Not long after mountains were uplifted across central Minnesota, sand began to accumulate in braided streams in southwestern Minnesota. These stream deposits of reddish quartz sand grains were eventually consolidated and slightly altered into a very hard rock called quartzite above). The reddish to purple Sioux Quartzite is at the surface near Blue Mound State Park and the Jeffers Petroglyphs in southwestern Minnesota. At the Pipestone National Monument, the soft, red pipestone (catlinite) the Indians favored for carving (below) is a thin claystone layer that is sandwiched between thick layers of quartzite.