I've driven by that big pit between I-29 and the W. H. Lyon Fairgrounds in Sioux Falls more times than I could count. But I've never seen what's inside.

That “big hole” is the quarry operated by Concrete Materials. The quarry just off Madison Street has been in operation since the 1940s. From the top of the quarry at street level to the bottom of the North Hole is 240 feet. There is also a portion referred to as the 'South Hole' which has been mined since 1980. Parts of the south quarry are at a depth over 325 feet.

In the early 1990s, a tunnel was built under Madison Street to allow the gravel truck traffic to go between the hole without disrupting traffic by continually having to go over Madison Steet.

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Quartzite like that mined in the quarry has been used to construct many historic Sioux Falls buildings.

Quartzite is a metamorphic rock formed from layers of small to medium rounded grains of quartz that have been cemented together by silica, it is so strong that it breaks across the grain instead of around it. Quartzite is between 1.6 and 1.7 billion years old, making it some of the oldest and hardest rocks in the world.

There is a long vein of Sioux Quartzite that basically runs from New Ulm, MN, and extends about 180 miles west to the James River south of Mitchell, SD. The north-south band of outcrops is about 40 miles wide.

If you would like to take an informative guided tour of the I-29 quarry you can Pigeon605.com says Concrete Materials has partnered with Siouxland Heritage Museums to offer guided tours. You can check on dates and availability at siouxlandmuseums.com.

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Look Inside That Big Pit By The Sioux Empire Fairgrounds