Wednesday, April 2, 2014


Geologic map of Fall River South Dakota. -----à points out Edgemont, X marks the location of “Igloo.” While Kc indicates outcrops of the Carlile Formation and Kp the Pierre Shale.  Map from Martin and others, 2004.
Fall River County, South Dakota, is located in the extreme southwestern corner of the state and borders Wyoming and Nebraska.  Hot Springs is the county seat and I generally think of the county as the southern end of the Black Hills uplift (Laramide mountain range).  I have collected and explored only a small portion of the county, mostly examining outcrops of Cretaceous rocks around Edgemont.  Today, the village of Edgemont is experiencing a great decline in population and businesses. In the mid- 1960s I visited Edgemont with friends from the University of South Dakota and it was a vibrant and booming town.  The uranium mines (ore from Cretaceous Inyan Kara Group) had a processing plant in town while a neighboring community named Igloo (actually Provo was the town) was the home of Black Hills Ordnance Depot.  This was an interesting place as tens of acres were covered by concrete structures (Igloos) storing army munitions and various varieties of not very nice poisonous gases.  The Depot employed thousands of workers (5000 plus their families) that either lived in housing at the base or in Edgemont. The railroad had a spur line running north to Deadwood and a roundhouse.   As a young man, I distinctly remember all of the activities in the Stockman Bar in “downtown Edgemont” and one year a fairly “wild” Firemen’s Ball on the second floor of a local watering hole.  As late as 1996 the South Dakota Wristwrestling Championship was held at the Stockman.  But alas, the Depot closed, uranium mining went away (although there is talk about new mining near town), logging is essentially non-existent, and I believe the Stockman is closed (at least it looked deserted the last trip through town).  The town has kept a school system with a high school.  I was always impressed with their mascot—the Edgemont Moguls. A mogul is a type of railroad steam engine called a 2-6-0, that is, two leading wheels (no power), six power wheels, and no trailing wheels. 

Munitions storage building, an “igloo.”  Public Domain photo.
The decline of Edgemont mimics many small communities across the Great Plains.  At one time the communities were the centers of life for the surrounding area as people did not have the ways or the monetary means to head to the “big cities” (even Hot Springs in the case of Edgemont).  But then, small farms were no longer profitable, industry  shut down or moved away, the railroads just stopped running (it remains in Edgemont), the Atomic Energy Commission needed less uranium, and the schools consolidate and close  (remains in Edgemont).
Google Map view of a section of the ordnance buildings.
I have seen this decline over and over in my travels across the Great Plains and have first-hand experience with my home town in central Kansas.  The village was mainly a farming community but maintained two grocery stores, a drug store, a café, a pool hall, a couple of gasoline stations, a hardware store, an appliance store, a large grain elevator with a railroad (including passenger service), an undertaker (the hardware guy), a vibrant bank, several repair shops including a small Ford dealer, and a cheese factory.  Saturdays were “big” days in town with the local farmers coming in and buying groceries and gasoline and maybe getting a haircut.  Businesses stayed open “late” and small towns often operated makeshift theaters by projecting movies on to the side of a building.  That kept the children busy and adults were then allowed to complete their transactions.  I graduated from high school in 1961 with 46 school mates (not classmates but 46 total) and perhaps 90% of the local population attended athletic events.  Today virtually everything has closed down except the still vibrant bank, a gasoline station and café/bar.  The town is deserted on Saturday nights.  The high school, after several rounds of consolidation, perhaps has 20 more students than 50 years ago.  Land and taxes are free if you move into town and build a house. The town is not much different than a thousand others.
In recent weeks I have purchased two specimens collected from Fall River County, South Dakota.  One displays nice crystals of calcite that was obviously part of a concretion.  The second is a nice selenite rose.  Both were labeled Carlile Formation near Edgemont.

Selenite Rose from Fall River County, South Dakota.  Maximum width 2.7 cm.

Calcite Crystals from Fall River County, South Dakota.  Width 3.5 cm.

The outcrops in Fall River County are mostly Cretaceous in age (see map) and include a wide range of formations, including the Carlile (Upper Cretaceous in age and sandwiched between the overlying Niobrara Formation and the Greenhorn Formation).  The Carlile is known for its numerous septarian concretions in Fall River County so that seems reasonable.  The selenite rose--I would have suggested the nearby Pierre Shale; however, I will stick to the label.