The Shawnee Hills took millions of years to form. The rock formations and cliffs at Garden of the Gods are made of sandstone and are about 320 million years old. Long ago most of Illinois, western Indiana and western Kentucky were covered by a giant inland sea. For millions of years great rivers carried sand and mud to the sea, where it settled along the shoreline. Over time, the weight of the sediments turned them into layers of rock thousands of feet thick. At Garden of the Gods the sediment layers were over 20,000 feet thick or about 4 miles deep. Eventually, a great uplift occurred, raising the inland sea above sea level causing it to fill in with sand and mud. The uplift also fractured the bedrock exposing it to nature’s erosive forces. Since that time, windblown sand, rain and freezing and thawing actions have worn down the layers of sediment creating the beautiful rock formations at Garden of the Gods.
The Garden of the Gods Observation Trail is a 1/4 mile long interpretive trail. It is made of natural flagstone and leads to areas near the bluffs, where there are outstanding views of the Shawnee Hills and the Garden of the Gods Wilderness. Visitors will find many interesting rock formations with names such as Camel Rock, Table Rock and Devil’s Smokestack. The Observation Trail has some short, steep grades and a few steps. However, as a whole, the trail is not tiring. Caution should be used because there are high cliffs in the area.
One interesting feature that has formed from weathering of the sandstone is called liesegang banding, which results in box-shaped and triangular patterns that are dark, reddish swirls or bands in the sandstone. Iron exists as the minerals siderite, magnetite, hematite and some clay minerals that are present in the sandstone. When the sandstone was underground, it was saturated with groundwater mixed with iron. Water fills the pore spaces of the rock formation and comes into contact with these minerals made up of iron. This causes the iron to go into solution. If the rock becomes exposed to air then oxygen is added to the solution and will cause the iron to oxidize and precipitate out along exposed joints in the rock formation. Sometimes color bands result from the different oxidation states of iron and what kind of mineral it is. These bands are also referred to as Liesegang banding. Liesegang band patterns are considered to be secondary sedimentary structures, though they are also found in permeable igneous and metamorphic rocks that have been chemically weathered. Liesegang bands usually cut across layers of stratification and occur in many types of rock, some of which more commonly include sandstone and chert. As you explore the area, you will see some of these bands at other formations and are even a little differently shaped.
To get credit for this, please e-mail or message me the answers to the following questions.
1) What is the height of the top of the rock from the ground?
2) What are 3 of the possible minerals found in iron?
3) Looking at the lighter color of Sandstone in the middle, Why do you think it is smaller in diameter than the rest of the rock?
4) Take a picture of yourself with the sandstone in the background.