Castle Rock State Park is located along the west bank of the Rock River three miles south of Oregon, Illinois in Ogle County. The Rock River drains the rolling topography of the park, which contains sandstone bluffs, rock formations, ravines and unique northern plants characteristic of this region. Castle Rock consists of approximately 2,000 acres, 710 of which are in the George B. Fell Nature Preserve, designated as an Illinois Nature Preserve. The site was dedicated as a state park in 1978.
Native Americans inhabited the Castle Rock State Park region until 1730 when the Sauk and the Fox tribes, who were being forced westward by the colonists, invaded and took over.
New Englanders settled what is now the Castle Rock region in the early 19th century. A group called Friends of our Native Landscape proposed creating a state park in the area ? they acquired some land that they described as "a unique wilderness remnant of great natural beauty and scientific interest."
In 1964, the Natural Lands Institute, a non-profit natural lands preservation group, conducted a public fundraising campaign to preserve part of the Castle Rock area. Castle Rock was recognized in the state of Illinois as an outstanding area of major scientific importance in 1965.
Land acquisition by Illinois began in 1970.
Castle Rock State Park consists of dry mesic forest, upland ridges, mesic ravines, a small fen, scattered forest edges and a floodplain forest.
The adjacent Lowden-Miller State Forest, immediately across the Rock River, consists of 2,225 acres of deciduous and coniferous forest at various stages, including former clearcuts and an evergreen nursery. It holds habitat for many rare breeding songbirds in the state.
The Lowden-Miller State Forest and Castle Rock State Park combine to host an impressive variety of rare breeding warblers and other songbirds. State biologists did intensive bird research here in 1993 and 1994 and found small nesting populations of several bird species either rare or absent from much of the state, including Black-throated Green Warbler, Cerulean Warbler, Canada Warbler, Hooded Warbler, Worm-eating Warbler, Chestnut-sided Warbler and Golden-winged Warbler. Other breeding songbirds include Wood Thrush, Yellow-throated Vireo, Acadian Flycatcher, Rose-breasted Grosbeak, Yellow-billed Cuckoo and Black-billed Cuckoo.
Hawks that breed in the park or state forest include Broad-winged and Cooper's. Barred Owls, Red-headed Woodpeckers, Whip-poor-wills and Wild Turkeys also use the region for breeding.
This site was chosen as an IBA because it met the criteria for Cerulean Warbler and Blue-winged Warbler
This particular area is on the Sandwich fault zone characterized by deep ravines and sandstone outcroppings. The climate at the site is continential. Plants are representative of dry-mesic upland forest, mesic upland forest, wet-mesic floodplain forest and seep communities.