“A typical cobble of Sioux Quartzite, about 22 centimeters (9 inches) across. Cobbles and boulders of pink to red Sioux Quartzite are one of the most commonly found rocks in the fields around Lincoln, and eastern Nebraska in general, and are often used as “yard rocks”. The rock is extremely resistant to erosion, and pieces were drug into the area from outcrops in South Dakota by the Quaternary glaciers, about 500,000 years ago. ”