Conor Watkins' Ozark Mountain Experience
Article 6&7
The St. Francois Mountains - Missouri's Hard Rock Core
By Conor Watkins


The St. Francois Mountains - Missouri's Hard Rock Core

Elephant Rocks State Park is one of the most recognized features
in the St. Francois Mountains.

The St. Francois Mountains are a relatively small region of 1.4+ billion year old igneous rocks in southeastern Missouri and are home to some of the most unique natural features in the state.  These small mountains contain Missouri's most ancient of landscapes, many of the highest points in the state, and form the core of the Ozarks.  They are the largest of only three igneous rock exposures in Missouri.  Although a long day trip will allow the visitor to the area to see some of the highlights, the area is best seen over a weekend.  This area is a must see for those who enjoy the outdoors and visitors should pack sunscreen and a camera.

These mountains comprise a relatively remote portion of the state and contain some of the Missouri's least populated counties.  The area is home to the Elephant Rocks, Johnson's Shut-ins, the Black River, Silver Mines, and other popular destinations.  Tourists from other portions of Missouri and Illinois visit the area to seek a retreat on the river or at the many parks and recreation areas scattered throughout the region.  People on weekend escapes fill the area during summer months, bringing appreciated tourism dollars to the isolated area.

Perhaps the most commonly recognized landmarks in the area are Johnson's Shut-ins and Elephant Rocks State Parks.  Johnson's Shut-ins recently made the headlines of area newspapers for several weeks after the December 14, 2005 Taum Sauk Pumped Storage Hydroelectric Power Plant Upper Reservoir failed, resulting in an uncontrolled release of water that severely damaged the park.

General Geology of The Area

The St. Francois Mountains are only a small remnant of ancient igneous activity in Missouri.  It is thought that two continental plates collided during Precambrian times and led to the creation of the original mountains.  Most of the rocks in the area are lighter weight rocks of a granitic composition.  The darker dikes in the area, common in roadcuts, are formed from basaltic minerals and formed when rifting in the area started to split the plates apart about 900 million years ago during the later part of the Precambrian.  These heavier minerals originated deeper in hotter regions earth’s interior.  This rift failed and is no longer active but ancient faults left over from the collision and rift are now thought to form the New Madrid Fault Zone. The fault zone, which was responsible for three of the largest earthquakes in U.S. history during 1811-12, runs through far southeast Missouri and several adjacent states.  This fault zone is still active and has been responsible for some of the largest earthquakes in U.S. history.

Precambrian igneous rocks formed by the same processes present at the St. Francois Mountains are present underneath much of Missouri, including Rolla.  These rocks are simply buried under a thousand feet or more of younger, sedimentary rocks.  The St. Francois Mountains sit at the highest part of the Ozark Dome and all the overlying sedimentary rocks have been eroded.  The Pea Ridge Iron Mine near Sullivan once mined high-grade iron ore from the St. Francois Terrain buried deep in the subsurface.  Economic issues forced the mine to close although its ore is not yet exhausted.

Two other igneous exposures are present in the state outside of the St. Francois Mountains.  The next largest is a series of igneous knobs called the Eminence Knobs located around Eminence, Missouri along the Current and Jacks Fork Rivers.  This is considered an outlier of the St. Francois Terrain.  Another isolated exposure of igneous rock is present at the Decaturville Structure, a strange dome located between Lebanon and Camdenton, MO.  Many believe that this formed when igneous rock was brought to the surface by an asteroid impact several hundred million years ago.

This generalized geologic map of Missouri produced by the Missouri Dept. of Natural Resources
shows the St. Francois Mountains as "Precambrian-Age Bedrock", a map unit represented by a
solid red coloration.  The Eminence Knobs are represented by this same coloration and are
present in Shannon County.

Shut-ins And Johnson's Shut-ins State Park

Although Johnson's Shut-ins is by far the most popular, dozens of other lesser-known shut-ins dot the St. Francois Mountains region.  These unique natural constrictions in the area's rivers formed due to the area's complex geologic history.  The igneous rocks of the St. Francois Mountains were formed over one billion years ago during the Precambrian era by a sequence of violent volcanic eruptions and intrusions of molten rock bodies that cooled and solidified underground but have since been unearthed by erosion.  After their formation, these ancient mountains were exposed to the forces of weathering and erosion.  Creeks and rivers cut valleys across the region, establishing drainage patterns.  After the Precambrian ended, the St. Francois Mountains and the rest of the surrounding Ozarks region dropped below sea level and were blanketed by thick layers of marine sediments, burying the underlying igneous topography.  These sediments became the dolomites, sandstones, shales, and limestones present throughout most of the Ozarks today.

Eventually, the Ozarks and the rest of the St. Francois Montains re-emerged from the sea and erosion took hold yet again.  New creeks and rivers cut a modern drainage pattern without regards to the pre-existing valleys and drainage divides buried beneath the existing land surface.  Sedimentary rocks were stripped from the landscape, exposing the core of the old mountain range as the St. Francois Mountains.  Modern drainages were already well established and did not change course as they cut down to the older, harder igneous rocks below.  Buried igneous bedrock ridges representing topographic highs and drainage divides remain from the ancient terrain.  Since these rocks are more resistant to erosion than than the younger sedimentary rocks that blanket the mountains, modern drainages become contricted as they cut down into these ridges.  These erosion-resistant areas form localized steep, closed in chutes and holes along watercourses locally known as shut-ins.  Modern drainages overlaid atop earlier drainage patterns are known as superimposed drainage patterns.  Much of the St. Francois Mountains region contains such a drainage pattern.   The current St. Francois Mountains generally consist of eroded igneous knobs which form the high points and valleys filled with softer sedimentary rocks. 

No trip to the area is complete without a trip to Johnson’s Shut-ins State Park, the most.  The East Fork of the Black River has carved through fractures in steel hard volcanic rocks to form a natural water park.  The area is home to waterslides, waterfalls, a small underwater shelter, whirlpools, and much more.  The rocks vary in color from pink to black depending on the nature of the volcanic eruption that led to their creation.  The rocks at Johnson’s Shut-ins consist of welded tuffs and ignimbrites, types formed by violent volcanic eruptions.  These extremely hard rocks formed when clouds of hot volcanic ash roared down a mountainside and settled to the ground, becoming melted and "welded" together by residual heat.  During warm weather, most visitors to Johnson's Shut-ins State Park spend a few hours swimming at in the shut-ins.  High cliffs and deep water offer the opportunity for a good cliff jump.  Although this practice is prohibited and unsafe if practiced carelessly, it still occurs within the park.  Recently, park rangers have been conducting a more stringent enforcement of the "no jumping" policy and violators are now subject to a stiff fine of up to $500.

The river remains relatively cool and very clear even on the hottest days. For this reason, it is important to get to the park early on hot days.  Anyone not at the park by around 10:00 a.m. on a hot day may have to wait in line for hours in order to get in as only a certain number of cars are allowed in at one time.  If taking a day trip to the area, make sure to make this the first stop.  The park offers camping, fishing, climbing (with permits only), picnic areas, a small convenience store, hiking trails, and swimming.  The park is currently closed to the general public and will remain so until further notice due to damage caused by the failure of the AmerenUE Taum Sauk Pumped Storage Hydroelectric Power Plant's Upper Reservoir (see below).

Johnsons-Shut-ins is one of Missouri's most popular swimming holes on hot summer days.

The Taum Sauk Pumped Storage Hydroelectric Power Plant

Since the early 1960's, the Taum Sauk Pumped Storage Hydroelectric Power Plant's Upper Reservoir has sat high above Johnson's Shut-ins State Park atop Proffit Mountain.  Taum Sauk Mountain, the plant's namesake and the highest point in Missouri, sits about five miles to the east of the facility.  Although it is only a short distance away from Johnson's shut-ins, views of the facility are blocked by the tall ridge on the east side of the park.  This plant was constructed by Union Electric (now AmerenUE) as a way of storing electrical power and began operations in 1963.  The plant consists of a lower reservoir situated along the East Fork of the Black River just downstream of Johnson's Shut-ins and the upper reservoir sitting 800 feet higher.  The lower reservoir was created by constructing a concrete dam across the East Fork.  The upper reservoir was constructed by blasting off the top of Proffit Mountain and forming the blasted material into a kidney-shaped earth and rock dike approximately 80 feet in height, creating a lake resembling a large bathtub built atop the mountain.  A 10 foot tall concrete parapet wall was placed on top of the dike to increase storage capacity.  The inside of this reservoir was originally lined with concrete and later given an additional plastic HDPE liner in 2004 to reduce leakage.  When filled, it holds 1.5 billion gallons (4,600 acre-feet) of water.

The kidney-shaped upper reservoir at the Taum Sauk Pumped Storage Hydroelectric Power Plant
holds 1.5 billion gallons of water when filled.
  Source: Ameren Media Center Photos (

Additional photos are available at the Ameren Media Center link.

The two reservoirs are connected by a 7,000 foot long, 25 foot diameter tunnel through Proffit Mountain.  A powerhouse containing two reversible pump-turbine units uses electricity to pump water uphill during periods of low electrical demand (usually at night) where it is stored as gravitational potential energy in the upper reservoir.  During periods of high electrical demand (usually during the day), the flow of water is reversed and a maximum of 440 megawatts of electricity can be generated to provide peaking power.  The plant can be thought of as a gigantic battery that is discharged and recharged on a daily basis.  Although the lower reservoir is continuously filled by water from the East Fork, the upper reservoir recieves its only water input from the pumps and very minor contribution from precipitation falling directly into the basin. 

As with any energy conversion, this process isn't 100% efficient and electrical energy is actually lost during operation of the facility.  Those unfamiliar with the system often question why anyone would spend $50 million (1963 dollars) on a power plant that uses more electricity than is generated.  The power plant is just one part of a highly complex electrical grid and uses power generated by coal, nuclear, and other hydroelectric plants to fill its upper reservoir.  In order to maintain the stability of the electrical grid, coal and nuclear power plants must be operated at a relatively constant power output.  This means that in order to keep up with high demands during the day, those same power levels must also be maintained at night, resulting in the complete loss of this excess night time power.  The Taum Sauk Plant was constructed to capture and store this power for use the next day, resulting in the ability to run coal and nuclear plants at a slightly lower power output, actually saving electricity and natural resources.  In addition, this type of power plant can respond to rapidly fluctuating power demands and provides a near-instant response during such periods.  Instead of the hours required to change the output of a coal or nuclear plant, this system can adjust in a matter of a minute or so.  The upper reservoir is filled at night with inexpensive off-peak power.  Power generated during the day sells for a greater cost, allowing for the plant to be quite profitable.  Upgrades and enhancements to the facilities increased the efficiency of the plant to about 71% by October 2005.

The power plant is both an interesting geologic and engineering feature.  A sharp unconformity of sedimentary Cambrian-age (~500 million years old) dolomite atop Precambrian igneous rhyolites was unearthed during excavation around the powerhouse area.  This location shows what is known as the Great Unconformity in which approximately one billion years the geologic record is missing over much of North America.  This is a unique and relatively accessible view of this feature.  Other famous locations where the Great Unconformity may be viewed include less accessible and far away locations such as the bottom of the Grand Canyon.  This exposure has been viewed by students and geology buffs from all around.  The exact processes that occured during this missing one billion years is not known.  Much erosion took place, establishing the ancient drainage patterns that have played a major role in the formation of the area's shut-ins.

An onsite indoor/outdoor museum is provided by AmerenUE to highlight the area's natural and human history.  Mineral resources of the state along with Indian artifacts and other archeology are featured.

On September 26th, 2005, the Institute of Electrical and Electronics Engineers (IEEE) honored the plant by declaring it an engineering 'milestone' and joined the ranks of less than 70 other projects that have recieved the award worldwide.  This project was honored with this award due several pioneering features.  It was the first and largest (at the time) pure pumped storage project in North America, features high capacity pump-turbine units, and can generate power during a complete blackout of the power grid, allowing it to help restart the entire system.  It can be operated remotely from St. Louis, the Osage Power Plant at Bagnell Dam, or run completely automatically without any human control.

The Upper Reservoir Failure

Just one day before the facility won the prestigious IEEE award, the first sign of problems appeared at the upper reservoir.  It was a Sunday and employees were usually not onsite but were getting ready for the award ceremony to be held the following day.  Water and wind whipped waves were observed pouring over the northwest wall of the reservoir in an event described as "Niagara Falls."  Plant operators acted quickly by turning off the pumps and switching on the generators to lower the water level in the reservoir.  Something appeared to be wrong with the automatic water level gaging system in the upper reservoir and it was allowing the pumps to fill the reservoir beyond its desired level.  New water level sensors installed during the placement of the HDPE liner had started acting up.  Plant operators warned that continued overtopping of the reservoir wall would lead to a erosion of the dike, leading to a catastrophic failure.  They warned "The dam would severely erode and cause eventual failure of the dam.  Those kinds of headlines we don't need."  Supervisors recommended lowering the maximum level of the reservoir by three feet to add a cushion to their safety margins.   

The reservoir had finished a nightly refill just before 5:30 a.m. on December 14, 2005.  A warning alarm signaling a failure sounded 12 minutes later when water level sensors indicated that the reservoir was empty.  In these 12 minutes, 1.5 billion gallons of water roared down an un-named tributary of the East Fork and straight towards the upstream portion of Johnson's Shut-ins State Park.  Although the peak flow of the flood isn't known and may or may not be uncovered by the official investigation, the average flow was 280,000 cubic feet per second, larger than the average flow of the Mississippi River just upstream from its confluence with the Ohio River!  The peak flow was likely larger.

The flow incorporated concrete and steel rebar from the parapet wall and reservoir liner, soil and rock from the reservoir dike, and some of the HPDE liner in what became a turbid and dense slurry of material known as a debris flow.  The high density of the flow gave it a greater destructive power than clear water would have had alone.  It stripped additional soil, rock, and trees from the upper slopes of Proffit Moutain, exposing the bare bedrock.  A large hydraulic jump and scour hole at least 20 feet deep formed when the gradient (steepness) of the slope dropped at the base of the mountain.  At this point, the flow slowed and began depositing materials into a boulder-choked stream.  Large boulders and sections of concrete were carried far downstream with some making it all the way to Johnson's Shut-ins State Park.  The momentum of the flow allowed it to bank high around turns, scouring the outside edges of the ravine while leaving the insides of curves unscathed.

A large scour hole was formed by the hydraulic jump marking the transition between
the upper steep portion and the lower, more gradual slopes of Proffit Mountain.  The
hole is at least 20 feet deep and was likely much larger before the diminishing flows
near the end of the flood filled much of it with debris.
This photo was taken by author during March 2, 2006 geologic field trip through the entire scour
zone with AmerenUE consulting geologist and engineer from MACTEC.

This large section of the concrete parapet wall was carried down the upper slope of
Proffit Mountain by the destructive flow.
This photo was taken by author during March 2, 2006 geologic field trip through the entire scour
zone with AmerenUE consulting geologist and engineer from MACTEC.

Geology once buried beneath a secretive cover of vegetation and soil was stripped clean by the violent flow.  Weathering surfaces, both ancient and modern, were exposed.  Weathering features included a mosaic of saprolite (igneous rocks weathered in place to a clay like soil) that had weathered along an ancient fracture pattern became visible.  Although this material more resembled soil than rock, the original fabric and fracture pattern are still present. An ancient volcanic agglomerate, or breccia was also visible, indicating that violent events had taken place at this site well over a billion years ago.  The newly exposed geology at the site will likely be the focus of publications and field trips for years to come.

A highly weathered diabase dike cutting across the upper slopes of Proffit Mountain was stripped clear of its soil
and vegetation cover, exposing a mosaic of saprolite.  Although this material has weathered to a soft soil like material,
the original fracture patterns of the rock are visible (left).  Several remnant core stones are present within this mass (right).
Concentric weathering rings are clearly visible surrounding the stone clear to the original fractures.
This photo was taken by author during March 2, 2006 geologic field trip through the entire scour
zone with AmerenUE consulting geologist and engineer from MACTEC.

The upper slopes of Proffit Mountain were stripped down to their ancient igneous bedrock,
exposing features never seen before.  A volcanic agglomerate is shown here.
This photo was taken by author during March 2, 2006 geologic field trip through the entire scour
zone with AmerenUE consulting geologist and engineer from MACTEC.

The mass flowed from the steep, unnamed ravine into the broad flat valley of the East Fork at the upstream end of Johnson’s Shut-ins State Park where it scoured a large hole into the bed of the river.  The flow lost much of its energy and dropped the larger, denser material including large boulders, pieces of concrete, and steel rebar into the East Fork and its valley just upstream from the gorge at Johnson’s Shut-ins, forming a rubbly debris dam.  The site was filled with boulders and twisted masses of steel rebar resembling spaghetti.  The scour hole and debris dam combined forces to create a small lake where the torrent of water entered the valley.  The flow swirled in a large eddy, taking many trees and other lighter debris upstream along the valley of the East Fork where they were deposited north of Hwy N.

The home of park superintendent Jerry Toops and his family was directly in the path of the flow.  Jerry awoke to his wife screaming about a sound she though was a tornado heading their way.  He described hearing something sounding like a combination of multiple trains and the F-14’s that commonly practice over the park.  Jerry was aware of the reservoir and realized it had probably failed, placing his family in grave danger.  He began to get up to gather his family but the wall of water and debris hit the house as he was getting out of bed, ripping it off the foundation.  The family was carried upstream across Hwy N to private property where they were deposited throughout a large field north of the park.  The family’s personal possessions, their two vehicles, and portions of the demolished house were scattered throughout the same area.  The family of five (including three young children) suffered injuries but all survived and have since been released from the hospital.  Had the family’s house had been located a few hundred feet to the south, they would have been incorporated in a portion of the flow that went directly towards the rugged gorge of Johnson’s Shut-ins and almost certainly killed.  If they had been located closer to the mouth of the tributary, they would have been exposed to a more energetic and violent portion of the flow.

Several motorists including a trucker carrying lead/zinc ore from mines in the area were struck by the wave.  All were able to get onto the roofs of their vehicles and survived the flood uninjured.  The trucker ended up helping rescue the Toops family.

The flow released during the failure stripped the upper slopes of Proffit Mountain down to bare
bedrock.  This picture shows the ~600 foot wide break, stripped area of Proffit Mountain, and the
upper portions of the lower scour zone.
This photo was taken by author during March 2, 2006 geologic field trip through the entire scour
zone with AmerenUE consulting geologist and engineer from MACTEC.

The flow lost more energy and deposited additional lighter debris including pieces of plastic sheeting once used to line the reservoir and the thousands of trees stripped from the side of Proffit Mountain throughout the valley upstream of Johnson’s Shut-ins.  The muddy flow reversed course and began moving downstream towards the rocky gorge of rhyolitic tuff at Johnson’s Shut-ins.  The narrowing of the shut-ins restricted the flow, backing up water in the upstream portions of the park.  The slowing of the flood allowed mud, leaves, trees, rock, concrete, and other debris to be deposited.  The campground and parking lot areas at the park were stripped of most trees and coated with a thick layer of mud and debris.  Most picnic areas, restrooms, kiosks, and the park’s water treatment plant were severely damaged or destroyed while the park shower house and store sat near the high water line and experienced lesser damage.  Rangers at the park believe that the thick mud of the flow helped seal these buildings from the flow, preventing greater water damage to their interiors.



The campground at Johnson's Shut-ins State Park was essentially destroyed by the surging floodwaters.
Debris, including trees, boulders, concrete, steel rebar, and plastic lining from the reservoir were washed down
Proffit Mountain and into the campground.  Most trees and facilities in the campground sustained damage due to the
force of the water and debris.  Had there been people staying at the campground, they would have likely not realized
the severity of the situation until it was too late to escape.  Had this occurred on a busy summer weekend such as
Memorial Day or July 4, there would have likely been a large loss of life.
These picture was taken by the author as part of a UMR-USGS reconnaissance
of the damaged area on Dec 15, 2005, the day after the flood.

The flow then roared towards the shut-ins themselves, covering the path's to the feature with debris and a thick layer of mud.  The boardwalks supporting the path were damaged and covered with debris although the underlying structure consists of welded steel that withstood the flow.  The flood ripped through the narrow gorge of the shut-ins with such a great force that most debris was simply carried on through with the exception of the lower shut-in.  That large hole, which was once tens of feet deep, was filled in with debris.  Trees lining the margins of the gorge were bent over and splintered.  Other trees and debris were deposited about 40 feet above the bottom of the gorge at the top of the shear rhyolite cliffs at betweem the upper and lower shut-ins.  Cedar trees in the path of the flood were shredded, releasing a pleasant aromatic odor that lingered for days after the flood.

Trees from the flood were deposited 40 feet above the river on the left bluff along the chute
separating the upper and lower shut-ins.  Had there been people swimming in the shut-ins
when this occured, they would not have had time to get away once they realized something
was seriously wrong.  This picture was taken by the author as part of a UMR-USGS reconnaissance
of the damaged area on Dec 15, 2005, the day after the flood.

The trail to the shut-ins was covered by debris and a thick layer of mud from the flood (left) while the boardwalks
sustained damage and accumulated debris (right).
These picture was taken by the author as part of a UMR-USGS reconnaissance
of the damaged area on Dec 15, 2005, the day after the flood.

The hard rocks of the shut-ins have survived thousands of years of natural flooding and came through this flood in remarkable condition.  Besides the brown muddy water and some extra debris, the shut-ins looked unchanged the day after the flood came roaring through.



Besides the muddy water and some debris left from the flood, Johnson's Shut-ins itself
came through the flood very well.  The steel hard rocks survived this flood as
they have survived thousands of years of natural flooding.  These pictures were taken
by the author as part of a UMR-USGS reconnaissance of the damaged area on Dec 15, 2005,
the day after the flood.

The rocky gorge at Johnson’s Shut-ins restricted the flood of water from the reservoir breach and dissipated much of its destructive energy, sparing the valley downstream from the shut-ins the damage experienced upstream of the gorge.  Water passing through the shut-ins flowed a short distance into the Lower Taum Sauk Reservoir.  Much of the water in this lake had been pumped uphill earlier in the morning as the upper reservoir was being filled, leaving it partially empty.  The lower reservoir absorbed much of the flood and turned a muddy brown.  The lower dam, essentially an ogee crested spillway weir, is constructed of concrete and designed to be overtopped.  Although some of the muddy brown water flowed over the crest, the dam sustained no structural damage and held back much of the flood and debris.  This caused a small rise in the level of the river downstream in Lesterville but it remained well within its banks.  These flows caused only minor damage along its course to Clearwater Lake farther downstream but turned the clear waters of the Black River brown for some time.

The lower taum sauk reservoir held back much of the flood and prevented greater damage downstream.
This photo of the lower dam was taken the day after the failure and murky brown water and floating
debris filled the reservoir.

Although there were injuries and damaged property due to the flood, there were no deaths.  Had the reservoir failed in another location or at another time of the year, the story could have been far worse.  The campground at Johnson’s Shut-ins is often filled to capacity during the warm summer months.  If the flood had occurred during the early morning hours of a July 4 or Memorial Day weekend, hundreds of sleeping campers would have no time to escape the surging floodwaters that obliterated the campground and then roared through the rugged gorge at the shut-ins.  Luckily there were no campers at the park in mid-December as the campground was completely destroyed by this violent event.

Although the cause of the failure is still officially under investigation, it appears that the reservoir was overtopped in at least three locations.  This overtopping scoured the foundation materials supporting the concrete parapet wall and one other location appears to have nearly failured during the overtopping event.  As with the Sept. 25th overtopping, it appears that sensors failed to accurately detect the water level, allowing water to be pumped over the top.  Perhaps the sensors had pulled loose from the bottom of the reservoir and weren't reading the full depth of the reservoir.  AmerenUE accepted full responsibility for the failure later that day and has been working with the Missouri Department of Natural Resources to restore Johnson's Shut-ins State Park, the Black River, lower reservoir, and surrounding area.  Both Johnson's Shut-ins State Park and AmerenUE's Taum Sauk Facility have been closed to the public since the failure of the reservoir.  The Missouri Department of Natural Resources and AmerenUE hope to have limited day-use services available at the park by summer although restrooms, camping, drinking water, and other amenities won't be available until the later.  The Taum Sauk Facility will likely be closed to the public throughout the investigation and may not re-open if it is decided not to repair the reservoir and resume operations.

This map has outlined main areas that sustained major flooding and damage due to the failure of the
Upper Taum Sauk Reservoir in blue.  The map was created by the USGS Mid-Continent Geographic
Science Center in Rolla, MO soon after the flood.  More maps, photos, and information on the failure
from the USGS-MCGSC may be found at

Missouri's Only Silver Mine

The Silver Mines Recreation area of the Mark Twain National Forest is another interesting attraction withing the region.  It is a good alternative for those turned away from an overcrowded Johnson’s Shut-ins.  The Silver Mines area offers interesting hiking trails, a campground, and has its own shut-ins, which are available for swimming and fishing.  This shut-in is made in granite, not the welded tuff present at Johnson's Shut-ins.  The rocks more resemble the rounded boulders at Elephant Rocks than the angular rocks at Johnson’s Shut-ins.  Igneous dikes made from diabase, a rock consisting of heavier, more iron rich minerals are present at this site.  These structures appear as dark linear structures running through the pinkish rock and the best example is present near the old dam along the river.

The Silver Mines area was once mined for silver and tungsten ore, hence the name.  It is the only area in Missouri that was ever mined primarily for silver ore.  At least two abandoned mines are present on the site.  One of these mines is along a trail, but is gated due to the instability of its roof.  An old and dilapidated dam made of local granite, a leftover from the mining days, is also present at the site.  The Amidon Natural Area, Stout’s Creek, and many other locations in the area contain natural shut-ins worth visiting.  The Tiemann Shut-in/Millstream Gardens area, not far upstream from Silver Mines, offers the roughest whitewater in the state and it is a tradition to hold kayak races there in the spring, usually March and April.  This scenic shut-in is a narrow restriction in the river and well worth a visit.  For more information on the races, visit

Elephant Rocks State Park

Elephant Rocks State Park is another highlight of the St. Francois Mountains region and offers some unique scenery seen nowhere else in Missouri.  The highlight of the area are its large pink granite boulders that have weathered to rounded shapes that resemble elephants when your imagination is used.  Granites form when magma (molten rock below the surface) intrudes into the subsurface and cools slowly, forming rock bodies with a course grained texture deep in the earth.  Chemically, granites are similar to rhyolites but differ in the fact that their grain size is much larger.  These granites were eventually exposed at the surface by a combination of uplift and erosion.  Stresses locked into the granite by its deep burial were released as it moved closer to the surface, causing it to fracture.  These fractures provided for zones that preferentially weathered, forming the elephant rocks.  Some rocks are about the size of an elephant while others are much larger.  This park offers a guided hiking trail that is wheelchair accessible and offers interpretive signs in Braille.   The trail takes the hiker through the elephant rocks.  The largest of the elephant rocks is hundreds of feet long and serves as a platform offering excellent views of the surrounding area.  Other enormous rocks are ‘balanced’ on top.  One section of the elephant rocks resembles a rock maze with tight passages and steep walls.  One will notice that the maze tends to have many parallel passages which were inherited from the original fracture pattern.

The linear traces of the fracturing within the granite has led to this pattern
or parallel slots and fins in within the granites at Elephant Rocks State Park.

Elephant Rocks State Park is home to a handicapped accessible trail that leads the visitor
through the granite boulders for which the park is famous.

Excellent exposures of granite rock are present at Elephant Rocks and areas within the park were once quarried for this resource.  Granite from this supplied building and facing stone to St. Louis. The cobblestones on the St. Louis Riverfront are granite from the St. Francois Mountains area.  The controversial Millennium Arch on UMR’s campus is also made from red Missouri granite much like the kind at Elephant Rocks. Quarrying began within what is now Elephant Rocks in 1869 and rock was transported via narrow gauge railroad.   The town of Graniteville was orginally names Granite Quarries until it was renamed in 1876.  A new owner purchased the quarry an 1182, greatly expanding the operation.  Railroads were converted to standard gauge rail and the surrounding town grea to a population of 700.  Although the quarry produced dimension stone for buildings, the main product was pavers for city streets.  The demand for pavers declined in the 1930's and the mine began to shrink.  Graniteville is now only a shadow of its former size although the mine still operates, mainly producing dimension stone and monuments for cemetaries, etc. at its quarry close to Elephant Rocks in Graniteville.

A massive wet saw cutting granite dimension stone at the Missouri Red Granite Quarry
in Graniteville.

The 120 acres composing Elephant Rocks was purchased and donated to the state by John Stafford Brown in 1966.  Brown served as the chief geologist for the St. Joseph Mining Lead Company and led the group who discovered the Viburnum Trend in 1947.  The Viburnum Trend is locations in Missouri and is one of the world's largest reserves of lead.  He was also a graduate of the Missouri School of Mines (now the University of Missouri - Rolla).  The park is one of Missouri's most popular state parks and sees around a half million visitors per year.

The pit from an the old granite quarry is located along the trail near the back of the park.

The Devil's Honeycomb

The Hughes Mountain State Natural Area provides an excellent example of columnar jointing in igneous rhyolite, a rare phenomenon.  Other examples of this columnar jointing are common in basalt but not rhyolite.  Columnar jointing is common in basalts at Devil’s Tower in Wyoming, Devil’s Post Pile in California, and in the Western Grand Canyon.  As with some of its western relatives, this feature includes the devil in its name, Devil’s Honeycomb.  The strange geometric shapes somewhat resemble a honeycomb, hence the name.  Igneous glades in the area are home to a few hardy plants and animals but much of the surface is honeycombed bedrock, a surface inhospitable to more life.  These strange geometric formations were created when the volcanic ryholite intruded into the shallow subsurface, cooled, and contracted over 1.4 billion years ago.  This phenomenon is similar to the cracking of mud as it dries and contracts.

The Devil's Honeycomb is the highlight of the Hughes Mountain Conservation Area.

Missouri's Highest Point

At 1772 feet, Taum Sauk Mountain is the highest point in Missouri and is included in Taum Sauk State Park. Unlike the high mountains of the western U.S., the trail to its summit is wheelchair accessible.  A fire tower at the park offers excellent views of the surrounding countryside even though the shelter at the very top is closed to visitors.  The actual summit of the mountain is marked with a small marker stating the elevation and date of the measurement.  The highest point in Missouri is only a couple hundred yards from the nearest parking lot and is an easy hike on a paved trail.  The trails at both Taum Sauk and Johnson’s Shut-ins connect to the extensive Ozark Trail, a trail that has become known as one of the premier backpacking trails in Missouri.  For more information on the trail, see  Although Taum Sauk State Park wasn't damaged by the failure of the Upper Taum Sauk Reservoir, portions of the Ozark Trail near Johnson's Shut-ins remain closed.

Mina Sauk Falls, Missouri’s highest waterfall, is also located in Taum Sauk State Park a little over one mile from the parking lot. Although impressive after a rain, there isn’t much flowing over these falls during dry periods.  Mina Sauk Falls is named for an Indian legend about two lovers from opposing tribes.  One lover was thrown over the edge by Mina Sauk’s tribe.  It is said that Mina Sauk then jumped herself.  The falls were said to have been created to wash the area of blood.  The trail to these falls is much rougher and decent boota/shoes should be worn.  Devil’s Toll Gate, a large rock fissure through which the trail passes, it present farther down the trail.  The rock present in this area is a classic example of porphyritic rhyolite, a volcanic rock formed by relatively quiet lava flows on the earth’s surface.  These rocks are fine grained but a porphyritic and contain courser mineral crystals that formed before the rock was erupted.  Even though they are 1.4+ billion year old, these rocks still preserve flow patterns from the movement of the original lava flows.

Getting There And Additional Stops Along The Way

From Rolla, head east on I-44 to the St. James exit.  Turn right on Hwy 8 and follow it for about 60 miles to Potosi.  From Potosi, turn right (south) on Hwy 21.  To visit Hughes Mountain and Devil’s Honeycomb, follow Hwy 21 eleven miles to Hwy M on the left.  Turn left and follow Hwy M for 5 miles to Cedar Creek Rd.  Turn right here and the parking lot will appear after less than a mile.

To get to Elephant Rocks State Park, Continue on Hwy 21 south through the town of Caledonia.  Soon after Caledonia, expect to see signs for Elephant Rocks on the left. If it is a warm day, it is suggested that the visitor continue on and visit Johnson’s Shut-ins first.  Soon after Elephant Rocks, Hwy N will be off to the right.  Take this road about 10 miles to the entrace at Johnson’s Shut-ins, which will be on the left.

From the shut-ins, continue to head south on Hwy N towards the town of Lesterville.  Turn left on Hwy 49/21.  For a good taste of southern Ozark culture, a stop for lunch at Lenny’s, Not Denny’s, Quick Stop is suggested.  This small convenience store serves excellent sub sandwiches and burgers.  Lenny’s specializes in packing ‘river ready’ sandwiches and is located on Hwy 21 off to the right just before crossing the Black River.  Expect to hear Lynyrd Skynyrd or other southern music playing at Lenny’s.  Soon after this location, be looking for signs for Taum Sauk State Park, which is off to the left.  The Taum Sauk Power Plant is accessible from Hwy U near Lesterville, if it ever re-opens to the general public.

From this location, head north on Hwy 21 to the town of Ironton, MO.  Another interesting lunch or dinner stop is the Mimosa Drive-in.  This small restaurant, located on Hwy 21 on the right, is an authentic 1950’s drive-in that serves excellent burgers, fries, and shakes.  McDonalds is also available for the less adventuresome but doesn’t offer near the character and charm of the Mimosa Drive-in.  The Kozy Korner Café on Main St. in Ironton is also a good place to find excellent homestyle food.  The Fort Davidson Café is also said to serve good food.  From Ironton, one can head north on Hwy 21 to Elephant Rocks State Park and Devil’s Honeycomb.  Hwy N and 21 form one large loop.

Hwy 72 branches off to the east from Ironton and heads towards the Silver Mines Recreation Area.  This turn-off is located off to the left before Mimosa or the Kozy Korner Café. This road is confusing since it heads west and then loops around to head east.  Follow Hwy 72 for a few miles until Hwy D is reached.  Follow Hwy D until it turns to gravel and then back to pavement.  Start looking for Silver Mines on the left soon after Hwy D turns back into paved road.  To get to Millstream Gardens, do not turn on Hwy D, and continue to follow Hwy 72 to the conservation area sign.  If you cross the St. Francois River, you have gone too far.  To get back to Rolla, backtrack from Silver Mines to Hwy 21.  Follow Hwy 21 north to Hwy 8 at Potosi and head home.  One can also follow Hwy 72 west, which will take them on a scenic but long route back into Rolla.

While in the towns of Arcadia, Ironton, Pilot Knob, and Graniteville, the architecture should be noted.  Many of the structures in these towns are made of local granite. Note the Victorian and gothic architecture common in Arcadia and Ironton.  The courthouse in downtown Ironton was built in 1857 and experienced the Civil War.  A mark left by a cannon ball is still present on the structure.  Much of the Civil War was fought in or near Iron County so Ft. Davidson and other Civil War sites are located nearby.  Spring St. in Arcadia is known for its spring complete with watercress.  The Iron County Museum is located in the town square of Ironton and offers visitors a description of the area’s rich history.

The locations featured here are only a small sampling of what the St. Francois Mountains have to offer. For a much more extensive description of the area, take a look at “Geologic Wonders And Curiosities of Missouri” and “Guidebook to the Geology and Ore Deposits of the St. Francois Mountains, Missouri.”  Although there are places to eat along the way, most of these parks have areas where a picnic lunch and/or dinner could be enjoyed.

(C) 2006 by Conor Watkins