Mountain Lake Site in southwestern Minnesota preserves a deeply layered archaeological record spanning about 3,000 years of Indigenous presence around a former lake island. Especially important for its Woodland-period remains, the site has yielded some of the oldest evidence of human habitation in present-day Minnesota, including a round dwelling from about 2,100 years ago regarded as the state’s oldest known dwelling and a rare snapshot of Middle Woodland life. Artifacts link much of the site to the Fox Lake focus and later to Oneota occupation. After later Euro-American use and lake drainage, excavations in the 1950s through 1970s confirmed its exceptional value as one of the region’s most revealing precontact sites.