Standing Rock is a sacred site to the Native people of this region and is called "Inyan Bosndata" in the Santee language. The rock is metamorphic gneiss, a combination of quartz, feldspar, and mica, carried here from Ontario, Canada by a glacier more than 14,000 years ago during the Wisconsinan Ice Age, when North Dakota was almost completely covered with glacial ice. The hill beneath Standing Rock is part of the Niobrara Shale Formation and was pushed three miles from the northeast by glacial ice to form a thrust moraine, leaving a cluster of lakes and sloughs in its place. Standing Rock lies in the heart of the Prairie Potholes, a wetland region created as glaciers advanced and retreated across the Dakotas, Montana, Iowa, and the prairie provinces of Canada. These wetlands filter run-off, help maintain water quality, keep heavy metals, pesticides, and other toxins from entering drinking water sources, provide food and habitat for fish and wildlife, and offer natural flood control by storing spring run-off and heavy rainfall until the water sinks into the groundwater or evaporates. French scientist and explorer Joseph Nicollet provided the first written account of Standing Rock in 1839 while mapping the country west of the Mississippi River with his assistant John C Fremont, and he included Standing Rock as a landmark on his map. North Dakota contains more prairie wetlands and produces more ducks than any other state in the contiguous United States, and these wetlands support nearly half of all wildlife species found on the Northern Great Plains, including waterfowl, deer, muskrat, and mink, while also providing recreational benefits for sportsmen, bird watchers, and photographers.