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| Rock City Central |
As an AC/DC fan, anytime that I can work a title from "Dirty Deeds Done Dirt Cheap" into a post, I'm going to take a shot. They are big balls, they are dirty big balls, they are blue balls, they are busted big balls. I don't know that they are the biggest balls of them all, but they are large. The nation is chock full of interesting geological formations, which also tend to have some commercial value. This is true of Rock City Park, a small area (about five football fields long) of about 200 large (up to 30 feet in circumference), primarily ball-shaped concretions in three main groupings.
A similar formation near Clay Center, KS was dynamited for road rock material in 1915, spurring the owner of the current area, William Nisbeth, to preserve this unique feature for future generations.
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| Nadienne provides a size scale for the concretions |
The resulting non-profit organization cares for the area, which has a gift shop, picnic grounds and recently updated outhouses. From May-September a small admission charge is collected ($3 for adults and $0.50 for children under 16 as of 2015). A donation box is also available for after hours visits. If you have kids that love to climb, this is a good place to let them get out and stretch their legs on a trip to or from Colorado along I-70. So many attractions have a "don't touch" policy, but this one seems to encourage interaction with the star features.
Fossilized river bed
Having the world view of a scientist, I find myself constantly "reading" my surroundings, trying to tease out the biological, physical, geographical and geological features/history of the areas I visit. One of the things that leaps out immediately here is the cross-bedding (angled-lines) in the rocks.
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| Concretions showing cross-bedding |
These show that the sand in these concretions was deposited in a river bed. As a river transports sand downriver, the sediments pile up at riffle points until the structure is too tall, and fall over the downstream side of the riffle. The resulting lines of sediment deposition point downwards toward the downstream direction of water flow.
These rivers were active during the Cretaceous at the time of the deposition of the Terra Cotta member of the Dakota Sandstone, roughly 100-112 million years ago. Over time, the sediments piled up to a depth of about a quarter- to a half-mile. The high pressure and the intrusion of minerals like calcite from underlying sediments in groundwater created nucleation points for precipitation of crystals which cemented the sandstone together from the center outwards, creating these ball-shaped structures. Some nucleation points were close enough together that the concretions formed grew together and created long, multilobed rocks. As water and wind eroded the softer surface sediments, the relatively hard concretions emerged in their present form. At several places in the park, it is possible to see ripple marks in concretions that have delaminated (fallen apart).
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| Ripple marks in West Rock City |
Making big ones into smaller ones
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| Blue-gray lichens on sandstone |
The exposed concretions also serve as a great introduction to the process of succession and soilmaking. The exposed concretions are exposed to cycles of freezing, thawing, heating and cooling which widen the cracks in the concretions. The naked rock is also colonized by lichens, a symbiont of fungus and algae. The algae can photosynthesize, making organic molecules from carbon dioxide, water and sunlight. Unfortunately, they lack the ability to hold onto substrate and retain water. The fungus provides an anchor point, and a structure that retains water. The hyphae (threadlike chains of cells) penetrate into the algae, providing water and the algae provide the fungus with organic molecules. The acids released by metabolism breaks down the crystalline structure of the rock that the lichen rests upon. The first organisms to colonize the rock, lichens are part of the group called pioneer species.
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| Plants growing in soil collecting in rock cracks |
As the rock breaks down, and decaying biological matter accumulates, a soil is formed that can hold mosses and then vascular plants in place. The root systems of the vascular plants invade the cracks on the rock, wedging them apart and increasing the rate of breakdown of the rock into soil. Eventually, the concretions break down totally and become buried in the soil that is being made.
A National Natural Landmark
The National Natural Landmark program registers places of natural historical significance, such as this field of concretions. The legislation that produced the Natural Landmark program does not carry the same protections to the site as designation of a National Historic Site, Monument or Park. The agreement is between the landowner (public or private) and the Department of the Interior, and either party may terminate the agreement. There is no necessity of the feature being open to view by the public. In essence the landowner acknowledges that they are caring for a unique feature and will try to maintain its natural features as much as possible. Rock City Park was declared a National Natural Landmark in 1978.
Getting there
Most will approach from I-70. Catch US-81 North for about 10 miles and turn west (left) onto K-18 for 4 miles, then north (right) on K-106 for 5 miles to Ivy Road. Turn left (west) onto Ivy Rd. and follow signs into Rock City Park (about 1 mi).
Waypoint: Latitude 39.0909 N; Longitude 97.736542 W
Street Address: 1051 Ivy Rd., Minneapolis, KS 67467
Further Reading
Roadside America Entry
Kansas Travel Entry
The Giant Concretions of Rock City by Paul Heinrich
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