Historical Marker · No. 393
The Sioux Quartzite
Minnehaha County · South Dakota
Erected by Sertoma Boy Scout Troop 48, John Bradford District, Sioux Council
Geologists now read this rock differently from the bronze. Published dating puts its deposition between about 1,760 and 1,640 million years ago, mostly as sand carried by braided rivers flowing southeast at a gentle grade, with possible marine influence only near the top, and the whole pile runs to about 3,000 meters thick. The Park Service at Pipestone gives about 1.6 billion years and an ancient river. Silica cement makes it harder than steel, 7.5 on the Mohs scale, so it breaks across its sand grains rather than around them.
What the plaque says
The Sioux Quartzite The Sioux Quartzite, deposited more than a billion years ago, is among the oldest rock exposed in South Dakota. The quartzite and associated pipestone deposits were known to white men as early as 1822, but the American Indian used pipestone centuries earlier to make ornaments and utensils. The Sioux Quartzite consists of thick beds of silica-cemented quartz sandstone, the grains of which were deposited and rounded by wave action on the floor of an ancient continental sea. This fact is illustrated by laminations and ripple marks preserved in the quartzite. The density of the rock resulting from cementation and compaction makes it very resistant to erosion as shown by the falls at this site; the Big Sioux River has been flowing in its present course here for about 10,000 years. In Pioneer Days this rock was the principal building and paving material in this area. At the present time its use as an aggregate in concrete construction makes the Sioux Quartzite an important natural resource of Eastern South Dakota. Donated by Sertoma Boy Scout Troop 48, John Bradford District, Sioux Council
Where it stands
43.55629, -96.72423 · Directions
Worth the stop nearby
- Falls Park — 0.3 miThe falls a town company came for in 1856, abandoned in 1862, and tried to make pay with a seven-story quartzite mill that ran for barely two years.