History: The Nebraskan Drift; Lyon County, Iowa 

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This file was contributed for use in the USGenWeb Archives by:
Roseanna Mary Zehner  < mslace@netins.net
Janusry, 2003
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The Nebraskan Drift
The bedrock exposures of Northwestern Iowa occur chiefly in the slopes of the Big Sioux 
and the Missouri valleys along the west boundary of the state. Along the west line of 
Plymouth and Northern Woodbury counties, there are many small outcrops, along the 
west line of Southern Sioux County there are a few, and in Lyon County are two or three 
outcrops in the very northwest corner of the state. Away from these valleys only two 
small exposures of bedrock have been reported in Northwestern Iowa. Most of these 
outcrops are in steep valley slopes, evidently gouged away by the glacial action of a later 
(Wisconsin) drift. 
 
Two widely separated divisions of the geologic column are represented by the bedrock 
outcrops in the Big Sioux Valley. The few exposures in Northwestern Lyon County are 
of the Proterozoic, or quart-like rocks, while those of the counties to the south are of 
Cretaceous rocks. In the northwestern corner of Lyon County there are two exposures of 
what is known as the Sioux quartzite. One of these lies near the Minnesota line, and the 
rock stands as a ridge twenty feet high and about a quarter of a mile long. The other 
outcrop is a small valley two miles to the east. These two exposures in Iowa lie on the 
south border of a large area of quartzite, which extends north to Flandreau, South Dakota, 
a distance of forty-five miles, and has its eastern limit at Redstone Ridge, Cottonwood 
County, Minnesota, and its western limit at Mitchell, South Dakota. The rock is well 
exposed at Rowena, South Dakota, just north of the outcrops on the Iowa side, in and 
around Sioux Falls, and at many other places in Eastern South Dakota and Southwestern 
Minnesota. The area within which the Sioux quartzite directly underlies the drift in 
Northwestern Iowa cannot be definitely outlined. The Sioux quartzite and other ancient 
rocks of its geologic age form a basic foundation for Northwestern Iowa. Their upper 
surface dips southward from the outcrops at an altitude of more than 1,400 feet above sea 
level, at Sioux City. 
 
This basic stone of Northwestern Iowa, the Sioux quartzite, is a very hard vitreous rock, 
varying in color from pink to red. It consists of rounded quartz sand grains, so firmly 
cemented with silica that the whole resembles a mass of quartz. 
 
Source: Northwestern Iowa Its History and Traditions 1804-1926 by Arthur F. 
Allen Volume 1.