the park. The Pothole Trail, also 

 on the Wisconsin side, shows oft 

 several glacial potholes, including 

 the "perfect" one, as well as spec- 

 tacular views of the St. Croix 

 River gorge and a cliff formation 

 known as the Old Man o' the 

 Dalles (dalles — the word rhymes 

 with "pals" — are rapids in a river 

 confined between steep canyon 

 walls) . 



Another Pothole Trail, on the 

 Minnesota side of the river, gives 

 visitors a tour of some large 

 glacial potholes. One of them is 

 twelve feet across the top and 

 sixty-seven feet deep; another is 

 nearly forty feet across and about 

 forty feet deep. A small flower- 

 ing plant known as waterwort 

 grows in several of the potholes 

 that contain standing water. 



Robert H. Mohlenbrock is a 

 distinguished professor emeritus of plant 

 biology at Southern Illinois University 

 Carboudale. 



Rock climber tackles a pothole wall. 



VISITOR INFORMATION 



Interstate State Park 



P.O. Box 703 



St. Croix Falls, Wl 54024 



715-483-3747 



dnr.wi.gov/org/land/parks/specific/interstate 



Interstate State Park 

 P.O. Box 254 

 Taylor Falls, MN 55084 

 651-465-5711 



www.dnr.state.mn.us/state_parks/interstate 



channels, the potholes were left ex- 

 posed at their margins. 



Although the potholes were shaped 

 mostly by sand and gravel, boulders, 

 too, were whirled around inside the 

 potholes, and the boulders' edges were 

 gradually rounded off. Today those 

 boulders are shaped like cannonballs, 

 some as large as four feet in diameter. 

 Visitors to the Ice Age Interpretive 

 Center can stand in awe of several of 

 them, stationed outside the front doors 

 of the center, on the Wisconsin side of 



Sulphur fungus (Polyporus sulphureus) 



Habitats 



Bluff top The dry bluff tops are home 

 to plants and short trees that can sur- 

 vive on limited moisture. The most 

 common tree is bur oak; others in- 

 clude eastern red cedar, hop horn- 

 beam, jack pine, white ash, and white 

 oak. Creeping juniper, a sprawling 

 shrub, is nestled among large boul- 

 ders; eastern prickly pear grows in the 

 open among the rocks. Poverty oat 

 grass, with curly leaves at the base 

 and slender flowering spikes, thrives 

 in the dry, rocky soil. Common poly- 

 pody and rusty cliff fern, two low- 

 growing ferns, live in rock crevices. 



Wildflowers include Canada 

 columbine, common yarrow, divari- 

 cate sunflower, golden corydalis, 

 harebell, Pennsylvania sedge, penny- 

 royal, prairie alumroot, shining bed- 

 straw, spreading dogbane, starry 

 false Solomon's seal, and tall cory- 

 dalis. Sand fameflower, a summer- 



blooming succulent, opens its blos- 

 soms each day for only an hour, at 

 about two o'clock in the afternoon. 



Moist woods The ravines harbor moist 

 woods dominated by basswood, bit- 

 ternut hickory, hop hornbeam, paper 

 birch, sugar maple, white ash, and 

 white oak. The shrub layer is sparse, 

 though snowberry is fairly common. 

 Most of the wildflowers in the under- 

 story are spring bloomers; they in- 

 clude bland sweet cicely, Canada 

 anemone, common blue violet, com- 

 mon enchanter's nightshade, eastern 

 waterleaf, false Solomon's seal, red 

 baneberry, Solomon's seal, white 

 avens, wild geranium, and wild ginger. 



Upland woods On the upper slopes 

 of the ravines are relatively dry wood- 

 lands dominated by northern red oak, 

 slippery elm, white ash, and wild 



black cherry. The wildflowers of this 

 habitat bloom mostly in summer and 

 fall; they include American figwort, 

 forest lousewort, lopseed, old-field 

 five-fingers, tall white beardtongue, 

 wild bergamot, and zigzag golden- 

 rod. Crested wood fern, rattlesnake 

 fern, and toothed wood fern are scat- 

 tered throughout the woods. 



Seeps Water seeps from fissures in 

 many of the cliffs, often draining into 

 depressions where boglike conditions 

 prevail. These low areas are often 

 covered by masses of mosses, includ- 

 ing sphagnum. Numerous species of 

 sedge also grow here, some forming 

 mounds. Among the other plants are 

 boneset, jewelweed, marsh fern, 

 marsh marigold, northern blue flag, 

 sensitive fern, skunk cabbage, swamp 

 saxifrage, water scorpion grass, and 

 white turtlehead. 



June 2006 natural HISTORY 



55 



