York Prairie features remnants of tallgrass prairie within an agricultural landscape and includes high quality patches of dry-mesic prairie with over 100 species of native prairie plants, cliffs, and springs. Eight rare plants are found here including the federally threatened prairie bush-clover (Lespedeza leptostachya). Today, only 19 populations of the rare prairie bush clover exist in Wisconsin and with restoration, York Prairie has the potential to provide the largest acreage of prairie bush clover in the state. Numerous other rare plants are found here including prairie thistle (Cirsium hillii), prairie Indian plantain (Arnoglossum plantigineum), cream gentian (Gentiana alba), wild quinine (Parthenium integrifolium), pomme-de-prairie (Psoralea esculenta), Richardson's sedge (Carex richardsonii), and marble-seed (Onosmodium molle). Ten prairie-restricted insects have been found here and the state-endangered regal fritillary butterfly is also found in the area. Additionally, York Prairie provides critical habitat for four declining grassland birds which breed here including the state-threatened Henslow's sparrow (Ammodramus henslowii), grasshopper sparrow (Ammodramus savannarum), upland sandpiper (Bartramia longicauda), and western meadowlark (Sturnella neglecta). Four of John Curtis' Vegetation of Wisconsin (1959) study sites were located within this area. York Prairie is owned by the DNR and was designated a State Natural Area in 2002.