Chalkstone Earthcache EarthCache
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The EarthCache site is within a US Corps of Engineers scenic overlook area. Access is by paved roads and an interesting hiking trail leads from this site through canyons that show exposed chalkstone and local terrain and wildlife viewing. The overlook area is closed from 10:00pm to 6:00am.
The EarthCache site shows outcroppings of chalkstone exposed in the late 1950’s during excavations for Gavin’s Point Dam. Chalkrock is basically a form of limestone and is slate grey to cream color. Recently exposed material is usually slate grey while weathered chalkrock becomes a dark cream color. Chalkrock, or chalkstone, is technically called Niobrara Chalk, and it is commonly seen in outcroppings and road cuts in the immediate vicinity of Yankton, SD. Excellent views of exposed chalkrock are seen from the Gavin’s Point damn road pulloffs when you are driving south from the South Dakota side of the Missouri River.
Chalkrock and shale formations of Yankton County are composed of Upper Cretaceous sedimentary rock formations and rest on Precambrian basement rock, possibly Sioux Quartzite. In ascending layered order and decreasing age, the layers of rock that can be exposed are Dakota Formation, Graneros Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation and Pierre Shale. The Niobrara Formation and Pierre Shale layers are exposed in Yankton County in the northeast along Turkey Ridge and in southwest along the Missouri River.
Overlying the chalkrock are deposits of granite materials that may be from the Ogallala Group of rocks deposited by glacial action. The most recent glacial period was more than 12,000 years ago, Age was determined by radiocarbon dating of small bits of wood found in some of those layers. Other granite types of rock may be much, much older.
The significance of chalkrock in the history of the Yankton area is well documented. Uses of the chalkrock include use of a local chalkrock cave as a shelter by early Native Americans, use of chalkrock as a building material, and use of crushed chalkrock as a base cement material or as a light aggregate.
In the very early times of Yankton, Chalkstone Cave was discovered. This cave was used by Native Americans for shelter. Its location was north of the “Chalkstone Hill” road which leads down to Smutty Bear Bottom and Sister’s Grove at the southwest corner of Yankton. Unfortunately, time has erased the cave through erosion and cuts made to establish the road bed. A fine, large example of natural chalkrock still lies at this location along the north side of the road. (Coordinates N42° 52.457, W97° 25.134)
The most obvious example of a quarry for chalkrock lies west of Yankton along Highway 52 as you travel to Lewis and Clark Lake. The quarry is north of a popular local restaurant and the smokestack to the firing ovens of the crushed limestone is still standing. A railroad spur was established to the quarry and operations were constant from 1889 through 1910. Among other applications for “Yankton Cement”, trainloads of material left Yankton to be utilized in the Panama Canal construction. In addition to cement production, the quarried chalkrock was also used in the production of light aggregate (or crushed limestone).
(Coordinates N42° 52.660, W 97° 28.600)
A prominent example of the use of chalkrock as building stone is the Lakeport Church located nine miles west of Yankton on Highway 50 and one-half mile north, one-half mile west on a county gravel road. The church is built from local small granite rocks and chalkrock. The churchyard/cemetery is open and visitors are welcome. The gravel road could be impassable in wet conditions. Most chalkrock buildings have been the victims of severe deterioration over time since it does not weather well. Average life of the typical chalkstone building was 100-150 years. Note that this county gravel road leads through a farm stead; please respect the farmer’s property. (Coordinates N42° 54.847, W97° 34.957)
Please post only your picture with your log message; use my profile e-mail to contact me with the answers to the questions.
Requirements:
1) Post a picture of you or your group with your GPS at the posted coordinates. UPDATE: This is optional.
2) Answer the following questions:
a) What is an estimate of the depth of the exposed chalkrock layers in the bluffs to the west? (Viewed from the cache coordinates.)
b) What is the elevation at the posted coordinates?
c) What is the date of Captain Meriwether Lewis’s speech to early Native Americans?
d) What is the name of the bluff at the posted coordinates?
Permission has been received from the US Army Corps of Engineers for visitors to go to the EarthCache site.
Lewis and Clark Visitor Center
US Army Corps of Engineers
P.O. Box 710
Yankton, SD 57078
Ph: 402-667-7875
Attn: Gary Ledbetter
E-mail: gary.m.ledbetter@usace.army.mil
References:
1) “Geology of Yankton County, South Dakota”, by Gary D. Johnson & Kelli A. McCormick, Ackley-Lawrence Science Center, University of South Dakota, Vermillion, South Dakota (Pgs 2, 10, 11, & 41.)
2) “Yankton: The Way It Was! – Being A Collection Of Historical Columns In The Yankton Daily Press & Dakotan” by Bob Karolevitz, Pine Hill Press, Inc., Freeman, South Dakota 57029. (Pgs 116 & 148)
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