 Several hundred years later , the climate of Minnesota warmed significantly . As large animals such as mammoths became extinct , native people changed their diet . They gathered nuts , berries , and vegetables , and they hunted smaller animals such as deer , bison , and birds . The stone tools found from this era became smaller and more specialized to use these new food sources . They also devised new techniques for catching fish , such as fish hooks , nets , and harpoons . Around 5000 BC , people on the shores of Lake Superior ( in Minnesota and portions of what is now Michigan , Wisconsin , and Canada ) were the first on the continent to begin making metal tools . Pieces of ore with high concentrations of copper were initially pounded into a rough shape , heated to reduce brittleness , pounded again to refine the shape , and reheated . Edges could be made sharp enough to be useful as knives or spear points . 
