The park is open from sunrise until 10:00 pm.
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In order to log a find on this EarthCache, you are required to send me the answers to the following questions, and post a photo (required):
1. What colors do you see in the Sioux Quartzite cliff surrounding the waterfall, and which colors do you think contain more iron?
2. Based on how hard Quartzite is, do you think the waterfall is causing fast or slow erosion of the underlying Sioux Quartzite?
3. Based on the color and compostion of the two large pieces of Sioux Quartzite at the entrance to the park (near where you parked), do you believe these came from this outcropping of Sioux Quartzite?
4. Post a photo of yourself (your face need not be in the photo), your group, or something that identifies you with the waterfall in the background.
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For thousands of years, the gorge of Red Rock Falls has provided water and shelter from the prairie winds for both animals and people. The gorge and dells is a source of shade trees, recreation, and an opportunity to observe the large cross-sections of the Sioux Quartzite.
You can explore the park by following the trail beside the Red Rock Creek, a small tributary to Mound Creek which passes through the park with a steady flow of water that moves over short steps of rocks called the dells, leading to a 30 foot waterfall. You will first see the layers of Sioux Quartzite, the red to purple colored rock that extends from Sioux Falls, South Dakota, to New Ulm, Minnesota. This is the bedrock of southwestern Minnesota, and is considered to be the hardest rock in the state.
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Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within mountain ranges. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite (iron oxide). Other colors, such as yellow, green, blue and orange, are due to other minerals.
The most prominent bedrock in southwestern Minnesota is comprised of the Sioux Quartzite that extends into South Dakota. The quartzite ranges in color from pink to purple depending on the amount of iron oxides present. The quartzite is derived from quartz sand, the source of which was the erosion of the Penokean Mountains, which were located across central Minnesota and into Wisconsin during Proterozoic time. As the mountain ranges were weathered and eroded, most minerals were broken down into clay minerals and transported away. The resistant quartz grains were transported south and deposited in a braided stream environment.
Cross beds and ripples found in the quartzite indicate the direction of movement of the flowing river systems as the sand grains were being deposited.  Most of the cross beds and ripples indicate a southward direction. Across the border in South Dakota, there are a few locations that have southward dipping cross beds that are found directly beneath northward dipping cross beds. This potentially suggests that the depositional environment found in this location would have been near an ocean shore under the influence of tides. During late-Wisconsin glaciation, glaciers also left their mark on the Sioux Quartzite. Rocks and pebbles embedded in the ice left many glacial striations on exposed quartzite throughout the region.
The Sioux Quartzite has been (and still is) used widely as both dimension stone and aggregate. Modern quarries of Sioux Quartzite can be found as far east as New Ulm and extend west into South Dakota. Many towns in the region have buildings made out of the resistant Sioux Quartzite. Quartzite isn’t used as a building material very much anymore but the demand for quartzite is greater than it’s ever been. Today, the rock is used mainly for asphalt and concrete aggregate. It is an extremely hard stone, nearly as hard as diamond, and it is extremely durable.
Being highly weathering and erosion resistant, the Sioux Quartzite tends to be cliff forming in several locations around the region, as is the case here before you.
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Sources:
Minnesota's Geology, Richard W. Ojakangas and Charles L. Matsch, 1982
Minnesota Rocks & Minerals, Dan R. Lynch and Bob Lynch, 2011
Roadside Geology of Minnesota, Richard W. Ojakangas, 2009
