GEOLOGICAL SCENES FROM THE BLACK HILLS

I recently returned from a fall camping and collecting trip spread out from the high country of Colorado to the Black Hills of South Dakota.  It is such a great time to wander around in the “great outdoors.”  Luckily I returned home to Colorado Springs right before the Great October Blizzard dumped four feet of snow on what was my camping site in Spearfish.

The Pierre Shale (Cretaceous) crops out east of the Black Hills on the plains.  In some localities the concretions in the Pierre produce beautiful cephalopod fossils and crystals of barite and calcite.  This particular concretion gave up a few small bivalves and a barite crystal.

 

These are the famous Fairburn Agate Beds east of the Black Hills along French Creek.  The gravel beds are lag gravels weathered from the Chadron and\or Chamberlain Pass formations (White River Group) while the red colored material is an old (Eocene) tropical soil zone(s).

Cathedral Spires is located along the famous Needles Highway.  The spires developed along vertical joints (see photo below) with weathering in the Precambrian Harney Peak Granite (~1.72 Ga).

No one could visit the Hills without viewing the carved faces of Presidents Washington, Jefferson, Roosevelt and Lincoln on Mt. Rushmore.  The bedrock is the Precambrian Harney Peak Granite, part of a large domed mass of intrusions.

Sylvan Lake at 6,145 feet is usually considered the most beautiful lake in South Dakota.  Again, the Harney Peak Granite..

American bison, buffalo in the vernacular, roam the prairies of Custer State Park in a semi-wild state..

Did you ever wonder where and how South Dakota rivers started.  Now you know the answer!  This ole bull gave us several visits in the Custer State Park Campground at Legion Lake.

Golden Park along French Creek just east of Custer city where men of the George Custer expedition first located gold in August 1874.

Cross sections of several large black tourmaline (schorl) crystals exposed in a pegmatite southwest of Custer city.