Spearfish Canyon Through Time

Spearfish Canyon Through Time. Geology of the Black Hills. , The Big Dome , The Black Hills is a dome landform that runs roughly northwest from Hot Springs, South Dakota, to Sundance, Wyoming. It is about 120 miles long by 60 miles wide. It is so large that it is easily visible from outer space. The Black Hills have an ancient inner core of highly deformed and steeply dipping sedimentary (formed by deposits created by water or air) and igneous (formed by volcanic processes) rocks that range from 1.7 to more than 2.5 billion years old., How the Black Hills Formed , The geology of the Black Hills has a long complex history that dates back to some of the earliest known rock formations on earth., The Limestone Plateau and the Racetrack , The central "crystalline" core is surrounded by younger overlying layers of Paleozoic [541 to 252 million years ago (m.y.a.)], Mesozoic (252 to 66 m.y.a.) and Tertiary Period (66 to 2.58 m.y.a.) sediments that dip from the higher inner parts of the uplift. The core is surrounded by a unique ring-like red band of sediments known as the "Red Valley" or "Racetrack" that encircles the Black Hills., Spearfish Canyon , Spearfish Canyon is a unique and spectacular feature of the Black Hills uplift. The Canyon is about an 800 ft. (250 m) deep channel cut through gently dipping sediments of the Western Limestone Plateau., The thinly layered sediments just across the Creek are from some of the oldest (fossil bearing layers) in this region. The massive cliffs above are formed from the Pahasapa or Madison Limestone. This limestone formation contains many caves (including Wind Cave and Jewel Cave). This formation is also a major water-bearing aquifer for much of the upper Midwest., Please respect this special resource and enjoy your visit to the Canyon., Black Hills Gold , The area just east of Spearfish Canyon has produced over 42 million ounces of gold since the precious metal was discovered near the town of Deadwood in 1875., Numerous other mining districts in the Black Hills have produced significant quantities of gold, silver, lithium, beryllium, tin, feldspar and mica minerals., Tertiary Age Intrusive Rocks , Devils Tower and Bear Butte are two examples of Tertiary igneous intrusions that have pushed up through the older rocks in the northern Black Hills. These unique types of intrusions have been known to bear other precious metals and rare elements., Background Photo: Scene Spearfish Canyon near the Mouth of Iron Creek, 1946. , Photo by Jay Higgins, Black Hills National Forest. Courtesy of the Back Hills National Forest Collection, Leland D. Case Library, Black Hills State University.