The “Three Sisters” outcroppings on the Big Sioux River are part of the Potsdam Formation of rose quartzite that runs at least 2,600 feet deep at the Dell Rapids quarries. The quartzite in this area was used to rebuild many of Dell Rapids’ downtown shops after a catastrophic fire in 1888 that resulted in a City ordinance to required downtown buildings to be of more durable construction.
Image from Dell Rapids
One of the Three Sisters.
