MODERN SEDIMENTS, WATER, AND WETLANDS:  Includes features where recent geologic processes related to erosion and 
transportation of sediment have been occurring.  These map units are Holocene (10,000 years ago until Present) in age and include 
lakes, streams, wetlands, alluvium, and colluvium.
Water:  Open water including lakes and streams.
Wetlands - Organic Sediments:  Partially decomposed plant material, silt, and clay, found in or around shallow lakes, 
marshes, and peatlands.  Wetlands overlie other mapped units.
Alluvial Sediments:  Stratified fine sand, coarse sand, and gravel, with layers of silt, clay, and organics.  The 
sediment is well to very well-sorted.  Alluvium is deposited in streambed and overbank deposits to form features like floodplains,
fans, and terraces.

GLACIAL SEDIMENTS:  Includes all material (clay, silt, sand, gravel, and boulders) that was transported by glaciers and subsequently
deposited directly by the glacier, from the ice as the glacier retreated, or by running water associated with the melting of glacial ice.  
The glacial sediments, which cover the majority of Dodge County, are Pleistocene (2.5 million to 10,000 years ago) in age.
Des Moines Lobe Sediments:  Consists of sediments transported by the Des Moines Lobe glacial ice, meltwater, or wind during 
the Last Glacial Maximum.  This glacial lobe flowed out of Canada through northwestern Minnesota, across southcentral Minnesota, 
and into Iowa.  The easternmost margin of glacial ice deposited sediments along the western edge of Dodge County.  The rock types 
typically associated with Des Moines Lobe sediments include carbonates, granites, and shales.
Loess:  Massive silt, clay, and very fine sand that is greater than 5 feet thick.  The sediment is very well sorted and was 
transported and deposited by wind erosion.  The majority of loess is found in the northeastern corner and east-central 
portion of the county.  Loess also occurs as dunes in the central part of Dodge County.  Loess dunes may contain more 
sand than silt.
Colluvial Sediments:  Poorly sorted clay, silt, and angular fragments of sand, gravel, cobbles, and boulders.  The 
sediment may contain thinly bedded sand lenses and is moderately to poorly sorted.  Colluvium is deposited by slopewash 
or bedrock freeze/thaw processes.  Most of the mapped colluvium is sediment formed by the weathering and mechanical 
breakdown of bedrock due to freeze/thaw processes associated with the last glaciation. Modern colluvium is 
deposited as sediment is washed down slopes and hillsides by alluvial processes and gravity.  
Fluvial Sediments:  Stratified fine and coarse sand, gravel with layers of silt and clay, and pockets of coarse gravel.  The 
sediment is generally moderately sorted to well sorted sand, with gravel scattered throughout.  The sediment was deposited 
from fluvial processes related primarily to meltwater drainages and secondarily to climate fluctuation associated with the 
last glaciation.  Sediment consists of typical rock lithologies associated with the Des Moines Lobe and sediment gradually 
becomes more dominated by local rock lithologies going east. 
Collapsed Outwash Sediments:  Stratified silt, fine sand, coarse sand, and gravel.  The sediment is moderately sorted and 
at one time contained blocks of buried ice.  The surface collapsed when the buried ice blocks melted.  This caused 
depressions and small undulations.  These sediments were deposited as the Des Moines Lobe meltwater flowed south to 
the Cedar River.  This unit is found in the southwestern portion of the county.
Glaciofluvial Fan Sediments:  Silt, fine sand, coarse sand, and some gravel.  The sediment found within most of these 
fans consists of fine sand and silt.  Sediment is moderately to well sorted and is deposited into ponded water on the 
western side of the Des Moines Lobe moraines.  The feature is coarser and thicker on the western portion and becomes 
finer and thinner to the east.
Coalesced Outwash Fan Sediments:  Stratified silt, fine sand, coarse sand, and gravel over till.  The sediment is 
moderately sorted and discontinuous in some places.  The sediment was deposited in pools of water that may have been 
dammed in the south.
Scoured Outwash Channel Sediments:  Stratified silt, fine sand, coarse sand, and some gravel, thinly layered over 
outwash modified till.  Where present, the sediment is moderately to well sorted.  These sediments are remnants of larger, 
surrounding outwash features and/or channels that have been eroded by glacial meltwater.
Glaciolacustrine Sediments:  Silt, clay and fine sand typically deposited in thin layers.  The sediment is moderately well 
to very well sorted.  The interpretation of the sediment is that it is derived from suspended material brought by meltwater 
streams into a basin in western Dodge County.  This deposit of lacustrine sediment thinly covers undifferentiated till. 
Ice Contact Sediments:  Stratified and non-stratified silt, fine sand, coarse sand, and gravel, with layers of clay and 
washed till mixed throughout.  The sediment is found in discontinuous ridges, collapsed lake sediments, and fans.  The 
sediment is poorly to very well sorted.  Landforms are created by water flowing on or in stagnant ice, with the sediments  
deposited as the surrounding ice melts. 
Ice Contact Outwash Channel Sediments:  Stratified and unstratified silt, clay, fine sand, coarse sand, and cobbles over 
Des Moines Lobe till.  The interpretation of the sediment is that a valley carved into, on top of, below, or in between glacial 
ice and formed an outwash channel.  The channel may contain some outwash sediments as well as scoured till.  
Outwash Modified Sediments (Till):  Unsorted clay, silt, sand, gravel, cobbles, and boulders deposited by glacial ice that 
has been scoured and modified by glacial meltwater.  Till is poorly sorted and may be overlain by lenses of moderately to 
well sorted stratified silts, sands and gravel.  Both outwash and till are associated with the Des Moines Lobe.
Supraglacial Sediments (Meltout Till):  Slightly sorted clay, silt, sand, gravel, cobbles, and boulders.  This material was 
deposited from till located on top of and within stagnant glacial ice.  As the ice melted, the till became slightly sorted, 
leaving behind discontinuous patches of sediment.
Stagnant Moraine Sediments (Till):  Unsorted and sorted clay, silt, sand, gravel, cobbles, and boulders deposited as the 
glacier stagnated and melted.  This unit may contain stringers of sorted sand and gravel.  This sediment is associated
with a moraine landform.  Due to incorporation of ice blocks within the sediment during deposition, the resulting landform 
is hilly and undulating.
Ground Moraine Sediments (Till):  Unsorted clay, silt, sand, gravel, cobbles and boulders deposited during the advance 
and retreat of the glacier.  The till is discontinuous and patchy in some places and thinly (<20 feet thick) drapes over 
older, undifferentiated till. There is little relief associated with the deposition of this till.
Moraine Ridge Sediments (Till):  Unsorted clay, silt, sand, gravel, cobbles, and boulders deposited at the margin of a 
glacier.  These ridges are mainly composed of discontinuous till ridges and may contain stringers of sorted silt and sand.  
The ridges represent the easternmost margin of the Des Moines Lobe during the Last Glacial Maximum.

Undifferentiated Glacial Sediments:  Consists of sediments transported by several older glaciers over a long period of time 
(130,000 to 300,000+ years before Present).  Due to the age of these deposits, the landforms have undergone long periods of 
erosion and weathering; therefore there are no constructional features (e.g., moraines, eskers, or kames) associated with these 
glacial tills.  In addition, the surface exposures of a single till, which may have been a continuous layer, is now patchy and 
discontinuous.  Most surface exposures of till units indicate a northwestern source; however there are scattered remnants of  
northeastern-sourced till(s).
Fluvially Modified Undifferentiated Till:  Unsorted clay, silt, sand, gravel, cobbles, and boulders that have been modified 
by fluvial processes.  The till is poorly sorted except for pebble, sand, and silt lags observed on exposed surfaces.  Fluvial 
remnants are discontinuous throughout the unit and contain stratified silts, sands, and gravel.  A majority of these deposits 
are observed where Des Moines Lobe meltwater flowed over older, pre-existing tills.
Quaternary Terrace Sediments:  Stratified fine and coarse sand, gravel with layers of silt and clay, and pockets of coarse 
gravel.  The sediment is generally moderately to well sorted.  These sediments were deposited as meltwater from older, 
northwestern-sourced glaciers utilized pre-existing valleys and deposited sand and gravel.  Due to the age of the deposit, 
the upper 10 feet is very oxidized and has slight to strong cementation.  These sediments are observed 10 to 20 feet 
higher on the sides of existing stream valleys.
Quaternary Outwash Sediments:  Stratified and unstratified fine and coarse sand, gravels with layers of silt and clay, and 
pockets of coarse gravel.  The sediment is generally well sorted, very oxidized in the top 10 feet and can be slightly to 
moderately cemented with calcite or iron oxide.  There are no associated landforms due to a long period of erosion.  In 
addition, some outwash sediment is currently exposed along hill slopes where overlying till sediments are being eroded.  
Indicator pebbles vary between northeastern and northwestern rock types and can be a derivative of both.
Undifferentiated Tills - Upland:  Unsorted clay, silt, sand, gravel, cobbles, and boulders.  Very poorly sorted sediment 
deposited by glacial ice.  Where oxidized, the color is tan to brown, however, the unoxidized tills are mostly dark gray.  
Local lenses of sand and gravel can be observed within and between till units.  Upland till units have been subjected to 
extensive wind erosion, but have not been dissected by stream cutting and therefore are topographically flat. 
Undifferentiated Till - Stream Dissected:  Unsorted clay, silt, sand, gravel, cobbles, and boulders.  Very poorly sorted 
sediment deposited by glacial ice.  There are local lenses of sand and gravel within and between different till units.  Oxidized 
tills are tan to brown in color, while the unoxidized tills are mostly dark gray and occasionally red.  Stream dissected till 
units have been subjected to both wind and extensive stream erosion creating dendritic drainage systems.  Due to 
headward stream erosion, the topography of this mapping unit is undulating (rolling).

BEDROCK UNITS:  Consisting of Ordovician age (458 million to 447 million years ago) exposures of sandstone, shale, and limestone.  
Both younger and older aged rocks are covered by hundreds of feet of glacial sediment.  Rock units exposed in the county include the 
following (from oldest to youngest):  St. Peter Sandstone, Glenwood Shale, Platteville Limestone, Decorah Shale, and the three 
formation members of the Galena Group:  the Cummingsville Limestone, the Prosser Limestone, and the Stewartville Limestone.
Bedrock, Undivided:  Limestone, shale, and sandstone of Ordovician age.  Bedrock was mapped in areas covered by less 
than 10 feet of Quaternary sediment (other than loess).   Bedrock units were observed mostly in and near stream valleys 
in the eastern portion of the county.  Most outcrops of exposed bedrock are limestone from the Galena Group. 
