Return to Home Page
Watershed Description
General Description Geology Soils & Historic Vegetation Unique Features Wetlands Natural Areas DemographicsThe Yellow River watershed encompasses approximately 154,500 acres in Allamakee, Clayton and 
Winneshiek Counties in northeast Iowa. The river and its tributaries are 360 miles in length.
The elevation of the Yellow River Basin ranges from 655 feet at the mouth to 1250 feet along the uppermost boundary of the watershed.
According to A. N. Strahler (1952) Dynamic basis of geomorphology, Geological Society of America Bulletin 63:923-938, the Yellow River ranges from stream order 1 in the upper watershed and tributaries to stream order 4 at the mouth (confluence with the Mississippi River). The most complex river systems reach an order of 7.
All of the bedrock in this area of Iowa dates to the Ordovician Period (490 - 443 million years ago), the second period of the Paleozoic Era (543 - 248 million years ago), which 
was characterized by the appearance of primitive fishes.
Bedrock (youngest to oldest rock formations)
Maquoketa Formation; Neda, Brainard, Fort Atkinson, Clermont, Elgin members, Upper Ordovician (Richmondian) is found along the southern one-third of the watershed. The maximum thickness is 275 feet (85 m).
Primary lithologies include shale, green-gray, dolomitic, dolomite and limestone, variably argillaceous to cherty; limestone fossiliferous, part cherty.
Secondary lithologies: shale, brown, graphtolitic (lower part).
Minor: phosphorite and phosphatic dolomite (basal part); oolitic ironstone and red mudstone (locally at the top).
Galena Group and Platteville Formation are found in the remainder of the upper watershed and the southern area of the lower watershed. This includes thin interval of Glenwood Shale at base; Middle and Upper Ordovician (Blackriveran, Chatfieldian, Edenian, Maysvillian, basal Richmondian).
Maximum thickness total interval: 320 ft (98 m); max. Galena Group (Dubuque, Wise Lake, Dunleith, Decorah formations) 275 ft (85 m); maximum Platteville (McGregor, Pecatonica members) 55 ft (17 m); maximum Glenwood 10 ft (3 m).
Primary lithologies: limestone, fossiliferous, variably dolomitic, part cherty; dolomite, fossil-moldic to vuggy.
Secondary lithologies: shale, green-gray, calcareous (Decorah); shale, green-gray, non-calcareous, part sandy (Glenwood); limestone, argillaceous; nodular chert.
Minor: dolomite, part sandy (Pecatonica); shale, dark brown, organic (Decorah); sandstone, vf-m (Glenwood).
Prairie due Chien Group and St. Peter Sandstone is found in the lower channels of the Yellow River. This includes the upper Jordan Formation (Coon Valley member). Lower Ordovician (Ibexian, Canadian) and Middle Ordovician (Chazyan-lower Blackriveran).
Maximum thickness total interval: 400 feet (122 m); maximum Prairie du Chien Group (Shakopee, Oneota formation) 290 feet (88 m); maximum St. Peterson 220 feet (67 m); maximum upper Jordan 50 ft (15 m).
Primary lithologies: dolomite, part vuggy, part cherty (Oneota); dolomite, variably sandy, cherty, oolitic, interclastic, and stromatolitic (Shakopee, Coon Valley); sandstone, vf-m (St. Peter).
Secondary lithologies: sandstone, vf-m (Shakopee); chert, nodular, part oolitic.
Minor: shale, green-gray; chert conglomerate.
The Cambrian, Jordan Sandstone, St. Lawrence Formation and Lone Rock Formation are found at the mouth of the Yellow River. Upper Cambrian (Trempealeauan-Franconian; 
Sunwaptan-Steptoean).
Maximum thickness total interval: 360 ft (110 m); maximum Jordan (Waukon, Van Oser, Norwalk, Waukon members) 125 ft (38 m); maximum St. Lawrence (Lodi, Black Earth members) 120 ft (37 m); maximum Lone Rock 140 ft (43 m).
Primary lithologies: sandstone, vf-m (Jordan); siltstone, dolomitic, and silty to sandy dolomite (St. Lawrence); sandstone, vf-f, silty to argillaceous, glaucontitic greensand (Lone Rock).
Secondary lithologies: sandstone, f-c (Van Oser member); shale, gray to green, part glauconitic (Lone Rock).
To date, in the Yellow River watershed, 2918 sinkholes have been identified primarily in the Galena-Decorah-Platteville Groups although a few of these are also present in the St. Peter Sandstone Formation and the Prairie du Chien Group.
Data has been collected on 247 geologic sampling sites within the watershed. Of these, 245 are well logs and 2 are outcrop samples. The two outcrop samples were taken at Effigy Mounds National Monument in 1990.
In 2000, there were eighteen quarries operating in the Yellow River Watershed Basin for a total of 1,044 acres. These were distributed throughout the watershed primarily in the Galena-Decorah-Platteville Formations.
Surficial deposits made during the Quaternary period, (Glacial Age) (1.5 million years ago to present) average 25 feet in depth throughout most of the watershed. Surficial 
deposits along the edge of the watershed in isolated areas average 75 feet in depth while in the lower reach and at the mouth of the Yellow River they average 150 feet in depth.
The Yellow River Watershed Basin is comprised of 12,661 acres of alluvial deposits, which comprise approximately 8% of the basin. These are found within the main channel of the Yellow River. Alluvial deposits are those sediments which are deposited by flowing water within a stream floodplain.
The major soil series found within the Yellow River watershed are Fayette (52,600 acres - 34%), Downs (38,000 acres - 24.5%), Nordness (13,000 acres - 8.4%), and Dubuque (11,000 acres - 7.1%). Seventy-six other soil series make up the remaining 26.4% of the area. The four major soils are all alfisols, soils which developed under forest covers in humid midlatitudes. Fayette, Downs and Dubuque soils were formed in loess, a buff to gray, fine grained calcareous silt or clay, thought to be a deposit of wind-blown dust.
The Fayette series consists of very deep, well drained, fine silty alfisol formed in loess. These convex crests, interfluves (gully boundary lines) and side slopes on uplands and on treads and risers on high stream terraces. Slopes range from 0 to 60 percent. Mean annual air temperature is about 49 degrees F. Mean annual precipitation is about 33 inches. These are well drained soils. Saturation does not occur within a depth of 6 feet during the wettest periods of the normal year. Surface runoff potential is negligible to high. The native vegetation is deciduous trees, mainly oak and hickory. These soils occur throughout the steeper portion of the Yellow River drainage basin along the Yellow River itself.
The Downs series consists of very deep, well drained, fine silty alfisol formed in loess. These soils are on interfluves and side slopes on uplands and on treads and risers of stream terraces. Slopes range from 0 to 25 percent. Mean annual air temperature is about 47 degrees F. Mean annual precipitation is about 34 inches. These are well drained soils. Saturation does not occur within a depth of 6 feet during the wettest periods of normal years. Surface runoff potential is negligible to high. The native vegetation is big bluestem, little bluestem, switchgrass, other grasses of tall grass prairie and widely spaced oak and hickory. These soils occur in the uplands of the tributaries and the upper reaches of the watershed.
The Nordness series consists of shallow, well drained, loamy alfisol formed in loamy or silty material and a paleosol over limestone rock. These soils are on high structural benches, crests, and convex sides slopes on uplands. Slopes range from 2 to 40 percent. Mean annual air temperature is about 47 degrees F. Mean annual precipitation is about 33 inches. These are well drained soils. Saturation does not occur within a depth of 6 feet during the wettest period of most years. Surface runoff potential is low to high. The native vegetation is deciduous trees, dominantly hickory and oak. These soils are found in the tributary valleys.
The Dubuque series consists of moderately deep, well drained, fine silty alfisol formed in 18 to 36 inches of loess and a thin layer of residuum from limestone bedrock or reddish paleosol high in clay overlying limestone bedrock. These soils are on ridges of narrow interfluves and side slopes on uplands and high structural benches. Slopes range from 2 to 60 percent. Mean annual air temperature is about 47 degrees F. Mean annual precipitation is about 33 inches. These are well drained soils. Saturation does not occur within a depth of 6 feet during the wettest period of most years. Surface runoff potential is low to high. The native vegetation is deciduous trees. These soils are found along the steep edges of the lower watershed valleys and the upper watershed valleys.
|
Algific Talus Slopes 
|
These ecosystems, which are rare and almost unknown, are found in the Driftless Area of Iowa, Wisconsin, Minnesota, and Illinois. The unusual geology of these north to northeast facing slopes keep them cool in summer and warm in winter. Small ice caves are found behind steep slopes of limestone which are scattered with loose rock (talus) at the base. In the summer, warm air is drawn down through sinkholes into these ice caves, cooled, and then escapes through vents in the slopes. In winter, the air in the caves is warmer than the outside air, which then reverses the air flow. As the warm air rises and exits the sinkholes, cold air is drawn in through the talus vents, freezing the ground water.
These cold microhabitats allow northern species and periglacial relicts (species of from glacial times) to persist. Of primary importance are the Iowa Pleistocene snail, and northern monkshood (a plant with blue hood-shaped flowers). The woody overstory is often sparse, with scattered black ash (Fraxinus nigra) and paper birch (Betula papyrifera). Mountain maple (Acer spicatum), a northern shrub, may be frequent. Extensive beds of bulblet fern (Cystopteris bulbifera) and mosses are characteristic. The endangered Iowa Pleistocene snail (Discus macclintocki) is known from fossil records to have existed 400,000 years ago. It found its current home about 10,000 years ago as ice age conditions moderated. This snail occurs nowhere else in the world but on the algific talus slopes in the Driftless Area. It shares its habitat with a host of rare and disjunct (separated from their normal range) plants and animals associated with cool habitats. Balsam fir (Abies balsamea), Canada yew (Taxus canadensis) and yellow birch (Betula alleghaniensis) are common to algific talus slopes. The threatened Northern monkshood plant (Aconitum noveboracense) also grows on these sites. Northern monkshood can also be found on cool sandstone cliffs. This plant is found in Iowa, Wisconsin, Ohio and New York. The invasion of garlic mustard (Alliaria petiolata) onto algific talus slopes has become a threat in recent years. |
||
|
Oak Savanna 
|
Oak savanna is a community of scattered oak trees, usually bur oak (Quercus macrocarpa) although white oak and some red oak may be present. The trees tower above a layer of prairie grasses and forbs (flowering plants). The trees have spreading limbs and the grasses and forbs are exposed to sunlight. Oak savanna is a transitional community between prairies and woodland environments, historically influenced by a recurring natural fire regime. Oak savannas may also be found on warmer and drier sites. Oak trees found in a savanna setting usually have large lower branches, which indicate that they developed without competition from nearby trees. The oaks are fire resistant while other species such as walnut, elm, maple and ash are not. Fire in an oak savanna is confined to the ground (leaf and grass litter). Oak savannas may also be called oak openings or oak barrens. Today, these ecosystems are few in numbers. They have either converted to forest land because of lack of natural disturbances or have been cleared for pastures and crop lands. |
||
|
Pine relicts 
|
These isolated stands of white pine (Pinus strobus) which occur on sandstone and limestone outcrops or in thin soils over sandstone or limestone in the Driftless Area of northeast Iowa, are known as pine relicts. Eastern white pine is found from Newfoundland west to extreme southeastern Manitoba and south to the Great Lake States. It is also found along the Atlantic coast from Maine to New Jersey, in the Appalachian Mountains to northern Georgia. It also occurs in Iowa, western Kentucky, western Tennessee, and Delaware. White pine was extensively logged in the late 1800s in the north central states and is not as common as it once was. In mixed hardwood forests, it often occurs as a super dominant tree towering above the surrounding hardwoods or as isolated communities. |
The Yellow River watershed contains wetlands totaling 1,775 acres. Of this area
- 3.7% are seasonally flooded flats or basins;
- 2.8% are wet meadows;
- 8.4% are shallow marshes;
- 1.8% are deep marshes
- 25.0% are shallow open water;
- 2.9% are shrub swamps;
- 33.6% are wooded swamps;
- 2.1% are municipal and industrial ponds;
- and 19.6% are associated with the Yellow River and Mississippi River systems.
Most of the wetlands not associated with the river systems are small in size, usually less than 1 acre.
The Iowa Department of Natural Resources land 
lying within the Yellow River Watershed includes the Yellow River Unit (1051 acres) and the Lost 40 Unit (161 acres) of the Yellow River State Park. The Yellow River Unit is located on the Yellow River 2.5 miles upstream from the mouth with the Mississippi River. The Lost 40 Unit is 3.5 miles upstream of the mouth of the Yellow River.
The Heritage Unit, the North Unit and the west half of the South Unit (2,122 acres) of Effigy Mounds National Monument lie within the Yellow River Watershed.
There are no municipalities lying totally within the watershed but the following are found along the periphery. Populations are shown in 20 year increments.
| 1880 | 1900 | 1920 | 1940 | 1960 | 1980 | 2000 | Change | |
| Ossian | 444 | 670 | 858 | 822 | 827 | 829 | 853 | +192% |
| Castalia | 272 | 239 | 216 | 188 | 175 | -36% | ||
| Postville | 732 | 984 | 1039 | 1194 | 1554 | 1475 | 2273 | +311% |
| Luana | 181 | 204 | 276 | 246 | 249 | +138% | ||
| Monona | 420 | 674 | 1049 | 1191 | 1346 | 1530 | 1550 | +369% |
| Waukon | 1350 | 2153 | 2359 | 2972 | 3639 | 3983 | 4131 | +306% |
Average farm size (acres) for each county is as follows:
| 1890 | 1910 | 1930 | 1950 | 1969 | 1987 | 1997 | Change | |
| Allamakee | 150 | 167 | 176 | 188 | 249 | 302 | 309 | +206% |
| Clayton | 135 | 151 | 155 | 165 | 215 | 264 | 276 | +204% |
| Winneshiek | 144 | 148 | 148 | 157 | 198 | 231 | 249 | +173% |
County population for each county is as follows:
| 1850 | 1860 | 1880 | 1900 | 1920 | 1940 | 1960 | 1980 | 2000 | |
| Allamakee | 777 | 12237 | 19791 | 18711 | 17285 | 17184 | 15968 | 15108 | 14675 |
| Clayton | 3873 | 20728 | 28829 | 27750 | 25032 | 24334 | 21962 | 21098 | 18678 |
| Winneshiek | 546 | 13942 | 23938 | 23731 | 22091 | 22263 | 21651 | 21876 | 21310 |
County populations saw a dramatic increase during settlement from 1850 to 1860. Populations of all three counties reached their peak in 1880. Today, Allamakee County has 74.1% of the population it had in 1880, Clayton County has 64.8%, and Winneshiek County has 89.0%. This data was available at the county level only, and not by watershed.