Did You Know The Dirt in Mankato Creeks is Blue?

I was recently directed to the Facebook group “Minnesota Naturalists” because there was a very interesting post on there, and boy I did not realize the rabbit hole it would lead me down, but the history is so interesting.

Within the group, there was a post made by a member about the creeks within Mankato. The user explains,

I am from the Mankato area, which got its name when the Dakota word “mahkato” was misspelled. Mankato means blue earth. A lot of people—even people from Mankato—don’t realize that the blue earth we were named for was literally bright blue. Most of it is gone now, because early settlers mistook it for a sign that there was copper in the ground, so it was mined. But there are still deposits of it in a few of the smaller creeks around Mankato.

 

Not only are the photos interesting, but I wanted to know more about why it could be like that and how earlier settlers felt when discovering it. After looking through the comments I decided to do a little research. An analysis done a while ago believes it to be a mineral called Illite. According to blueearthcountyhistory.com “the Blue Earth River and County, and the city of Mankato are all named for the former deposits of bluish-green clay, no longer visible, along the banks of the Blue Earth River."

The stream is said to be named “Makato Osa Watapa” by the “Native Americans of this area, which were the Mdewakanton Tribe of the Dakota Nation, often referred to as the Sioux. [They] called the blue clay “mah-ko-tah” or “mah-kah-to.” (The name of the city Mankato is derived from this word),” explains blueearthchamber.com.

Along with both websites, a Wikipedia page about the Blue Earth River states “the French explorer Pierre-Charles Le Sueur established Fort L'Huillier near the river's mouth in 1700 for the purpose of mining the clay, either in the mistaken belief that the clay contained copper, or as a ruse to secure funding from his patrons for his fur trading activities.”

Unfortunately, because of the history and time, there is very little blue clay dirt, and a lot of people who commented on the original post made this clear, but the author of the post did state that the creek he saw it in is clear “because it drains the lawns of North Ridge in upper North, and the clay is not along the rivers. It is up in the bluffs along small creeks.”

Blueearthchamber.com confirms this by stating “the blue clay is not found around the city of Blue Earth, but in the last few miles of the river course to where it empties into the Minnesota River at Mankato. The clay reportedly is found in small pockets high in the bluffs along the river. This would mean that it occurs in the glacial drift which covers this area except where eroded by the river courses. The small pockets of clay are also reported to be in the soft sandstone.”

All information is credited to the three websites, and the original post made by André Archerd on Facebook.

Photo of Blueearthrivermap by Kmusser / CC BY-SA 2.5(No Changes Made)