The rock used at the Shepherd’s Garden for the Ten Commandments, 23rd Psalm, Beatitudes, and the Lord’s Prayer is Sioux Quartzite. Sioux Quartzite is a Proterozoic quartzite over a billion years old. It is found at the intersection of SE South Dakota, SW Minnesota and NW Iowa. It occurs in a deposit 1000 feet thick. The particular rock at the Shepherd’s Garden was quarried by the Jasper Stone Company in Jasper, MN.
Sioux Quartzite is pink or red in color. It is related to other quartzite units in Wisconsin, SE Iowa, Southern Nebraska, north-central New Mexico, and southcentral Arizona. It is not a metamorphic quartzite, but a tightly cemented quartz arenite (sandstone).
Exposures of this hard and scenic red and pink quartzite dot the countryside of SE South Dakota. It was heavily quarried for building stone and used for many prominent structures in Sioux Falls, SD. In Sioux City was used in the construction of the John Pierce House in 1893 (Pierce Street Mansion).
The Sioux Quartzite is extremely resistant to erosion. It was inundated by the Phanerozoic seas during the periods of maximal sea level when the central United States was covered by an ancient sea. For this reason the only geological units to sit atop the Sioux Quartzite are of Cetaceous age (145 to 66 million years ago), deposited when a large portion of North America was covered by the cretaceous interior Seaway.
Many present-day outcrops of Sioux Quartzite were exposed by glacial erosion during our current Quaternary period (2.5 million years to the present). This glacial erosion last occurred in this area 500,000 years ago.