Cayler Prairie State Preserve is a 160-acre remnant of tallgrass prairie in northwestern Iowa near Spirit Lake, protected as one of the state's last surviving old-growth prairies and recognized as a National Natural Landmark. Dominated by big bluestem and a succession of seasonal wildflowers, it also adjoins managed wetlands within a larger 1,204-acre land complex long associated with wildfowl hunting. Its preservation began when botanist Ada Hayden recognized the site's importance in 1944 after finding prairie plants in a hayfield. The Cayler family sold the land to the Iowa Conservation Commission in 1958, and the prairie later received landmark, preserve, and bufferland protections.