Chadron State College
Chadron State College

Interactive Photo Guide - Loop 2

  • Black Hills
  • Hot Springs Mammoth Site
  • Badlands
  Miles Narrative



Begin at junction of Highways 385 and 20 in Chadron, drive West.



Turn North on Highway 385.



Cross the White River.



As you come around the corner look to the left (West). These buttes expose the Chadron and Pierre formations. The grassland below the butte is a typical low-relief landscape eroded into the Pierre Shale. Notice that the landscape between here and the South Dakota state line is rather subdued, without abrupt breaks in the topography.



Entrance to the landfill and recycling center operated by the Solid Waste Agency of Northwestern Nebraska (SWANN). One of the reasons for locating the landfill here was the low permeability of the Pierre Shale that lessens the chance of polluting the groundwater.



The Pierre Shale crops out in the road cut on the Northeast side of the highway just before the electric substation. Here the Pierre contains a few concretions, some with a few fossil remains of ammonites and bivalves.



Cross state line into South Dakota.






Hills on West overlooking the Cheyenne River.



Skull Creek and Mowry shales and Fall River Sandstone.



A flat terrace capped with a well-cemented conglomerate was formed by mineral-rich hot spring water. Spring water circulating through coarse stream gravels turned sediments into hard rock in a relatively short time. This resistant rock now protects this terrace from erosion.



A terrace is a remnant of a former floodplain of a river, left behind when the river cut down through it to a lower level. Often this happens more than once, causing multiple terraces. The older terraces are higher than those formed later. The Cheyenne River has cut at least three sets of terraces at this location.



The silver-gray shale exposed in fairly steep banks is the Cretaceous Mowry Formation.



Cliff on East of highway overlooking the meandering Cheyenne River. The Cretaceous-age Belle Fourche Shale and Greenhorn Limestone are exposed. The resistant Greenhorn forms a prominent ridge, or cuesta, that circles the Black Hills.












Maverick Junction



Turn West on Highway 385/18. Return to Loop 3 if you started here.



Cross the Fall River.



The Cretaceous Fall River Sandstone appears in the cliffs to the West. Many historical buildings in downtown Hot Springs were made with Fall River Sandstone taken from the old quarry on the South side of the highway.



Lakota Formation North of the highway. The Lakota marks the base of the Cretaceous.



The Jurassic Unkpapa Sandstone characteristically takes on a bleached appearance in outcrop. Here it is a distinctive purple-white color.



Outcrop of the Jurassic Sundance Formation.



The Sundance occasionally produces fossil belemnites--cigar shaped internal shells of cephalopods similar to squids.



Bypass Highway 385/18; continue through town or take alternate route to Mammoth Site.



Junction of Highways 385 and 18 in the middle of Hot Springs.



Conglomerate Terrace West of the road in downtown Hot Springs. The waterfall cascading off the cliff of conglomerate is man-made and only runs during the tourist season. This picture was taken just to the right of the waterfall.



3-way stop at Evans Plunge. Evans Plunge is a spa and warm-water swimming pool fed by the hot springs. It has been in operation since 1889.



The Triassic Spearfish Formation is exposed in the hills behind Evans Plunge. The white beds are gypsum, an evaporite mineral that indicates arid conditions at the time of deposition.



Turn East at 3-way stop at Evans Plunge. The road curves North on Highway 385.



Gobbler Pass, Wind Cave National Park.



The Minnekahta Formation is a thin-bedded limestone. Here the rock has been folded as a result of collapse of the underlying Opeche Formation evaporites. Evaporites such as halite (rock salt) and gypsum are weak and soluble in water, and collapse such as this is commonplace.



Edge of Bowman Ridge and exposure of the early Proterozioc Harney Peak Granite. The Harney Peak Granite is the same rock that makes up the Needles and Mt. Rushmore.



Junction 385/89 at Pringle.



Junction of US 385 at Pringle; drive North to Custer. Highway follows a fault named the ,strong>Grand Junction Fault.



Open face hill West side of the highway Pegmatite dike intruding schist (metagraywacke- early Proterozoic age)



The White Elephant pegmatite mine is visible on the side of the mountain east of the highway. The White Elephant has long been the source of high-quality feldspars used for making porcelain. When ground to a powder, coated on a metal substrate and fused at high temperature in a furnace, a highly durable porcelain finish for sinks and bathroom fixtures results.
The photograph at left shows two nearly-vertical pegmatite dikes in the roadcut.






Another pegmatite intrusion East of highway.



Pegmatites are igneous intrusive rocks containing extremely coarse-grained crystals. They commonly form dikes. The reason for large crystal size in pegmatites probably has to do with the presence of water in the magma from which they formed. Water allows ions in the magma to be extremely mobile and to form crystals quickly. Thus, even though a pegmatite may cool relatively rapidly, water allows crystals to grow much larger than would be otherwise possible.



Pegmatites are exploited heavily as rich sources of minerals including quartz, feldspars (to make porcelain), micas (muscovite and biotite), spodumene (a source of lithium), beryl (a lithium source, and sometimes stones of gem quality) and others.



Beecher Rock - East of road. This rock is a sill, a slab-shaped igneous intrusion. The red color is due to oxidation of minerals containing iron. Beecher Rock shows up as a silhouette on the skyline in this image.



An intrusion of pegmatite into Precambrian schist is West of the road.



Custer, SD



Custer; junction of Highways 16, 385 and 89.



Drive North on Highway 89.



Directly to Needles turnaround within Custer State Park.



The vertical granite spires known as the Needles were formed by weathering along joints in the rock. Joints are fractures in rock that occur with regular spacing. This rock has a well-developed set of vertical joints. Water seeping into these fractures splits the rock by frost-wedging, then further breaks down the rock by chemical weathering. Rain water, especially if it is slightly acid, encourages chemical reactions that cause feldspars to turn to clay. Ferromagnesian minerals break down to iron oxides, staining the rock red. These weathering products are much softer than the original granite and they are easily eroded by rain and snowmelt. What is left behind is the rock between the joints, these pinnacles of granite.



Back to Sylvan Lake.



Ranger Station at Custer State Park.



Drive North on Highway 87/89.



Harney Peak, the highest point in the Black Hills and the highest elevation in North America East of the Rockies is visible in the distance.



Weathered pegmatite and schist



The schist that is so common in the central Black Hills is soft, and its well-developed foliation planes lend themselves to rapid weathering. The result is this crumbly material. Here the schist is the country rock (pre-existing rock), intruded by a pegmatite dike.



Junction of Highways 87 and 385.



Highway 385 North to Hill City.



Stop sign in Hill City (across from Super 8 motel and Exxon station).



At stop sign, go East to Forest Service Road #17.



Turn Northwest on Forest Service dirt road #188.



Turn North to Rochford.



Deadwood Formation outcrops West of the highway.



The Deadwood Formation is the lies at the base of the Paleozoic section in this part of the world and preserves the deposits of the first transgression of the sea onto the Precambrian basement. The basal Deadwood is usually sandstone. Because it is so old it is very hard and well cemented, approaching a quartzite.






Junction with US Highway 85.



Turn North toward Lead.



Hillside West of highway.






The layers of rock exposed here consist of an unknown layer, a shale layer which was soft, and a red layer, possibly a banded iron formation.



Banded iron formations, BIFs for short, are iron-rich sedimentary rocks of Precambrian age. They comprise some of the most important iron ore resources in the world. BIFs were formed in seas during Earth's early history, when atmospheric oxygen was just beginning to appear. We suspect that oxygen was present in the atmosphere, because oxygen is probably necessary for iron oxides, such as the hematite in BIFs, to precipitate. Iron in the ferrous state is soluble in water, so is not precipitated. Upon oxidation, however, the iron becomes the insoluble ferric form and precipitates out on the sea floor. Some scientists think that precipitation of BIFs was helped by the activity of primitive organisms, similar to modern blue-green algae, or cyanobacteria.



Lead; junction of US Highways 385 and 85; continue towards Deadwood.



Homestake Mine open pit in Deadwood.



Deadwood to I-90



I-90 East to Rapid City



Rapid City I-90 exit 90 East



I-90 exit 110 at Wall.



I-90 exit at Imperial.



Drive South on Highway 240 to the entrance to Badlands National Park.



Park Entrance



Badlands National Park was created to protect the rare resources of this area, formed by erosion of soft rocks by running water. The term "badlands" was first used by the French explorers of the West who called them "mauvaises terres à traverser" -- bad lands to cross. The term is now applied to any heavily-eroded, gullied landscape.



Most of the rocks you see in Badlands National Park are the Eocene-Oligocene age Chadron and Brule Formations. These formations are not solid rock, but rather soft siltstone, mudstone, and sandstone. Their softness makes them easy to erode resulting in the badlands being one of the most changeable landscapes on Earth.



Running water in the form of sheetwash, or runoff from all surfaces during a rainstorm, gullies and streams. We usually do not see this erosion in action because we usually stay indoors during bad weather. This leads some people to think of wind erosion as an important agent. Actually, erosion by the wind is insignificant in formation of most badlands regions.



Big Badlands turnout



The stratigraphy of the Badlands National Park begins with the Pierre Shale of Upper Cretaceous age. The Pierre is the only marine rock unit in this region. At the top of the Pierre is a highly weathered zone, the brightly-colored Interior Paleosol. Deep weathering to form the Interior took place over the 30 million years of so during which no sedimentary rocks were deposited here.



The Chadron Formation of Eocene and Oligocene age lies above the Interior. The Chadron consists of soft pinkish-gray mudstones and sandstone, the product of streams carrying sediments east from the Rockies and of volcanic ash carried from the far Western Interior by the wind. The volcanic ash has since been devitrified into clays.



The Chadron is overlain by the Brule Formation, Oligocene in age. The Brule has an origin similar to that of the Chadron, but contains more coarse clastic material of stream and river origin.



Overlying the Brule is the Miocene-age Sharps Formation, a sandy unit.



Door Trail turnout



At this stop you can get a good view of clastic dikes, a peculiar phenomenon that is common in the park. They are called dikes, but in reality, no igneous activity is involved.



Clastic dikes are really joints that have been filled with fine-grained clastic material like sand and clay. The filling materials probably were derived from overlying sedimentary rocks that are less well indurated (softer and more crumbly) than the fractured rock.



Visitor Center



Gold, red, & ash layers of the Interior Paleosol exposed on the West side of the road.



The brightly-colored rocks you see at the bottom of these valleys belong to a unit called the Interior Paleosol. A paleosol is an ancient soil. During periods when little deposition or erosion are taking place, weathering of the bedrock occurs, and a soil forms. If this soil becomes buried by other sediments and preserved, it is called a paleosol.



The stratigraphic unit underlying the Chadron Formation here is the Pierre Shale, a marine unit of Late Cretaceous age. After the Pierre Sea drained off the land 65 million years ago, about 30 million years passed before another preserved stratigraphic unit was deposited (the Chadron Formation). The deep weathering that occurred during those 30 million years resulted in the Interior Paleosol.



Seabed Jungle turnout on East side of the road.



Intersection with road to West entrance; Wall and Sage Creek Rim Road.



Turn West on Sage Creek Rim Road.



Antler Butte



Roberts Prairie Dog Town



Contact between two formations on the walls of Beaver Creek.



Far western end of Park.



Junction of Highway 44 and Sage Creek Rim Road; continue West to Rapid City.



Junction in Rapid City of Highways 44, 16, and 79.



Drive South on Highway 79.



Intersection of Highway 16; continue South on Highway 79.



Maverick Junction, continue South.






Route Extension- Hot Springs



Junction of US Highways 385 and 18 in the middle of Hot Springs; turn West.



Conglomerate Terrace. This highly cemented rock is resistant to erosion and forms a caprock, protecting the softer rocks below.



Bypass Highway 385/18, turn West toward the Mammoth Site.



Sundance Formation (Jurassic age).



Road South to Cascade Falls turnoff; continue straight ahead.



Hot Springs Mammoth Site.



The Triassic-age Spearfish Formation forms the distinctive red and tan sandstone around the region. It is also the rock that collapsed into an underground solution cavity to form a sinkhole that trapped scores of mammoths during the Ice Age.



The natural death trap that is the Hot Springs Mammoth Site was discovered in 1978 by workers excavating for a housing development. A backhoe operator recognized the mammoth skull he encountered with his equipment and brought the material to Chadron State College where it was identified by Larry Agenbroad, then professor of Earth science. Within a short time, the developer recognized that the enormous scientific potential of this site was worth saving and the Mammoth Site was formed.



In the enclosed excavation area you can see the mammoths' remains and other evidence for their final moments in the sinkhole. Skulls of nearly 30 mammoths have been found; all are from young males. This suggests that they were members of a "bachelor herd" and were relatively inexperienced with dangers such as this. The sediments clearly exposed in the walls of the excavation also bear evidence of deposition and mammoth activity. Distinct footprints-trace fossils-of mammoths are visible in the walls. Most of the skeletons have also been disturbed, or bioturbated, by mammoths clambering in vain to get out of the pit.



A guided tour through the excavations will give you a first-hand look at one of the most significant fossil localities in North America.



Cascade Falls turnoff - Highway 71 South.



Sheps Canyon.



Sheps Canyon; County Road 71A; turn East.



Outcrop of the following stratigraphic units:



Spearfish Formation, reddish-brown mudstone; the Sundance Formations a greenish-gray sandy mudstone; the Unkpapa Formation, a pure white sandstone, and the Lakota Formation, brownish sandstone.



Return to Highway 71.



Junction of County Road 71A and Highway 7; turn South.



Cascade Springs - breccia pipe in the making below the spring. (See discussion at County Road 18 north of Hot Springs; stop at mile 2.2, below.)



Cascade Falls-formation of a calcareous tufa (locals call this fossilized moss). Picnic area and warm-water swimming hole.



Tufa is the name for a rock that forms near springs as mineral-rich water flows out, cementing together everything it touches. Frequently, tufa contains casts of vegetation such as grass and pond weed that are coated in life by spring-derived minerals.



Return to Hot Springs.



3-way stop next to Evans Plunge; turn North.



County Road 18



Chautauqua Park



Minnekahta Limestone



Conglomerate Terrace



Exposure of the Minnekahta Limestone, the Opeche Shale and the Minnelusa Limestone.






Minnelusa Formation



Opeche Formation



Minnekahta Limestone



Breccia pipe



Breccia is the name for a rock made of broken shards of other rock (breccia means "broken" in Italian). A breccia pipe is an irregular "tube" in the rock that is filled with breccia. The tube was once a passageway for spring water on its way to the surface. As flow died down, the pipe gradually collapsed as pieces of rock making up the walls fell in. Ultimately, the pipe filled entirely and flow stopped, leaving only this remnant.



Return to Hot Springs



End of Loop 2