 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

mile, nautical (nmi) 1.852 kilometer (km) 

yard (yd) 0.9144 meter (m) 

centimeter (cm) 0.3937 inch (in.) 

millimeter (mm) 0.03937 inch (in.) 

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi) 

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

Area 

square mile (mi2) 2.590 square kilometer (km2) 

square kilometer (km2

) 0.3861 square mile (mi2) 

iv 
 

Surficial Geologic Map of the Mount GraceAshburnham-Monson-Webster 24-Quadrangle Area in 

Central Massachusetts 

Compiled by Janet R. Stone 

Introduction 

The surficial geologic map layer shows the distribution of nonlithified earth materials at 

land surface in an area of 24 7.5-minute quadrangles (1,238 mi2 total) in central Massachusetts (fig. 

1). Across Massachusetts, these materials range from a few feet to more than 500 ft in thickness. 

They overlie bedrock, which crops out in upland hills and as resistant ledges in valley areas. The 

geologic map differentiates surficial materials of Quaternary age on the basis of their lithologic 

characteristics (such as grain size and sedimentary structures), constructional geomorphic features, 

stratigraphic relationships, and age. Surficial materials also are known in engineering 

classifications as unconsolidated soils, which include coarse-grained soils, fine-grained soils, and 

organic fine-grained soils. Surficial materials underlie and are the parent materials of modern 

pedogenic soils, which have developed in them at the land surface. Surficial earth materials 

significantly affect human use of the land, and an accurate description of their distribution is 

particularly important for assessing water resources, construction-aggregate resources, and earthsurface hazards, and for making land-use decisions. 

The mapped distribution of surficial materials that lie between the land surface and the 

bedrock surface is based on detailed geologic mapping of 7.5-minute topographic quadrangles, 

produced as part of an earlier (1938–1982) cooperative statewide mapping program between the 

U.S. Geological Survey (USGS) and the Massachusetts Department of Public Works (now 

Massachusetts Department of Transportation) (Page, 1967; Stone, 1982). Each published geologic 

map presents a detailed description of local geologic map units, the genesis of the deposits, and age 

correlations among units. Previously unpublished field compilation maps exist on paper or mylar 

sheets and these have been digitally rendered for the present map compilation. Regional summaries 

based on the Massachusetts surficial geologic mapping studies discuss the ages of multiple 

glaciations, the nature of glaciofluvial, glaciolacustrine, and glaciomarine deposits, and the 

processes of ice advance and retreat across Massachusetts (Koteff and Pessl, 1981; papers in 

Larson and Stone, 1982; Oldale and Barlow, 1986; Stone and Borns, 1986; Warren and Stone, 

1986). 

This compilation of surficial geologic materials is an interim product that defines the areas 

of exposed bedrock and the boundaries between glacial till, glacial stratified deposits, and 

overlying postglacial deposits. This work is part of a comprehensive study to produce a statewide 

digital map of the surficial geology at a 1:24,000-scale level of accuracy. This surficial geologic 

map layer covering 24 quadrangles revises previous digital surficial geologic maps (Stone and 

others, 1993; MassGIS, 1999) that were compiled on base maps at regional scales of 1:125,000 and 

1:250,000. The purpose of this study is to provide fundamental geologic data for the evaluation of 

natural resources, hazards, and land information within the Commonwealth of Massachusetts. 

1
 
 

Figure 1. General distribution of glacial and postglacial deposits in Massachusetts (Stone and others, 1993; 

MassGIS, 1999) and 1:24,000-scale quadrangles covered by this report. 

Surficial Materials in Massachusetts 

Most of the surficial materials in Massachusetts are deposits of the last two continental ice 

sheets that covered all of New England in the latter part of the Pleistocene ice age (Schafer and 

Hartshorn, 1965; Oldale and others, 1982; Stone and Borns, 1986). The glacial deposits are divided 

into two broad categories, glacial till and glacial stratified deposits. Till, the most widespread 

glacial deposit, was laid down directly by glacier ice. Glacial stratified deposits are concentrated in 

valleys and lowland areas and were laid down by glacial meltwater in streams, lakes, and the sea in 

front of the retreating ice margin during the last deglaciation. Postglacial sediments, primarily 

floodplain alluvium and swamp deposits, make up a lesser proportion of the unconsolidated 

materials. 

Glacial till deposits consist of nonsorted, generally nonstratified mixtures of mineral and 

rock particles ranging in grain size from clay to large boulders. The matrix of most tills is 

composed dominantly of fine sand and silt. Boulders, within and on the surface of tills, range from 

sparse to abundant. Some tills contain lenses of sorted sand and gravel, and less commonly, masses 

of laminated fine-grained sediments. The color and lithologic characteristics of till deposits vary 

2
 
across Massachusetts but generally reflect the composition of the local underlying and northerly 

adjacent bedrock, from which the till was derived. Till blankets the bedrock surface in variable 

thickness, ranging from a few inches to more than 200 ft, and commonly underlies stratified 

meltwater deposits. Tills deposited during the last two glaciations occur in superposition within 

Massachusetts (Koteff, 1966; Newton, 1978; Weddle and others, 1989). The upper till was 

deposited during the last (late Wisconsinan) glaciation; it is the most extensive till and commonly is 

observed in surface exposures, especially in areas where till thickness is less than 10 to 15 ft (thintill unit on the map). The lower till ("old" till) was deposited during an earlier glaciation (probably 

Illinoian). The lower till has a more limited distribution; it is principally a subsurface deposit that 

constitutes the bulk of material in drumlins and other hills, where till thickness is greater than 15 ft. 

The distribution of lower till is shown primarily by the thick-till unit on the map. The lower till 

generally is overlain by a thin mantle of upper till in these areas. In all exposures showing the 

superposed two tills, the base of the upper till truncates the weathered surface of the lower till. The 

lower part of the upper till commonly displays a zone of shearing, dislocation, and brecciation in 

which clasts of lower till were mixed and incorporated into the upper till during the last glaciation. 

End moraine deposits are composed predominantly of bouldery ablation till but also locally 

may include sorted sediments. These deposits were laid down by glacial-melting processes along 

active ice margins during retreat of the last (late Wisconsinan) ice sheet. Extensive end moraines on 

Nantucket and Martha’s Vineyard (fig. 1) are related to the terminal position of the lateWisconsinan ice sheet, and the end moraines on Cape Cod are associated with recessional positions 

of the last ice sheet. Less extensive end moraines occur locally elsewhere in southeastern 

Massachusetts, in the Boston area, and in the Gloucester-Rockport area of northeastern 

Massachusetts. 

Glacial stratified deposits consist of layers of well-sorted to poorly sorted gravel, sand, 

silt, and clay laid down by flowing meltwater in glacial streams, lakes, and marine embayments that 

occupied the valleys and lowlands of Massachusetts during retreat of the last ice sheet. Textural 

variations within the meltwater deposits occur both areally and vertically because meltwater-flow 

regimes were different in glaciofluvial (stream), glaciodeltaic (where a stream entered a lake or the 

sea), glaciolacustrine (lake bottom), and glaciomarine (marine bottom) depositional environments. 

Grain-size variations also resulted from meltwater deposition in positions either proximal to, or 

distal from, the retreating glacier margin, which was the principal sediment source. A common 

depositional setting contained a proximal, ice-marginal meltwater stream in which horizontally 

bedded glaciofluvial gravel and (or) sand and gravel were laid down; farther down valley, the 

stream entered a glacial lake where glaciodeltaic sediments were deposited, consisting of 

horizontally layered sand and gravel delta-topset beds overlying inclined layers of sand in deltaforeset beds. Farther out in the glacial lake, very fine sand, silt, and clay settled out on the lake 

bottom in flat-lying, thinly bedded glaciolacustrine layers. Thick sequences having these textural 

variations commonly are present in the vertical section of meltwater deposits across the State 

(Stone, J.R., and others, 1992). Most of the meltwater sediments in Massachusetts were deposited 

in or graded to large and small glacial lakes. These large and small lakes formed in north-sloping 

valleys and basins where they were dammed by the ice margin (ice-dammed lakes) and in southsloping valleys and basins where they were dammed by slightly earlier deltaic sediments 

(sediment-dammed lakes). The largest glacial lake in Massachusetts was an extensive sedimentdammed lake (glacial Lake Hitchcock), which occupied the Connecticut Valley lowland at altitudes 

below 365 ft during the retreat of the last ice sheet. Lake Hitchcock was dammed behind a mass of 

3
 
earlier deltaic sediments in the Cromwell-Rocky Hill area of central Connecticut, and the lake 

lengthened northward into northern Vermont and New Hampshire as the ice sheet retreated. 

Detailed geologic maps can show meltwater sedimentary units within each glacial lake or 

valley outwash system (Jahns, 1941, 1953; Koteff, 1966). These units, known as morphosequences 

(Koteff, 1974; Koteff and Pessl, 1981), are the smallest mappable stratigraphic units depictable on 

detailed geologic maps. Morphosequences are bodies of stratified meltwater sediments that are 

contained in a continuum of landforms, grading from ice-contact forms (eskers, kames) to non-icecontact forms (flat valley terraces, delta plains) that were deposited simultaneously at and beyond 

the margin of the ice sheet, and were graded to a specific base level. Each morphosequence consists 

of a proximal part (head) deposited within or near the ice margin and a distal part deposited farther 

away from the ice margin. Both grain size and ice-melt collapse deformation of beds decrease from 

the proximal to the distal part of each morphosequence. The head of each morphosequence is either 

ice marginal (ice contact) or near ice marginal. The surface altitude of fluvial sediments in each 

morphosequence was controlled by a specific base level, either a glacial-lake or marine water plane 

or a valley knickpoint. Few morphosequences extend distally more than 6 miles, and most are less 

than a mile in length. In any one basin, individual morphosequences were deposited sequentially as 

the ice margin retreated systematically northward. Consequently, in many places the distal, finergrained facies of a younger morphosequence stratigraphically overlies the proximal, coarse-grained 

facies of a preceding morphosequence. 

Figure 2 shows an example of the variability of sediment types in the subsurface of glacial 

stratified deposits. The figure shows schematically the relationship between coarse-grained deltaic 

deposits (sand and gravel and sand) and extensive fine-grained lake (or marine) deposits (fine sand, 

silt, and clay) in the subsurface. Such coarse- and fine-grained units are common in most of the 

valleys and lowlands of Massachusetts (Langer, 1979; Stone and others, 1979; Stone, J.R., and 

others, 1992; Stone and others, 2005). On these interim maps, coarse-grained and fine-grained 

textural variations within glacial stratified deposits are shown only where they occur at land 

surface. Subsurface textural variations are not shown. 

Figure 2. Block diagram illustrating the typical areal and vertical distribution of glacial and postglacial 

deposits overlying bedrock (modified from Stone, J.R., and others, 1992). 

4
 
The areal distribution of till and stratified deposits is related to the physiography of the State 

(fig. 1). The thickness of these materials varies considerably within these regions because of such 

factors as the high relief of the bedrock surface, changing environments of deposition during 

deglaciation, and various effects of postglacial erosion and removal of glacial sediments. In 

highland areas, notably in the western and central regions, till is the major surficial material, and is 

present as a discontinuous mantle of variable thickness over the bedrock surface. Till is thickest in 

drumlins (reportedly as much as 230 ft thick) and on the northwest slopes of most bedrock hills. 

Glacial meltwater deposits that average 50 ft in thickness (Stone and others, 1993) overlie the till in 

small upland valleys and north-sloping basins between bedrock hills. Glacial stratified deposits are 

the predominant surficial materials in the Connecticut River valley, the northeastern and 

southeastern lowlands, and on Cape Cod and the islands. These deposits generally overlie till; 

however, well logs indicate that in some places till is not present and the stratified deposits lie 

directly on bedrock. On Cape Cod and the islands, in the southeastern lowland, and in parts of the 

Connecticut River valley, these deposits completely cover the till-draped bedrock surface. 

Postglacial deposits locally overlie the glacial deposits throughout the State. Alluvium 

underlies the floodplains of most streams and rivers. Swamps occur in low-lying, poorly drained 

areas in upland and lowland settings, but swamp deposits are shown only where they are estimated 

to be at least 3 ft thick. Salt-marsh and estuarine deposits are present mainly along the tidal portions 

of streams and rivers entering the offshore areas. Beach and dune deposits occur along the 

shoreline. 

Description of Map Units 

Postglacial Deposits 

Artificial fill—Earth materials and manmade materials that have been artificially 

emplaced, primarily in highway and railroad embankments and in dams; may also 

include landfills, urban-development areas, and filled coastal wetlands 

Floodplain alluvium—Sand, gravel, silt, and some organic material, stratified and 

well sorted to poorly sorted, beneath the floodplains of modern streams. The texture 

of alluvium commonly varies over short distances both laterally and vertically, and 

generally is similar to the texture of adjacent glacial deposits. Along smaller 

streams, alluvium is commonly less than 5 ft thick. The most extensive deposits of 

alluvium in the map area are along the Millers, Swift, Ware, and Quaboag Rivers. 

Alluvium typically overlies thicker glacial stratified deposits 

Alluvial-fan deposits—Generally coarse gravel and sand deposits on steep slopes 

where high-gradient streams entered lower gradient valleys. Some alluvial fans in 

this area were graded to lowering levels of glacial lakes. Some fans continue to form 

today 

5
 
 

Swamp deposits—Organic muck and peat that contain minor amounts of sand, silt, 

and clay, stratified and poorly sorted, in kettle depressions or poorly drained areas. 

Swamp deposits are shown only where they are estimated to be at least 3 ft thick. 

Most swamp deposits are less than 10 ft thick. Swamp deposits overlie glacial 

deposits or bedrock. They locally overlie glacial till even where they occur within 

thin glacial meltwater deposits 

Glacial Stratified Deposits 

Sorted and stratified sediments composed of gravel, sand, silt, and clay (as defined in 

particle-size diagram, fig. 3) deposited in layers by glacial meltwater. These sediments occur as 

four basic textural units—gravel deposits, sand and gravel deposits, sand deposits, and fine 

deposits. On this interim surficial geologic map layer, gravel, sand and gravel, and sand deposits 

are not differentiated and are shown as Coarse Deposits where they occur at land surface. Fine 

Deposits also are shown where they occur at land surface. Textural changes occur both areally and 

vertically (fig. 2); however, subsurface textural variations are not shown on this interim map. 

PARTICLE DIAMETER 

10 2.5 .16 

256 64 4 

.08 

2 

.04 .02 .01 

1 .5 .25 

.005 .0025 .00015 inches 

.125 .063 .004 mm 

Boulders Cobbles Pebbles Granules 

Very 

coarse 

sand 

Coarse 

sand 

Medium 

sand 

Fine 

sand 

Very fine 

sand Silt Clay 

GRAVEL PARTICLES SAND PARTICLES FINE PARTICLES 

Figure 3. Grain-size classification used in this report, modified from Wentworth (1922). 

Coarse deposits include Gravel deposits composed of at least 50 percent gravel-size 

clasts; cobbles and boulders predominate; minor amounts of sand occur within 

gravel beds, and sand comprises few separate layers. Gravel layers generally are 

poorly sorted, and bedding commonly is distorted and faulted due to 

postdepositional collapse related to melting of ice. Sand and gravel deposits occur 

as mixtures of gravel and sand within individual layers and as layers of sand 

alternating with layers of gravel. Sand and gravel layers generally range from 25 to 

50 percent gravel particles and from 50 to 75 percent sand particles. Layers are well 

to poorly sorted; bedding may be distorted and faulted due to postdepositional 

collapse. Sand deposits are composed mainly of very coarse to fine sand, commonly 

in well-sorted layers. Coarser layers may contain up to 25 percent gravel particles, 

generally granules and pebbles; finer layers may contain some very fine sand, silt, 

and clay 

6
 
Fine deposits include very fine sand, silt, and clay that occur as well-sorted, thin 

layers of alternating silt and clay (varves), or as thicker layers of very fine sand and 

silt. Very fine sand commonly occurs at the surface and grades downward into 

rhythmically bedded silt and clay varves 

Glacial Till Deposits 

End moraine deposits—Composed predominantly of boulders and ablation-facies 

sandy upper till; lenses of stratified sand and gravel occur locally within the till. 

Surface boulders on end moraine deposits are generally more numerous than on 

adjacent till surfaces; dense concentrations of boulders are present in some places. 

Deposits occur as freestanding hummocky landforms, commonly in ridges. Only 

two small end moraine deposits are present in this compilation area, in the village of 

Hardwick in the Ware quadrangle 

Thin till—Nonsorted, nonstratified matrix of sand, some silt, and little clay 

containing scattered pebble, cobble, and boulder clasts; large surface boulders are 

common; mapped where till is generally less than 10 to 15 ft thick including areas of 

shallow bedrock. Predominantly consists of upper till of the last glaciation; loose to 

moderately compact, generally sandy, commonly stony. Two facies are present in 

some places: a looser, coarser grained ablation facies, melted out from supraglacial 

position; and an underlying more compact, finer grained lodgement facies deposited 

subglacially. In general, both ablation and lodgement facies of upper till derived 

from fine-grained bedrock are finer grained, more compact, less stony and have 

fewer surface boulders than upper till derived from coarse-grained crystalline rocks. 

Across Massachusetts, fine-grained bedrock sources include the red Mesozoic 

sedimentary rocks of the Connecticut River lowland, marble in the western river 

valleys, and fine-grained schists in upland areas 

Thick till—Nonsorted, nonstratified matrix of sand, some silt, and little clay 

containing scattered pebbles, cobbles, and boulders in the shallow subsurface; at 

greater depths consists of compact, nonsorted matrix of silt, very fine sand, and 

some clay containing scattered small gravel clasts. Mapped in areas where till is 

greater than 10 to 15 ft thick, chiefly in drumlin landforms in which till thickness 

commonly exceeds 100 ft (maximum recorded thickness is 230 ft). Although upper 

till is the surface deposit, the lower till constitutes the bulk of the material in these 

areas. Lower till is moderately to very compact and is commonly finer grained and 

less stony than upper till. An oxidized zone, the lower part of a soil profile formed 

during a period of interglacial weathering, is generally present in the upper part of 

the lower till. This zone commonly shows closely spaced joints that are stained with 

iron and manganese oxides 

7
 
Bedrock Areas 

Bedrock outcrops and areas of abundant outcrop or shallow bedrock—Solid 

color shows extent of individual bedrock outcrops; horizontal-line pattern indicates 

areas of shallow bedrock or areas where small outcrops are too numerous to map 

individually; in areas of shallow bedrock, surficial materials are less than 5 to 10 ft 

thick. These units are not mapped consistently among all quadrangles; see Appendix 

for level of bedrock outcrop mapping in each quadrangle 

Map Compilation 

This compilation is the eighth in a series of interim products and shows surficial geology in 

an area of 24 7.5-minute quadrangles in central Massachusetts. The quadrangles are Mount Grace, 

Royalston, Winchendon, Ashburnham, Orange, Athol, Templeton, Gardner, Quabbin Reservoir, 

Petersham, Barre, Wachusett Mountain, Winsor Dam, Ware, North Brookfield, Paxton, Palmer, 

Warren, East Brookfield, Leicester, Monson, Wales, Southbridge, and Webster (fig. 4; fig. 5, area 

I). Figure 5 shows all of the compilation areas for surficial geology in Massachusetts. The surficial 

geologic maps produced to date are areas A–G and area I. 

The surficial geologic map layer was compiled in several steps: 

1) Paper copies of the published surficial geologic maps for 9 quadrangles were scanned and 

georeferenced by MassGIS; 

2) The Office of the Massachusetts State Geologist (now the Massachusetts Geological 

Survey) vectorized the georeferenced images in order to digitally retain the original 

linework of the published maps (Mabee and others, 2004); 

3) Digital geologic map units were compiled and grouped into basic units in three shapefile 

layers: Postglacial deposits including artificial fill, floodplain alluvium, alluvial-fan 

deposits, and swamp deposits; glacial stratified deposits including coarse-grained and 

fine-grained deposits; and glacial till and bedrock including thin till, thick till (drumlins), 

outcrops and areas of shallow bedrock. The distribution of glacial stratified deposits 

beneath adjacent overlying postglacial deposits and water bodies was inferred by the 

compilers; 

4) The same basic units as those listed in step 3 above were compiled and digitized for 15 

unpublished quadrangles from scanned field maps by USGS personnel; 

5) The 24 individual quadrangle maps were joined and edge-matched in order to form a 

seamless digital geologic map layer. Discrepancies along quadrangle boundaries were 

resolved, and thick-till areas and shallow bedrock areas were added by the compilers in 

quadrangles where these units had not been previously mapped. 

8
 
Figure 4. The 24 USGS 7.5-minute, 1:24,000-scale quadrangles in this compilation. Sheet numbers refer to 

Adobe PDF map files of individual quadrangles. 

9 
All geologic mapping was completed at 1:24,000 scale (several quadrangles were 

previously published at 1:31,680 scale). The 1:24,000-scale, 10-ft contour interval topographic base 

maps (1954–1972 editions) used for this mapping effort are included as part of the digital data 

package in the 24k_basemaps folder. The GIS folder included with this report contains three 

ArcGIS shapefiles, which show the distribution of geologic units that cover the entire map area, 

and are intended for use at quadrangle scale. The shapefiles can be clipped by quadrangle or by 

town boundary. Unlike the units in conventional geologic maps, the digitally defined map units are 

arranged in layers according to superposition. The shapefile for till and bedrock is the bottom layer, 

which is overlain by the succeeding stratified deposits shapefile layer; these materials are shown 

everywhere they occur, including beneath postglacial deposits such as swamp deposits, and also 

beneath water bodies. The shapefile for postglacial deposits should be placed on top because these 

materials overlie the other two layers. Instructions for using the digital files are included in the 

README file and metadata. 

In addition to the seamless digital layers that cover the entire compilation area, Adobe PDF 

map files of the surficial geology layers shown with 1:24,000-scale topographic base map images 

have been generated for each quadrangle (see Sheets 1–24, indexed on figure 4). 

Figure 5. Compilation areas in Massachusetts. Letters represent sections of Open-File Report 2006–1260. 

Sections published to date are available online at http://pubs.usgs.gov/of/2006/1260/. 

10
 
References Cited 

Barosh, P.J., 1973, Preliminary surficial geologic map of the Webster quadrangle, Massachusetts 

and Connecticut: U.S. Geological Survey Open-File Report 73–19, 3 sheets, scale 1:24,000. 

Barosh, P.J., 2009, Bedrock geologic map of the Webster quadrangle, Worcester County, 

Massachusetts and Windham County, Connecticut: Office of the Massachusetts State Geologist 

Open-File Report 09-02, scale 1:24,000, 1 sheet and digital product (Adobe PDF and ESRI 

ArcGIS database). 

Barosh, P.J., and Johnson, C.K., 1976, Reconnaissance bedrock geologic map of the Leicester 

quadrangle, Massachusetts: U.S. Geological Survey Open-File Report 76–814, 9 p., 1 map sheet, 

scale 1:24,000. 

Eschman, D.F., 1966, Surficial geology of the Athol quadrangle, Worcester and Franklin Counties, 

Massachusetts: U.S. Geological Survey Bulletin 1163–C, scale 1:24,000. 

Field, M.T., 1976, Preliminary bedrock geologic map of the Ware area, central Massachusetts: U.S. 

Geological Survey Open-File Report 76–708, 3 p., 2 map sheets, scale 1:24,000. 

Hadley, J.B., 1949, Surficial geology of the Mount Grace quadrangle, Massachusetts: U.S. 

Geological Survey Geologic Quadrangle Map GQ–4, scale 1:31,680. 

Jahns, R.H., 1941, Outwash chronology in northeastern Massachusetts [abs.]: Geological Society of 

America Bulletin, v. 52, no. 12, pt. 2, p. 1910. 

Jahns, R.H., 1953, Surficial geology of the Ayer quadrangle, Massachusetts: U.S. Geological 

Survey Geologic Quadrangle Map GQ–21, scale 1:31,680. 

Koteff, Carl, 1966, Surficial geologic map of the Clinton quadrangle, Worcester County, 

Massachusetts: U.S. Geological Survey Geologic Quadrangle Map GQ–567, scale 1:24,000. 

Koteff, Carl, 1974, The morphologic sequence concept and deglaciation of southern New England, 

in Coates, D.R., ed., Glacial geomorphology: Binghamton, N.Y., State University of New York, 

Annual Geomorphology Symposia Series, Proceedings, v. 5, p. 121–144. 

Koteff, Carl, and Pessl, Fred, Jr., 1981, Systematic ice retreat in New England: U.S. Geological 

Survey Professional Paper 1179, 20 p. 

Langer, W.H., 1979, Map showing distribution and thickness of the principal fine-grained deposits, 

Connecticut Valley urban area, central New England: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1074–C, 2 sheets, scale 1:125,000. 

Larson, G.J., and Stone, B.D., eds., 1982, Late Wisconsinan glaciation of New England: Dubuque, 

Iowa, Kendall/Hunt, 252 p. 

Mabee, S.B., Stone, B.D., and Stone, J.R., 2004, Precise conversion of paper geologic maps to 

value-added digital products; the Massachusetts method for surficial geology: Geological Society 

of America Abstracts with Programs, v. 36, no. 2, p. 78. 

MassGIS (Massachusetts Office of Geographic Information), 1999, Surficial geology (1:250,000), 

October 1999 [statewide data layer]: Vector digital data available at 

http://www.mass.gov/mgis/sg.htm 

Moore, G.E., Jr., 1978, Preliminary bedrock, surficial, and structural data maps of the Southbridge 

quadrangle, Massachusetts and Connecticut: U.S. Geological Survey Open-File Report 78–220, 

16 p., 4 map sheets, scale 1:24,000. 

Mulholland, J.W., 1975, Surficial geology of the Ware quadrangle, Worcester and Hampshire 

Counties, Massachusetts: Amherst, Mass., University of Massachusetts, unpublished Ph.D. 

dissertation, 291 p. [Dissertation Abstracts International, v. 36, no. 2, p. 620 B, 1975] 

Newton, R.M., 1978, Stratigraphy and structure of some New England tills: Amherst, Mass., 

University of Massachusetts, unpublished Ph.D. dissertation, 256 p. 

11
 
Oldale, R.N., and Barlow, R.A., 1986, Geologic map of Cape Cod and the Islands, Massachusetts: 

U.S. Geological Survey Miscellaneous Investigations Series Map I–1763, 1 sheet, scale 

1:100,000. 

Oldale, R.N., Valentine, P.C., Cronin, T.M., Spiker, E.C., Blackwelder, B.W., Belknap, D.F., 

Wehmiller, J.F., and Szabo, B.J., 1982, Stratigraphy, structure, absolute age, and paleontology of 

the upper Pleistocene deposits at Sankaty Head, Nantucket Island, Massachusetts: Geology, v. 

10, no. 5, p. 246–252. 

Page, L.R., 1967, The role of the United States Geological Survey in Massachusetts, in Farquhar, 

O.C., ed., Economic geology in Massachusetts: Amherst, Mass., University of Massachusetts, p. 

9–28. 

Peper, J.D., 1977, Surficial geologic map of the Monson quadrangle, Massachusetts and 

Connecticut: U.S. Geological Survey Geologic Quadrangle Map GQ–1429, scale 1:24,000. 

Peper, J.D., 1978, Surficial geologic map of the Palmer quadrangle, south-central Massachusetts: 

U.S. Geological Survey Geologic Quadrangle Map GQ–1465, scale 1:24,000. 

Peterson, V.L., 1984, The structure and stratigraphy of the bedrock in the Ashburnham-Ashby area, 

north-central Massachusetts: University of Massachusetts Department of Geosciences, 

Contribution 47, 182 p. and map, scale 1:24,000. 

Pomeroy, J.S., 1977, Surficial geologic map of the Warren quadrangle, Worcester, Hampden, and 

Hampshire Counties, Massachusetts: U.S. Geological Survey Geologic Quadrangle Map GQ– 

1357, scale 1:24,000. 

Pomeroy, J.S., 1975, Preliminary surficial geologic map of the East Brookfield quadrangle, 

Worcester County, Massachusetts: U.S. Geological Survey Open-File Report 75–531, 7 p., 2 map 

sheets, scale 1:24,000. 

Robinson, Peter, 2008, Bedrock geologic map and cross sections of the Orange area, 

Massachusetts, consisting of the Orange 7.5-minute quadrangle, the western part of the Athol 

7.5-minute quadrangle and the eastern part of the Millers Falls 7.5-minute quadrangle: Office of 

the Massachusetts State Geologist Open-File Report 08-04, scale 1:24,000, 5 sheets and digital 

product (Adobe PDF files). 

Seiders, V.M., 1976, Bedrock geologic map of the Wales quadrangle, Massachusetts and 

Connecticut: U.S. Geological Survey Geologic Quadrangle Map GQ–1320, scale 1:24,000. 

Schafer, J.P., and Hartshorn, J.H., 1965, The Quaternary of New England, in Wright, H.E., Jr., and 

Frey, D.G., eds., The Quaternary of the United States: Princeton, N.J., Princeton University 

Press, p. 113–128. 

Springston, George, 1990, Stratigraphy and structural geology of the Royalston-Richmond area, 

Massachusetts-New Hampshire: Amherst, Mass., University of Massachusetts, M.S. thesis. 

Stone, B.D., Lapham, W.L., and Larsen, F.D., 1992, Glaciation of the Worcester plateau, WareBarre area, and evidence for the succeeding late Woodfordian periglacial climate, Trip C-7 in 

Robinson, Peter, and Brady, J.B., eds., Guidebook for field trips in the Connecticut Valley region 

of Massachusetts and adjacent states: New England Intercollegiate Geological Conference, 84th 

Annual Meeting, p. 467–487. 

Stone, B.D., 1982, The Massachusetts State surficial geologic map, in Farquhar, O.C., ed., 

Geotechnology in Massachusetts: Boston, University of Massachusetts, p. 11–28. 

Stone, B.D., Beinikis, A.I., and Foster, Richard, 1993, Sand and gravel resources of Massachusetts: 

Boston, Mass., New England Governors' Conference, 2 map sheets, scale 1:250,000. 

Stone, B.D., and Borns, H.W., Jr., 1986, Pleistocene glacial and interglacial stratigraphy of New 

England, Long Island, and adjacent Georges Bank and Gulf of Maine, in Sibrava, Vladimir, 

12
 
Bowen, D.Q., and Richmond, G.M., eds., Quaternary glaciations in the Northern Hemisphere: 

Quaternary Science Reviews, v. 5, p. 39–52. 

Stone, B.D., 1980, Surficial geologic map of the Worcester North quadrangle and part of the 

Paxton quadrangle, Worcester County, Massachusetts: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1158, scale 1:24,000. 

Stone, B.D., 1978, Preliminary map of surficial deposits of the Gardner quadrangle, Worcester 

County, Massachusetts: U.S. Geological Survey Open-File Report 78–379, 1 sheet, scale 

1:24,000. 

Stone, J.R., London, E.H., and Langer, W.H., 1979, Map showing textures of unconsolidated 

materials, Connecticut Valley urban area, central New England: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–1074–B, 3 sheets, scale 1:125,000. 

Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., 1992, Surficial materials map of 

Connecticut: U.S. Geological Survey Special Map, 2 sheets, scale 1:125,000. 

Stone, J.R., Schafer, J.P., London, E.H., DiGiacomo-Cohen, M.L., Lewis, R.L., and Thompson, 

W.B., 2005, Quaternary geologic map of Connecticut and Long Island Sound basin: U.S. 

Geological Survey Scientific Investigations Map 2784, 2 sheets, scale 1:125,000, and 72-p. 

pamphlet. 

Tucker, R.D., 1977, Bedrock geology of the Barre area, central Massachusetts: University of 

Massachusetts Department of Geosciences, Contribution 30, 132 p. and map, scale 1:24,000. 

Walsh, G.J., 2002, Bedrock geology in the vicinity of the Leicester well site, Paxton, 

Massachusetts: U.S. Geological Survey Open-File Report 2002–433, scale 1:25,000. 

Warren, C.R., and Stone, B.D., 1986, Deglaciation stratigraphy, mode, and timing of the eastern 

flank of the Hudson-Champlain lobe in western Massachusetts, in Cadwell, D.H., ed., The 

Wisconsinan Stage of the First Geological District, eastern New York: New York State Museum 

Bulletin, v. 455, p. 168–192. 

Weddle, T.K., Stone, B.D., Thompson, W.B., Retelle, M.J., Caldwell, D.W., and Clinch, J.M., 

1989, Illinoian and late Wisconsinan tills in eastern New England; a transect from northeastern 

Massachusetts to west-central Maine, Trip A-2 in Berry, A.W., Jr., ed., Guidebook for field trips 

in southern and west-central Maine: New England Intercollegiate Geological Conference, 81st 

Annual Meeting, p. 25–85. 

Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Journal of Geology, 

v. 30, no. 5, p. 377–392. 

13
 
Appendix 

Sources of Data by 7.5-Minute Quadrangle 

Mount Grace Quadrangle 

Map units were reproduced from Hadley (1949). Glacial Stratified Deposits include units Qk and 

Qe of Hadley (1949), which are predominantly coarse-grained glaciofluvial and glaciodeltaic 

sediments graded to small glacial lakes in the valleys of the West Branch Tully River, Mirey 

Brook-Mountain Brook, Darling Brook, and Hodge Brook. Thick-till areas were delineated based 

on topographic analysis. The shallow bedrock unit represents areas of abundant outcrop. Some 

postglacial units were mapped using 2005 orthophoto images. 

Royalston Quadrangle 

Stone, J.R., 1975, unpublished field map; Larsen, F.D., 1980, unpublished field map. Glacial 

Stratified Deposits include predominantly coarse-grained glaciofluvial and glaciodeltaic sediments 

graded to small glacial lakes in the valleys of the East Branch Tully River, Lawrence Brook, 

Beaver Brook, and Millers River. Few bedrock outcrops were mapped in the field in this 

quadrangle; some outcrops in the northwestern part of the map area were mapped from the position 

of structure symbols shown by Springston (1990, pl. 2). Some outcrops were mapped where visible 

on 2005 orthophoto images, and shallow-bedrock areas were delineated using topographic analysis. 

Additional outcrops and shallow-bedrock areas are most likely present, particularly in areas of thin 

till that have steep slopes and (or) irregular topography. Some postglacial units were mapped using 

2005 orthophoto images. 

Winchendon Quadrangle 

Stone, J.R., 1979, unpublished field map. Glacial Stratified Deposits include coarse- and finegrained sediments graded to glacial lakes in the Otter River and Millers River valleys. The shallowbedrock unit represents areas of small scattered bedrock outcrops. Additional bedrock outcrops and 

shallow-bedrock areas are most likely present, particularly in areas of thin till that have steep slopes 

and irregular topography. 

Ashburnham Quadrangle 

Stone, B.D., 1978 unpublished field map. Glacial Stratified Deposits are predominantly coarsegrained glaciofluvial and glaciodeltaic sediments in the Phillips Brook valley and in headwater 

valleys of the Millers River. Bedrock outcrops and shallow-bedrock areas in the eastern part of the 

quadrangle were reproduced from Peterson (1984, pl. 3). Some outcrops were mapped where 

visible on 2005 orthophoto images, and shallow-bedrock areas were delineated using topographic 

analysis. Additional outcrops and shallow-bedrock areas are most likely present, particularly in 

areas of thin till that have steep slopes and (or) irregular topography. Some postglacial units were 

mapped using 2005 orthophoto images. 

14
 
Orange Quadrangle 

Stone, J.R., 1976, unpublished field map; Larsen, F.D., 1980, unpublished field map. Glacial 

Stratified Deposits include predominantly coarse-grained glaciofluvial and glaciodeltaic sediments 

graded to glacial lakes in the valleys of the Millers River and tributaries, Middle Branch Swift 

River, and Whetstone Brook. Distribution of bedrock outcrops and shallow-bedrock areas is from 

Robinson (2008). Some postglacial units were mapped using 2005 orthophoto images. 

Athol Quadrangle 

Map units were modified from Eschman (1966). Glacial Stratified Deposits include predominantly 

coarse-grained glaciofluvial and glaciodeltaic sediments in the Millers River and tributary valleys, 

and in the valleys of the East Branch Swift River, Riceville Brook, and Beaver Brook. The shallowbedrock unit is defined as “areas of numerous small scattered exposures or where bedrock is very 

near the surface and controls the topography” (Eschman, 1966). Thick-till areas were mapped 

based on topographic analysis and on well and test-hole data. Some postglacial units were mapped 

using 2005 orthophoto images. 

Templeton Quadrangle 

Stone, J.R., 1979, unpublished field map. Glacial Stratified Deposits include coarse- and finegrained sediments graded to ice-dammed glacial lakes in the valleys of the Otter River and 

tributaries and sediment-dammed glacial lakes in the Burnshirt River-Trout Brook valley. The 

shallow-bedrock unit represents areas of small scattered bedrock outcrops and where bedrock is 

interpreted to be within 10 ft of land surface. 

Gardner Quadrangle 

Map units were reproduced from Stone (1978). Glacial Stratified Deposits include predominantly 

coarse-grained glaciofluvial and glaciodeltaic sediments graded to small glacial lakes in the valleys 

of the Whitman River and Mahoney Brook and their tributaries. The shallow-bedrock unit is 

defined as “areas where surficial deposits are generally less than 3 meters thick, and may contain 

numerous small bedrock outcrops.” 

Quabbin Reservoir Quadrangle 

Stone, J.R., 1975, unpublished field map. Glacial Stratified Deposits include predominantly coarsegrained sediments graded to a series of glacial lakes in the East, Middle, and West Branch Swift 

River valleys; today these deposits lie mostly underwater beneath Quabbin Reservoir. Bedrock 

outcrops were not mapped in the field. Those shown on the map are visible on 2005 orthophoto 

images. The distribution of shallow-bedrock areas was interpreted by topographic analysis. 

Additional bedrock outcrops and shallow-bedrock areas are present, particularly in areas of thin till 

that have steep slopes and (or) irregular topography. Some postglacial units were mapped using 

2005 orthophoto images. 

15
 
Petersham Quadrangle 

Stone, J.R., 1976, unpublished field map. Glacial Stratified Deposits include predominantly coarsegrained sediments graded to glacial lakes in the East Branch Swift River valley. Bedrock outcrops 

were not mapped in the field. Those shown on the map are visible on 2005 orthophoto images. The 

distribution of shallow-bedrock areas was interpreted by topographic analysis. Additional bedrock 

outcrops and shallow-bedrock areas are present, particularly in areas of thin till that have steep 

slopes and (or) irregular topography. Some postglacial units were mapped using 2005 orthophoto 

images. 

Barre Quadrangle 

Larsen, F.D., 1982, unpublished field map. Glacial Stratified Deposits include predominantly 

coarse-grained sediments graded to glacial lakes in the Ware River valley and its tributary valleys. 

Bedrock outcrop areas are from Tucker (1977). The shallow-bedrock unit represents areas of 

closely spaced outcrops. 

Wachusett Mountain Quadrangle 

Stone, B.D., 1982, unpublished field map. Glacial Stratified Deposits include predominantly 

coarse-grained sediments graded to glacial lakes in the valleys of the East Branch Ware River and 

tributaries, West Branch Ware River, and Wachusett Brook. Bedrock outcrop areas are from 

Tucker (1977). The shallow-bedrock unit represents areas of closely spaced outcrops. 

Winsor Dam Quadrangle 

Stone, J.R., 1976, unpublished field map. Glacial Stratified Deposits include predominantly coarsegrained sediments graded to glacial lakes in the Swift River, Beaver Brook, Flat Brook, and Muddy 

Brook valleys. Bedrock outcrops were not mapped in the field. Those shown on the map are visible 

on 2005 orthophoto images. The distribution of shallow-bedrock areas was interpreted by 

topographic analysis. Additional bedrock outcrops and shallow-bedrock areas are present, 

particularly in areas of thin till that have steep slopes and (or) irregular topography. Some 

postglacial units were mapped using 2005 orthophoto images. 

Ware Quadrangle 

Map units were modified from Mulholland (1975). Glacial Stratified Deposits include 

predominantly coarse-grained glaciofluvial and glaciodeltaic sediments in the valleys of the Ware 

River, Muddy Brook, Mill Brook and tributaries, and Winimusset Brook. Fine-grained deposits 

occur in the subsurface in the Winimusset Brook valley (Stone, B.D., and others, 1992). Some 

bedrock outcrop areas are from Field (1976). The shallow-bedrock unit represents areas of closely 

spaced outcrops. Thick-till areas were mapped based on topographic analysis and on well and testhole data. Some postglacial units were mapped using 2005 orthophoto images. 

16
 
North Brookfield Quadrangle 

Larsen, F.D., 1982, unpublished field map. Glacial Stratified Deposits include predominantly 

coarse-grained deposits graded to sediment-dammed glacial lakes in the Ware River, Sevenmile 

River, and Fivemile River valleys and ice-dammed glacial lakes in the north-draining Bell Brook 

and Burrow Brook valleys. Most bedrock outcrops were not mapped in the field. Those shown on 

the map are visible on 2005 orthophoto images. Additional bedrock outcrops and shallow-bedrock 

areas are present, particularly in areas of thin till that have steep slopes and (or) irregular 

topography. Some postglacial units were mapped using 2005 orthophoto images. 

Paxton Quadrangle 

Stone, B.D., 1982, unpublished field map, western part of quadrangle. Map units in the eastern part 

of the quadrangle were reproduced from Stone (1980). Glacial Stratified Deposits include coarsegrained sediments graded to glacial lakes in the Sevenmile River, Turkey Hill Brook, and 

Asnebumskit Brook valleys. The shallow-bedrock unit in the eastern part of the quadrangle is 

defined as “areas where surficial deposits are generally less than 3 m thick, locally containing 

numerous bedrock outcrops.” Some bedrock outcrops were taken from Walsh (2002). Thick-till 

areas were mapped based on topographic analysis and on the position of drumlin axes shown on the 

map of Stone (1980). Some postglacial units were mapped using 2005 orthophoto images. 

Palmer Quadrangle 

Map units were reproduced from Peper (1978). Glacial Stratified Deposits include coarse-grained, 

glaciofluvial and glaciodeltaic sediments graded to glacial lakes in the valleys of the Swift River, 

Ware River, and Quaboag River and their tributaries. The shallow-bedrock unit is defined as “areas 

of abundant outcrop and thin surficial cover.” Thick-till areas were mapped based on topographic 

analysis and on the position of drumlin axes shown on the map of Peper (1978). 

Warren Quadrangle 

Map units were reproduced from Pomeroy (1977). Glacial Stratified Deposits include coarsegrained glaciofluvial and glaciodeltaic sediments graded to glacial lakes in the Quaboag River 

valley and its tributary valleys. The shallow-bedrock unit is defined as “closely spaced outcrops 

where surficial deposits are thin.” Thick-till areas were mapped based on topographic analysis and 

on the position of drumlin axes shown on the map of Pomeroy (1977). 

East Brookfield Quadrangle 

Map units were reproduced from Pomeroy (1975). Glacial Stratified Deposits include coarsegrained glaciofluvial and glaciodeltaic sediments graded to glacial lakes in the Quaboag River 

valley and its tributary valleys. The shallow-bedrock unit is defined as “closely spaced outcrops 

where surficial deposits are thin.” Thick-till areas were mapped based on topographic analysis and 

on the position of drumlin axes shown on the map of Pomeroy (1975). 

17
 
Leicester Quadrangle 

Stone, B.D., 1982, unpublished field map. Glacial Stratified Deposits include predominantly 

coarse-grained sediments graded to glacial lakes in the French River and Cranberry River valleys. 

Bedrock outcrops were not mapped in the field. Those shown on the map are visible on 2005 

orthophoto images. A few outcrops were located from structure symbols shown on the map of 

Barosh and Johnson (1976). The distribution of shallow-bedrock areas was interpreted by 

topographic analysis. Additional bedrock outcrops and shallow-bedrock areas are present, 

particularly in areas of thin till that have steep slopes and (or) irregular topography. Some 

postglacial units were mapped using 2005 orthophoto images. 

Monson Quadrangle 

Map units were reproduced from Peper (1977). Glacial Stratified Deposits include coarse-grained 

predominantly glaciodeltaic sediments laid down in an ice-dammed glacial lake in the valleys of 

the north-draining Chicopee Brook, Twelvemile Brook, Vinica Brook, Conant Brook, and Foskett 

Mill Stream. The shallow-bedrock unit is defined as “areas of abundant outcrop and thin drift.” 

Thick-till areas were mapped based on topographic analysis and on the position of drumlin axes 

shown on the map of Peper (1977). 

Wales Quadrangle 

Stone, J.R., 1975, unpublished field map. Glacial Stratified Deposits include coarse-grained 

glaciofluvial and glaciodeltaic sediments graded to small glacial lakes in the Quinebaug River 

valley and its tributary valleys. Bedrock outcrops and shallow-bedrock areas were reproduced from 

Seiders (1976), where the shallow-bedrock unit is defined as “areas of thin till and abundant 

outcrop.” Thick-till areas were mapped based on topographic analysis. Some postglacial units were 

mapped using 2005 orthophoto images. 

Southbridge Quadrangle 

Map units were modified from Moore (1978). Glacial Stratified Deposits include coarse-grained 

glaciofluvial and glaciodeltaic sediments graded to small glacial lakes in the Quinebaug River 

valley and its tributary valleys. Bedrock outcrops were reproduced from Moore (1978), and many 

areas of abundant small outcrops were included in the shallow-bedrock unit. Thick-till areas were 

mapped based on topographic analysis and on well and test-hole data. Some postglacial units were 

mapped using 2005 orthophoto images. 

Webster Quadrangle 

Map units were modified from Barosh (1973). Glacial Stratified Deposits include coarse-grained 

glaciofluvial and glaciodeltaic sediments graded to glacial lakes in the Quinebaug and French River 

valleys and their tributary valleys. Bedrock outcrops and areas of shallow bedrock are from Barosh 

(2009) where the shallow-bedrock unit is defined as “areas of abundant outcrops and areas where 

bedrock lies within 3 m of the surface.” Thick-till areas were modified from the Qt3 unit and from 

18
 
the position of drumlin axes, both shown on the map of Barosh (1973). Some postglacial units were 

mapped using 2005 orthophoto images. 

19