Sunday, June 10, 2012

BEAR BUTTE; A LACCOLITH ON THE PRAIRIE


BEAR BUTTE, AN EOCENE LACCOLITH NEAR STURGIS, SD

Sturgis, South Dakota, is an interesting small town (~6600 permanent residents) on the northeast flank of the Black Hills.  Most people know the town as the host of an extremely large and rather raucous motorcycle rally held annually in early August.  At this time of the year the population soars to well over a half million temporary residents and non-cyclists avoid the area, and actually the entire Black Hills, at all costs.  At other times of the year stop in for a visit; Exit 30 on I-90.

To a geologist the most interesting aspect of the Sturgis area is Bear Butte sticking up off the prairie a few miles north of town (off SD 79 and in Bear Butte State Park).  Also known as Mato Paha (Lakota), the butte is a sacred to a variety of Native Americans and visitors often see prayer bundles attached to trees, especially along the summit trail.  The Butte is believed by many to be the spot where a creator communicates with her people through vision and prayer.  Each year Native Americans make pilgrimages to the Butte for prayer and spiritual renewal (National Trust for Historic preservation, 2011).  Since it is sacred, during my several visits I chose not to hike the summit trail--just a personal choice.

Bear Butte is an igneous feature termed a laccolith and has domed up the overlying sedimentary rocks. The intrusion is Eocene in age, ~50 Ma, and seems related to other Tertiary intrusions along the flanks of the Black Hills, i.e. Devils Tower and Missouri Buttes in Wyoming, and Crow Peak in the northern Hills.  The rock type comprising Bear Butte is a rather monotonous porphyritic phonolite, a “strange” sort of fine-grained rock (with some larger grains, hence the porphyritic texture) composed mostly of alkali feldspar (orthoclase) and nepheline.  The summit is at 4426 feet and there is a vertical relief of ~1250 feet.
TILTED BEDS OF MADISON LIMESTONE ALONG FLANK OF BEAR BUTTE.
 Most of the Butte is composed of the igneous rock; however, on the east side there is a vertical bed of Minnesula Sandstone and tilted beds of Madison Limestone (Mississippian).  These are remnants of older sedimentary rocks pushed up by the intrusion.

Another interesting aspect of the Park is Bear Butte Lake.  The lake did not exist until 1921 when a wildcat oil well penetrated artesian water, lots of water, in the Madison Limestone.  The water was diverted into the “new” lake.  Today the park’s small campground is located at the lake.
BEAR BUTTE LAKE. 


 If you are interested in western history, there are two other sites worth a visit; both are named for Major General George Gordon Meade.  Meade was the commanding officer of the U.S. Army of the Potomac, receiving his appointment on June 28, 1863, after President Lincoln accepted the resignation of General Joe Hooker.  A few days later the Battle of Gettysburg erupted (July 1-3) and since the U.S. declared a union victory, Meade was given the honor of being the "winning" general.  He seemed never again to be so successful and Lincoln criticized him for not aggressively pursuing Lee.  Meade later served under Lt. General Ulysses Grant for the remainder of the conflict, and in fact, Grant made his headquarters with Meade.  After the War he served the military in various other posts.  Meade's portrait is on the 1890-91 one-thousand dollar Treasury Note, and several geographic localities bear his name. 
1890 UNITED STATES TREASURY NOTE, $1,000, WITH SKETCH OF GENERAL GEORGE MEADE.  SCAN COURTESY OF TOM CHAO'S PAPER MONEY GALLERY. 

George Armstrong Custer suffered his inglorious defeat at the Battle of the Little Bighorn in June 1976.  By the late summer of that year settlers in and around the northern Black Hills had convinced General Phillip Sheridan for the need of U.S. Army troops to protect against the Dakota and Cheyenne Native Americans.  Camp Sturgis was established near Bear Butte in August and was replaced in 1878 by Fort Meade.  The Fort has been continuously garrisoned since that time and today is a Department of Veterans Affairs Hospital and a training center for the South Dakota National Guard. 
FORT MEADE ca. 1888.  BEAR BUTTE IN BACKGROUND.  PHOTO COURTESY OF LIBRARY OF CONGRESS.
The second area to visit is the very tiny Fort Meade National Cemetery, opened in 1878 and closed in 1958 with only 188 burials.  I find the cemetery interesting because of its diversity:  two Medal of Honor recipients and "Lucy, Child, Sioux Indian".  An operating nearby cemetery is Black Hills National Cemetery.
REFERENCES CITED
National Trust for Historic preservation, 2011, 11 Most Endangered Places, Bear Butte: www.preservationnation.org

mike

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