Illinois Natural History Survey - University of Illinois

ROCK RIVER  

Image of Rock River RRA Castle Rock State park is named for a large outcropping of sandstone along the Rock River. Although this type of sandstone (St. Peter) underlies most of the state, it is exposed at the surface in only a few places. A diversity of natural communities is found here, including ravine, upland and floodplain forest, prairie, stream, and sandstone outcrops. Many plant associations of more northern climates exist in the deep ravines. Relict boreal plants such as native white pine, bunchberry, hairy woodrush, round-leaved shinleaf, and wild sasparilla are found in shaded areas with acidic sandy soil.

 

Map of Site
Land Cover Map of Site

 

ROCK RIVER

Size: 206,215 acres; 322 square miles

Location: North-central Illinois; Boone, Lee, Ogle, and Winnebago counties

The ecological core of this RRA is the Rock River corridor from Rockford to Dixon. Significant features include upland and floodplain forests, seeps, springs, prairies, aquatic systems, cliffs, and bedrock outcroppings. Some of the habitats support relict boreal plants which are more normally found farther north in Wisconsin and Minnesota and in the Appalachian Mountains. Principal landcover in the area is cropland and pasture; forest cover is concentrated along the river. This site is a pilot area for efforts by the Illinois Department of Natural Resources to implement its local partnership program.

LANDCOVER: Cropland is the predominant landcover (47%), followed by grassland (25%) and upland woods (15%). This RRA ranks 15th in percentage of upland woods. The percentages of nonforested wetland and bottomland forest are low compared to the other RRAs (24th and 28th, respectively).

NATURAL AREAS: The 20 Natural Areas range from less than an acre (Stronghold Hill Prairie) to 2,311 acres (Lowden-Miller Forest). Nachusa Grasslands is the second largest Natural Area with 1,583 acres.

BIOLOGICALLY SIGNIFICANT STREAMS : BSS designated streams are a nearly seven mile stretch of the Rock River and the entire length of the Kishwaukee River in this RRA.

HERITAGE SITES : There are 101 Heritage occurrences consisting of seven significant community types, 32 plants species, eight animal species, and a rookery.

STATE AND FEDERAL LAND: There are three state parks within the site and one state forest.

NATURE PRESERVES : Four Nature Preserves are present and contain such significant features as upland forest, sandstone cliffs, gorges, and prairie.

NATURAL DIVISIONS :This RRA is within the Rock River Hill County (84%), Northeastern Morainal (11%), and Grand Prairie (5%) Natural Divisions. This site has the largest acreage of the Rock River Hill Country division among the RRAs.


 

SUMMARY OF SITE CHARACTERISTICS: SIZE, BIOLOGIC RESOURCES, AND PUBLIC LANDS

Total Acreage

    206,215

Natural Areas

    Acreage

5,416

    Number

20
Biologically Significant Stream Mileage 17.5
Natural Heritage Sites 101
State Land

    State Parks

3

    State Conservation Areas

0

    State Forests

1

    State Fish & Wildlife Areas

0

    Acreage

4,706

    Percentage of RRA

2.3
Federal Land

    Acreage

0

    Percentage of RRA

0.0

 


 

LANDCOVER

    Acres

    % of RRA

Upland forest 30,458.06 14.77
Bottomland forest 2,552.41 1.24
Wetland-nonforested 608.75 0.30
Grassland 50,586.08 24.53
Cropland 96,519.14 46.81
Urban/Built-up 21,146.41 10.25
Water 4,340.92 2.11
Total 206,211.77 100.01

 


 

ILLINOIS NATURAL AREAS INVENTORY SITES

    Acres

Babson Hollow 4
Bell Bowl Prairie 21
Byron Dragway Prairie 16
Castle Rock 644
Commonwealth Edison Prairie 147
Fearer Tract At Castle Rock 145
Franklin Creek 148
Grand Detour Yellow Birch Site 11
Jarrett Prairie 140
Kishwaukee River 129
Lowden Memorial State Park 22
Lowden-Miller Forest 2,311
Mount Morris East Geological Area 10
Nachusa Grasslands 1,583
Oregon Geological Area 7
Rock River Yellow Birch Stand 7
Silver Creek Prairie 4
Sinnissippi Cornus Canadensis Site 2
Stronghold Hill Prairie < 1
White Pines Forest State Park 64

 


 

BIOLOGICALLY SIGNIFICANT STREAMS

    Miles

Kishwaukee River 10.7
Rock River, Honey Creek to Clear Creek 6.8

 


 

NATURAL HERITAGE CATEGORIES
Communities Occurrences

    Types/Species

    Wetland

3 2
Communities

    Forest

4 2

    Prairie

3 3
Threatened and Endangered Animals

    Bird

9 6

    Mammal

1 1

    Reptile

2 1
Threatened and Endangered Plants

    Plant-Dicot

47 17

    Plant-Monocot

11 7

    Plant-Fern/Fern Ally

15 8
Geological Feature 5 1
Other

    Rookery

1 1

 


 

STATE AND FEDERAL LAND
State Parks

    Acres

    Castle Rock

1,793

    Lowden

205

    White Pine Forest

397
State Conservation Areas 0
State Forests

    Lowden-Miller

2,311
State Fish and Wildlife Areas 0
Federal Land 0

 


 

ILLINOIS NATURE PRESERVES

    Acres

Franklin Creek 100
George B. Fell 670
Jarret Prairie 102
Severson Dells 21

 


 

NATURAL DIVISIONS

    Acres in RRA

    % of RRA

    % of Division

Rock River Hill Country 173,663 84.2 11.5
Northeastern Morainal 22,274 10.8 0.9
Grand Prairie 10,279 5.0 0.0

 




Illinois Natural History Survey

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