Extraordinary Potholes on the St. Croix River
Total Page：16
File Type：pdf, Size：1020Kb
The Kathy M carries tourists on a sightseeing excursion on the St. Croix River. Interstate State Park is at right. Extraordinary Potholes on the St. Croix River Workers at Interstate State Park recently re-excavated two of the park's more than 200 potholes—cylindrical holes bored into some of the hardest bedrock in the world. These remarkable natural holes range from coffee-cup size to the world's deepest "Bottomless Pit" Dave Crawford AY "pothole" and most people Interstate's potholes are different Spicture the suspension-wrecking from most Minnesota potholes. They craters that pepper Minnesota's roads date from a big "spring thaw" about after each spring thaw. So when peo- 10,000 years ago. Melting glacial ice ple learn that the Department of Nat- carved out enormous river valleys. ural Resources is restoring potholes Today, the St. Croix River occupies at Interstate State Park near Taylors one of these valleys. Falls, Minn., they may wonder why. At Interstate State Park, the roar- JULY-AUGUST 1988 27 St. Croix Potholes ing river of meltwater encountered an outcrop of basalt rock—some of the world s hardest bedrock—and formed a giant rapids. Aided by sand and silt suspended in the fast-moving water, swirls and back-eddies in the rapids ground away the basalt. The tremen- dous power of the swirling water cre- ifeJ ated the world's deepest glacial potholes. Top, left: The "Bottomless Pit." Top, right: In 1850, Swedish author and trav- Looking up 60 feet from deepest pothole. eler Frederika Bremer visited the Above: Spiral form of potholes. potholes. She later wrote that the gorge of the St. Croix was "one of hidden by soil. Some had trees grow- God's beauteous spots on earth.'' ing in them, while rainwater filled Other world travelers over the years others nearly to the brim. remarked on the spectacular beauty and incomparable features of this spot. Rock Wells. Records of these early By 1895, support for the preserva- excavations are scarce, but some hints tion of these features resulted in the can be found in newspaper and mag- creation of Interstate State Park by azine articles from the late 1890s. In cooperative legislation in Minnesota 1897, an article in Northwest Maga- and Wisconsin. zine said: One of the park's first projects was "The rock wells, or pot holes,' were to clean the potholes to make them few in number and partially or wholly more visible to tourists. Most pot- filled with debris.... Many of these holes were partially or completely wells have been cleaned, and so many new ones have been discovered that Dave Crawford is a park naturalist at the Minnesota side is literally honey- Interstate State Park, Taylors Falls. combed with these curious remind- 28 THE MINNESOTA VOLUNTEER Left: Opening entrance to the "Bake Oven" pothole. Construction workers used jack- hammers to break rocks. Right: Worker rappels into "Bottomless Pit" to begin arduous task of removing tons of rock and mud from five-story-deep pothole. ers of titanic forces which formed tempting targets for visitors who cavities in the rock from a few inches dropped rocks into them to try to in width and depth to ten or twelve guess their depth. Many small pot- feet in diameter—and to unknown holes had vanished completely under depth." the onslaught of rocks, pine needles, In f899, well-known geologist and pennies, and pop cans. historian Warren Upham said Inter- Efforts were made to clean up lit- state had 75 potholes. A year later he ter and keep major potholes pumped revised the number to more than 80. out for visitors to see, but only a major By 1905, the count exceeded 100. But, project could restore the potholes and a few years ago, the official count was the trails that provided access to them. again down to 80. Why? The state Legislature authorized funds The potholes acted as repositories for the project in 1985. for all manner of debris. Dust blew in, leaves fell in, and, unfortunately, Pop Bottle Collection. Work began people threw things into them. Larger in June 1987. Workers took down rail- potholes filled with rainwater were ings and erected a protective fence JULY-AUGUST 1988 29 St. Croix Potholes Artifacts recovered from two potholes last\ ear include comb, watch, shoes, porcelain cup, bottles and cans, key case, and, ii center, round "pothole grindstones." around the potholes. As they removed been thoroughly cleaned since the old bridges and trails, they discov- mid-1940s. ered several new potholes buried To remove this incredible pile of under the paved walkways. debris, workers were lowered into the Excavation of the area's two most potholes with a hoist, which they then notable potholes, the "Bottomless Pit" used to lift out loads of mud, rocks, and the "Bake Oven," showed that and litter. A crew of three to five men more than 15 feet of stones, tree worked for several weeks on the proj- branches, pop bottles, and other ect. Finally, on Aug. 4, they hoisted debris had accumulated in the pot- the last load of rocks out of the "Bot- holes since the last time they were tomless Pit. For the first time in 40 cleaned to the bottom. The date of years, the pothole was clean and the that earlier excavation was not bottom was visible, 59 feet 8 inches recorded. However, by dating the below ground level — the world's pennies and the pop bottles found deepest fully excavated pothole! near the bottom, we became reason- Visitors now can see more than 200 ably sure that the potholes had not potholes in the park. Unusual for- 30 THE MINNESOTA VOLUNTEER illations include the "Bake Oven," a "grindstones' from earlier excava- pothole witli a partially collapsed tions were as large as 18 inches in sidewall, which serves as a natural diameter, but those recovered in 1987 entrance for visitors; the Hour- were only an inch or two in diameter. glass, a small pothole shaped as its New trails and bridges were name suggests; an unnamed pair of designed to blend into their sur- potholes that merge several feet roundings. One trail allows visitors to below ground level; and three nat- walk down into the "Bake Oven" along ural arches spanning from 1 to 5 feet. a route closed for more than 30 years. The debris in the potholes yielded For the first time, there is wheelchair lipsticks, sunglasses, combs, flash- access to some major potholes and to bulbs, an old wallet with family pho- Angel Rock, which offers one of the tos still recognizable despite being best views of the St. Croix's rocky buried for several decades in wet mud, gorge. A self-guiding interpretive trail an assortment of pop bottles, two golf with signs explaining the origin of the balls, several marbles, a set of keys, potholes supplements regularly part of a bicycle wheel, and ice tongs. scheduled tours guided by park The most prized items, now dis- naturalists. played in the park's interpretive cen- What does the future hold for ter, were a gold railroad watch and a Interstate's potholes? Despite 90 years folding Kodak Brownie camera, pat- of exploration and excavation, many ented 1909, with film still in it. The of the parks potholes remain undis- greatest curiosity was a porcelain cof- turbed. More than a dozen of the fee cup, miraculously unbroken even largest potholes have never been though it was at the very bottom of a excavated, and as many as 100 more pothole under thousands of pounds of all sizes may be concealed. of rocks. Examination of the uncovered potholes' contents could tell geolo- Grindstones. Some of the rocks gists a great deal about how the holes themselves were curiosities. Smoothly formed. Archaeologists might dis- polished stones, ranging in shape from cover pioneer and Indian artifacts. jelly beans to near-perfect spheres, And who knows? Visitors might have were found by the hundreds in nearly the thrill of seeing even larger and every pothole in the park. Some deeper potholes. • Increase in Minerals Alined in Minnesota, Iron Ore Exported TOTAL VALUE of Minnesota's mineral production in 1987 was $1.3 billion, an increase ot 13 percent over 1986, due largely to improvements in the iron-mining industry. After reaching a low of 24 million tons of iron ore shipped in 1982, the state's exports rose to 32 million tons in 1987 and could rise to 38 million tons in 1988. — DNR News Service JULY-AUGUST 1988 31 .