Hole in the Mountain Prairie

Things to Look For

The Hole-in-the-Mountain Prairie is an 1,157-acre prairie and oak savanna wildlife preserve located south of Lake Benton along Highway 75.  The preserve is owned and managed by The Nature Conservancy. The best time of year to visit is Spring through Fall, during the wildflower blooming season.

The preserve is good habitat for rare prairie-dependent insects including 25 species of butterflies, including:

Dakota skipper (Hesperia dacotae)
Ottoe skipper (Hesperia ottoe)
Uncas skipper (Hesperia uncas)
Pawnee skipper (Hesperia leonardus pawnee)

The inconspicuous Dakota skipper has a wingspan of 1 to 1 1/2 inches, is yellow or straw colored, and has an erratic darting flight. It was first discovered near Volga, South Dakota, and survives on only a few scattered virgin prairie habitats in the Dakotas, Iowa, and Minnesota.

There are over 60 species of grasses, sedges, and rushes, 10 species of trees and shrubs, and 200 species of wildflowers found here. Native plants include:

Lotus milk-vetch (Astragalus lotiflorus)
Small-leaved pussytoes (Antennaria parvifolia)
Small white lady’s slipper (Cypripedium candidum)
Red threeawn (Aristida longiseta)
Soft goldenrod (Solidago mollis)
Slender milk-vetch (Astragalus flexuosus)

Ecological Description
Hole-in-the-Mountain Prairie is a large prairie remnant situated on a steep valley along the outer edge of the glacial escarpment (cliff) known as the Prairie Coteau. This is a highly dissected landscape characterized by a topographic variation of more than 100 feet, situated immediately south of the Bemis Moraine.

The underlying parent material is a deep, stony, calcareous till dating back to the Wisconsin glaciation 18,000 to 12,000 years ago. The till is exposed on steep, eroded side slopes, while the flat ridge tops are covered by a veneer or loess (wind-deposited loam). On the concave foot slopes and drainage ways, the till is buried beneath a dark layer of rich soil washed out of the higher ground. Wet prairies and cattail/bulrush marshes occupy the level valley bottom.

The preserved is managed by prescribed burning and the native prairie vegetation on the steeper slopes has recovered well in recent years. Areas of old fields are being replanted to native species.

History & Use
Hole-in-the-Mountain Prairie is a part of a 4,300 acre prairie area that begins at the south end of the City of Lake Benton and runs south toward the Altona State Wildlife Management Area. The prairie valley is the headwaters of Flandreau Creek, which runs toward the Big Sioux River. Native Americans called the half-mile-wide valley "Mountain Pass" or "Hole-in-the-Mountain".

The first tract of the preserve was acquired in 1978. Several tracts adjacent to the preserve were purchased by The Nature Conservancy and transferred to the Minnesota Department of Natural Resources (DNR) as Wildlife Management Areas. In addition, 3,400 acres of this prairie area ecosystem are privately owned and managed.

Historically, most of this land had been used to pasture sheep and cattle on the steep slopes and parts of the floodplain. The upland flats were cultivated. When acquired by The Nature Conservancy, most areas had been altered to some extent from their pre-settlement condition — the vegetation had shifted from taller prairie grasses such as big and little bluestem and Indian grass to drier species characteristic of prairies farther west such as needlegrasses, wheatgrasses, and grama grasses.

More Information?
If you want to know more about this area, or about the work of The Nature Conservancy, contact:
The Nature Conservancy,
Minnesota Chapter, 1313 5th Street SE, Minneapolis, MN 55414

VISITING THE PRESERVE
From the City of Lake Benton, go south on U.S. Highway 75 for 1.5 miles and park at the turn-out along the west side of the highway. The best time to visit is spring and fall, during the wildflower season.