There’s a geologic treasure scattered across southeastern South Dakota that has been here longer than our famed petrified forests or the prehistoric fossils painstakingly brushed from the soil. Outcroppings of ultra-hard, 1.6-billion-year-old Sioux quartzite protrude from grassy prairies and riverbanks over 6,000 square miles from the James River eastward into Minnesota and Iowa. The Sioux Quartzite Outcrop Trail includes 10 places in southeastern South Dakota and western Minnesota with significant outcroppings or a close connection with Native American history. The 370-mile loop, which includes stops at Falls Park in Sioux Falls, the Dells of the Big Sioux River in Dell Rapids and Devil’s Gulch in Garretson, is perfect for an overnight excursion.