Five Ridge Prairie State Preserve

Five Ridge Prairie is a 790-acre preserve at the northern end of the Loess Hills. Located south of Westfield in Plymouth County, it is one of the largest tracts of land in the Iowa State Preserve System. The property was purchased in 1981 by the Plymouth County Conservation Board with assistance from The Nature Conservancy and the Iowa Department of Natural Resources. It was dedicated as a biological and geological state preserve in 1986. 

Directions

1. From the intersection of I-29 and Highway 12 (exit 151) on the west edge of Sioux City, drive 9 miles north on Highway 12 through the town of Riverside and past Stone State Park to the second turnoff for County Road K18. 
2. Turn east (right) onto K18 and go 3.5 miles northeast to 260th Avenue (watch for County Conservation sign). 
3. Turn west (left) and travel 1 mile to the preserve entrance (sign: Five Ridge Prairie State Preserve).

Landscape & Geology

The preserve straddles landscape of dramatic narrow ridges that are separated by deep, wooded valleys, and was named for five major northwest-to-southeast trending ridges that extend through the area. Loess dominates this landscape. The loess originated in the nearby valleys of the Missouri and Big Sioux Rivers. Between 30,000 and 12,000 years ago, these valleys carried large amounts of glacial meltwater and “rock flour” ground from glacial activity to the north. 

Strong winds scoured the silt from broad expanses of exposed floodplain during the drier, low-flow winter seasons and carried the airborne silt eastward out of the valleys. The thickest deposits of loess lie just east of their alluvial sources. The loess is not as thick in this reach of the Loess Hills as it is farther south. Consequently, Cretaceous-age bedrock deposits of marine origin, layers of limestone and shale, can be seen in scattered outcrops throughout the area. These sedimentary rocks are 80 million to 90 million years old. 

Natural Ecosystems

Prairie and woodland are the two dominant natural ecosystems today. The prairies are found on all major ridges, dominating the sunny south and west-facing slopes, and covering approximately 300 acres of the preserve. 

They are dominated by little bluestem and sideoats grama, and contain a blend of plants characteristic of the eastern tallgrass prairie as well as of the Great Plains mixed-grass prairies. Woodland dominated by bur oak cover approximately 370 acres. A dense zone of dogwood and smooth sumac separates the forest from the prairie areas. 

Plants

Approximately 300 plant species are known from the preserve. Twentyfive species are more typically western plants on the eastern edge of their range, such as yucca and cut-leaf iron plant. Starting in late March, pasqueflower blooms on the hillsides. By May and June, the ridges are dotted with blue-eyed grass, hoary puccoon, prairie moonwort, biscuitroot, and Lambert’s crazyweed. The woodlands are also in bloom with spring wildflowers such as bloodroot, bellwort, and Virginia waterleaf. The warm days of summer see a changing display of prairie forbs grasses. 

Wildlife

With both prairie and woodland habitats here, the diversity of birds is great. At least eighty-nine species use the preserve, including grassland birds such as dickcissel and vesper sparrow. In the woodland edges or thickets, western kingbird, blue grosbeak, and northern bobwhite can be found. However, the woodlands have the greatest diversity, with ovenbird, yellow-billed cuckoo, indigo bunting, and scarlet tanager as well as migrating warblers, alder flycatcher, and blue grosbeak. A total of twenty mammals have been noted on the preserve, including:

• Plains pocket mouse
• Northern grasshopper mouse
• White-footed mouse
• Western harvest mouse

The Plains spadefoot toad, Great Plains toad, and the eastern hognose snake can be found here, as well as forty-nine butterflies. 

Hunting is permitted. 

Other natural areas in the vicinity include Broken Kettle Grassland, Sioux City Prairie, Stone State Park, and Mount Talbot State Preserve.