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.

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