|
〕 | lat_d = 45 | lat_m = 23 | lat_s = 30 | lat_NS = N | long_d = 92 | long_m = 39 | long_s = 55 | long_EW = W | area_unit = acre | area_imperial = 1628 | area_round = 0 | established = 1895 | management_body = Minnesota Department of Natural Resources, Wisconsin Department of Natural Resources | free_type = Unit of | free = Ice Age National Scientific Reserve | map_locator = Minnesota | map = Minnesota Locator Map with US.PNG | map_caption = Location of Interstate State Park in Minnesota }} 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== 1.1 billion years ago, a series of volcanic eruptions from the Midcontinent Rift System sent at least ten separate lava flows across the region that now includes Interstate Park. These flows hardened into basalt, which fractured at several joints. In the Cambrian period, 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. At the end of the last glacial period 10,000 years ago, torrents of water flowed south from the melting glaciers, carving the St. Croix River Valley. The soft Cambrian sediments were easily eroded into a wide valley, but the hard basalt was resistant to erosion and when it reached the hard basalt floor, the river was channeled into a deep, steep-walled gorge.〔 The river switched courses over time, carving several small ravines. At one stage the flow entered the current channel on the Wisconsin side below the modern gorge, hollowing out an area which is now a backwater lake called Lake O' the Dalles. When the river began carving the main gorge, it intersected an old joint running through the basalt. The water naturally followed this easier path, resulting in the sharp bend in the St. Croix River at Angle Rock.〔Minnesota Department of Natural Resources. Interstate State Park interpretive signage.〕 The walls of the Dalles rise from 50 to above the river. The Glacial St. Croix River carved a series of terraces along its banks. Sand and gravel were occasionally caught in eddies or whirlpools and 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.〔〔State of Minnesota, Department of Natural Resources. ''Interstate State Park''. July 2008. ()〕 The volume of the St. Croix River eventually lessened, exposing many of the potholes 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 ('holy cross' in the French language). A former formation on the Minnesota side called the Devil's Chair looked like a high-backed throne. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Interstate Park」の詳細全文を読む スポンサード リンク
|