Interstate Park
Interstate Park comprises two adjacent state parks on the Minnesota–Wisconsin border, both named Interstate State Park. They straddle the Dalles of the St. Croix River, a deep basalt gorge with glacial potholes and other rock formations. The Wisconsin park is and the Minnesota park is. The towns of Taylors Falls, Minnesota and St. Croix Falls, Wisconsin are adjacent to the park. Interstate Park is within the Saint Croix National Scenic Riverway and the Ice Age National Scientific Reserve. The western terminus of the Ice Age National Scenic Trail is on the Wisconsin side. On the Minnesota side, two areas contain National Park Service rustic style buildings and structures that are listed on the National Register of Historic Places.
Geology
Rocks or sediment from three short intervals of geologic time, each from three different geological eras, Precambrian, Paleozoic, and Cenozoic, are exposed at the surface within Interstate Park. The oldest strata are of the Keweenawan Supergroup, which is a thick sequence of volcanic and sedimentary strata that fill a segment of the Midcontinent Rift System. During the formation of the Midcontinent Rift System, these strata accumulated about 1.1 billion years ago as a series of basaltic lava flows and alluvial fans filled an ancient rift valley to depth of over. At least ten separate lava flows are exposed within the region of Interstate Park. Since their accumulation, these strata within Interstate Park area have undergone very low to low-grade metamorphism.Paleozoic Era - Cambrian Period
In the Cambrian period of the Paleozoic Era, between 530 and 470 million years ago, the region was covered by a shallow sea which deposited sandstone and siltstone atop the basalt. This epoch of the Cambrian, the Furongian, was originally called the Croixian in North America because the layers exposed in this area were its type locality.Cenozoic Era - Quaternary Period
The presence of older glacial deposits south of the Interstate Park demonstrates that the Laurentide Ice Sheet repeatedly glaciated it and surrounding areas over the Pleistocene Epoch. Within Wisconsin, these older glacial deposits consist of remnants of, highly weathered dark-gray loam till and lake sediment with reversed magnetic polarity and a deeply weathered, pre-Sangamonian Stage, reddish-brown, sandy loam till with normal magnetic polarity. Both the landforms and deposits related to these earlier glaciations have been either eroded or buried by the latest advance of the Laurentide Ice Sheet over this area of the Last Glacial Maximum.The region of Interstate Park was deglaciated sometime between about 19,000 and 14,000 BP calibrated. During this time, the Superior Lobe had retreated from the St. Croix Moraine northeastward to the Thompson Moraine. Between 14,000 and 11,500 BP calibrated, an extensive set of ice marginal channels drained meltwater from the Thompson Moraine by way of the Brule channel into the newly formed St. Croix River.
The glacial landforms and sediments of Interstate Park were largely created during the retreat of the Superior Lobe from this region and periodic outburst flood events from proglacial lakes, e.g. Lake Duluth, since the Last Glacial Maximum. First, the retreat of the Superior lobe into the Lake Superior basin created proglacial lakes. Initially, these lakes consisted of small, proglacial lakes. Later, these lakes coalesced to form a large proglacial lake called glacial Lake Duluth, which was confined to the western Superior basin. The most prominent of multiple lake levels of glacial Lake Duluth is known as the Duluth level. There also was an older epi-Duluth level that lay above the Duluth level. The epi-Duluth level and a smaller precursor proglacial lake, named Lake Nemadji, drained through the higher Moose Lake outlet into the Kettle River and into the St. Croix River. As the Lake Superior Lobe retreated, the Brule outlet opened and the higher Moose Lake was abandoned as a lower Duluth level was quickly established by massive and sudden outflow through the lower Brule outlet and down St. Croix River. The Brule outlet was abandoned when Lake Superior Lobe retreated from the Keweenaw Peninsula and opened lower eastward draining outlets. This caused the Duluth level to drop abruptly to post-Duluth levels and water to cease flowing into lower Brule outlet and down the St. Croix River.
It was during the regional retreat of the Lake Superior Lobe and glacial meltwater flow from deglaciation and glacial Lake Nemadji and Lake Duluth caused the entrenchment of the St. Croix River and the formation of the deep gorge of the St. Croix River of the St. Croix River valley and its famous potholes occurred. In and surrounding Polk County, Minnesota, geomorphic and stratigraphic relationships evidence exists for at least two drainage events.
A strath terrace, known as the Chengwatana surface provides evidence for the occurrence of the first drainage event. The Chengwatana surface is a scoured surface marked by distinct lemniscate landforms; bar-shaped lndforms composed of sand; and a lag layer of cobbles and boulders. This lag layer overlies an unconformity eroded into older glacial till, lake sediment, or bedrock. This surface extends from the lower reaches of the Kettle River valley as far south as Sunrise, Minnesota. The Chengwatana surface likely was cut by water flowing down the Kettle River from the Moose Lake outlet of glacial Lake Nemadji and the Epi-Duluth level of glacial Lake Duluth. The association of the Chengwatana surface with glacial Lake Nemadji and the Epi-Duluth level of glacial Lake Duluth would make it most likely range in age from before 12,100 to about 11,700 BP calibrated.
The deep inner channel, which includes the Dalles, that forms the modern St. Croix River valley was excavated by a second drainage event. This inner channel is incised as a narrower valley cut into, and hence younger than, the Chengwatana surface. This demonstrates that the St. Croix valley is slightly younger than the Kettle River valley and Moose Lake outlet and was cut by water flowing out of the lower and younger Brule outlet of the Duluth level of glacial Lake Duluth. Because the trace of the Chengwatana surface grades to a terrace level higher than the potholes in International State Park, they were eroded by spillway water from Duluth level of glacial Lake Duluth. The association of the Duluth level of glacial Lake Duluth with the second discharge event and creation of the St. Croix valley and the potholes indicates that they were created between 10,800 and 10,600 BP calibrated.
The before-mentioned potholes were created starting with sand and gravel caught in eddies or whirlpools. Within the eddies, the sand and gravel were swirled around with such force that they drilled holes straight down into the rock. Larger rocks caught in the spin would polish the shafts smooth. The Glacial Gardens area on the Minnesota shore contains more than 80 of these glacial potholes, the greatest concentration in the world. When the massive flow of water through the Brule outlet and down the St. Croix River ceased, the potholes became exposed to the air. Dirt, vegetation, and rainwater have collected in them, disguising their true depths. Some have been excavated; one, the Bottomless Pit, is wide and deep, the deepest explored pothole in the world. Other unexcavated potholes in the park are even wider, suggesting that they may be deeper as well.
Weathering has created other rock formations. The Old Man of the Dalles on the Wisconsin shore resembles a human face. Another formation resembling a Maltese cross has been erroneously claimed as the origin of the name St. Croix. A former formation on the Minnesota side called the Devil's Chair looked like a high-backed throne.
Biology
Several habitats are found within the parks. Originally most of the land was forested with large eastern white pines, but was denuded by loggers. Most of the vegetation today is second-growth forest, with some sections dominated by maples and basswoods and others by eastern white pines. Drier areas support oak savanna while wetter areas bear floodplain forest. The driest hilltops even support the brittle prickly pear cactus, the only cactus species native to Wisconsin. Early successional species take hold on the exposed basalt rocks. Over 400 species of ferns and flowering plants have been catalogued in the Wisconsin park.Mammals found in the parks include white-tailed deer, foxes, raccoons, gray squirrels, river otters, minks, skunks, muskrats, and beavers, and 150 species of birds have been identified in the park, of which at least 75 species are known to nest in the area.
Cultural history
The St. Croix River was an important transportation route for Native Americans. Prehistoric tools have been found in the park, but no village sites. The first Europeans to pass through the Dalles were Daniel Greysolon, Sieur du Lhut, and his 1680 expedition, though he made no particular mention of the site Fur traders used the river extensively, and a French fort was located near the Minnesota campground in the early 18th century.Logging era
During the logging era from 1837 to 1898, logs were rafted down the St. Croix River. By 1857 a sawmill was operating near what is now the Minnesota campground, joined in 1867 by a boat-building yard. Both were owned by a leading citizen of Taylors Falls, W.H.C. Folsom, after whom an island in the park is named. The narrow gorge and the sharp turn at Angle Rock caused severe logjams in 1865, 1877, 1883, and 1886. The 1886 St. Croix River log jam is believed to have been the worst in history; at least 150 million board feet of logs were backed up for. Neither dynamite nor steamboats with tow ropes were able to budge the jam. A crew of 175 men working 24 hours a day under electric lights took six weeks to break the jam, during which time several mills downstream went out of business. To control the water flow and prevent further catastrophic jams, the Nevers Dam was built upstream in 1890 in what is now Wild River State Park. The walls of the Dalles rise from 50 to above the river.During this same period, the Dalles of the St. Croix became a popular visitor attraction. Steamboat service to Taylors Falls began in 1838, and a railroad connection was finished in 1880. The catastrophic logjams drew tourists in droves, as many as a thousand a day.