Notes from the field: Mammoth Spring Quadrangle

DSCN2991Geologist Bill Prior inspects a small tufa dam near Riverside Resort on the Spring River, Fulton County, AR.

Geologic mapping of the Mammoth Spring 7.5 minute quadrangle was recently completed by the Arkansas Geological Survey’s STATEMAP field team. This project was funded in part by a grant from the National Cooperative Geologic Mapping Program through the United States Geological Survey. This is the 26th year of STATEMAP projects in Arkansas and represents an unprecedented effort in gathering geologic data within the state. STATEMAP was established in 1992 by a congressional act to encourage 1:24,000 scale mapping of geology by state geological surveys. Arkansas first participated in the STATEMAP program in 1994, and since then, the Survey has overseen the completion of eighty one, 1:24,000 scale geologic maps, including the Mammoth Spring quadrangle.

This year’s grant enabled the AGS to hire a geologist and partially cover field work expenses. Garrett Hatzell and staff geologists, Scott Ausbrooks and Bill Prior, worked together during the field data collection and map production phases of the project. This team approach has worked well for AGS mapping projects in the past, both for safety and efficiency.

The goal of STATEMAP is to classify and map rocks exposed at the surface into recognizable units, such as formations and members. Commonly, bedrock crops out along the sides or in the bottoms of creeks and rivers. For this reason, data collection in the major drainages is a priority. In areas where bedrock is covered, information may be inferred from data gathered at nearby outcrops. Since geologic formations are laterally extensive, disparate points taken on similar contacts can be connected across the mapping area to delineate each formation. Structural features, such as faults and folds, are also described and mapped.

Fieldwork for the mapping of Mammoth Spring quadrangle commenced on July 29, 2019 and continued until March 11, 2020 for a total of about 60 days spent in the field. From March through June, the geologists analyzed field data and prepared aspects of the geologic map. Formation contact lines and structural features were hand drawn on a topographic map base and were then digitally transcribed in ArcMap by Brian Kehner. The final layout of the map was completed in Adobe Illustrator by Garrett Hatzell, Angela Chandler, and Jerry Clark. Edits were provided by AGS staff geologists.

Printed copies of the Mammoth Spring geologic map (and many others) are available at the AGS office in Little Rock for $12.50, and digital copies may be downloaded free of charge as .pdfs from our website.

Here is the link to the recently completed Mammoth Spring quadrangle map: maps/24k/MammothSpring.pdf


Following a fatal accident at Saddler Falls on the Spring River in June of 2018, geologists from the Arkansas Geological Survey were called on to investigate a reported sinkhole that had caused the tragedy. Upon investigating the site, geologists observed that the falls present at this location were a series of tufa dams that spanned the river. Tufa, a type of limestone, is formed by the precipitation of calcium carbonate out of ambient temperature alkaline water. At Saddler Falls, a section of one of these dams had undergone a blowout of sorts at its base. Water began draining through this new opening at the base of the dam rather than flowing over the top as usual. This formed a dangerous whirlpool just upriver from the tufa dam structure. This new pathway was confirmed by performing a fluorescein dye trace at the whirlpool on June 25, 2018. After being poured into the whirlpool, the dye emerged about 15 feet away, just downstream of the tufa dam.

whirlpoolWhirlpool at Saddler Falls where a fatal accident occurred on June 9, 2018. Image courtesy of Arkansas Game and Fish Commission.

dye_traceDrone image of fluorescein dye trace (green) at whirlpool in Spring River near Saddler Falls on June 25, 2018. Dye emerged just below tufa dam after entering whirlpool. Image courtesy of BrainStorm Media.

The whirlpool hazard was mitigated on July 12, 2018 by using an excavator to remove the upper portion of the tufa dam, above the conduit, allowing water to flow freely through the dam. Subsequently, this area has become one of the most easily navigable areas of the many tufa dams along the Spring River.

tufadozerDestruction of tufa dam/whirlpool at Saddler Falls on July 12, 2018 by an excavator operated by Arkansas Game and Fish Commission. Image courtesy of Arkansas Game and Fish Commission.

remediated_whirlpoolArea after whirlpool was destroyed. Image courtesy of Arkansas Game and Fish Commission.

dry_tufa_damExposed tufa dam at Saddler Falls where whirlpool had formed.

tufa_dam_bottomThe underside of a tufa dam exposed by the excavator during mitigation of the Saddler Falls whirlpool.

The Spring River is a popular recreational river, attracting tens of thousands of tourists annually. After participating in the whirlpool mitigation effort and further observations of the tufa dams by AGS staff, it was determined that the Mammoth Spring quadrangle was of high importance for geologic mapping.

Tufa dams form on spring fed river systems around the world but had not yet received any thorough investigation in the Ozarks. Other large spring fed drainages in the area, such as Big Spring and the Current River in Missouri, do not produce tufa dams. Over 30 of these structures were documented and mapped on the Mammoth Spring quadrangle, and they continue to form downriver, off the quad, for many more miles. Small areas of tufa precipitation were also found on tributaries of the Spring River throughout the mapping area. Geologists from Missouri State University have also begun conducting studies of these tufa structures, which includes the coring of some of the tufa dams. The continued cooperation between the AGS and Missouri State University on this endeavor will hopefully lead to a better understanding of the formation and degradation of the tufa structures along the Spring River.

tufa_thin_sectionThin section of tufa dam material. Crumbly, porous calcite has loosely cemented chert and other alluvial gravels together, along with organic debris, to form the tufa dams. Image taken at 50x magnification with gypsum plate inserted for contrast.

MOstate_tufa_coringGeologists from Missouri State University coring a tufa dam near Riverfront Resort on the Spring River.

tufa_coating_ssTufa growth coating a sandstone cobble found in English Creek.

The Mammoth Spring quadrangle abuts the northern border of Arkansas, and lies within the Salem Plateau. The Salem Plateau is the oldest and most interiorly located of three broad plateaus that flank the Ozark Dome, centered in southeast Missouri, and together make up the Ozark Plateaus. Some 450 feet of Ordovician age carbonate and clastic rocks are exposed in the mapping area. These rocks formed from sediment deposited/precipitated in shallow epeiric seas which covered the area during that time. Only two formations were found to crop out within the mapping area: the Jefferson City Formation and the Cotter Formation.

Spring_River_raftingSTATEMAP team rafting down the Spring River.  

English_creekSTATEMAP team hiking/wading English Creek.

The Mammoth Spring quadrangle is drained by the Spring River and its tributaries. The largest and most extensive of these tributaries are Myatt and English Creeks. Geologic data was gathered along roughly fourteen miles of the Spring River which was traversed by the STATEMAP team via an inflatable raft. Both Myatt and English Creeks were hiked and waded along with numerous other smaller tributaries of the Spring River. Dolostone of the Cotter Formation is extensively exposed along the Spring River and its tributaries, across the vast majority of the quadrangle.

The Cotter consists of mostly gray-tan dolostone with interbedded chert nodules and small, sometimes oolitic, brecciated or conglomeratic chert layers, and sandstone lenses. Discontinuous sandstone lenses are increasingly abundant higher in the stratigraphic section. Mammoth Spring, in the northeast corner of the quadrangle, flows to the surface at almost 10 million gallons per hour. This flow travels for about 400 yards before joining the Warm Fork of the Spring River and continues southward. Near Mammoth Spring, the older Jefferson City Formation crops out as a 6-8 feet thick bench of conglomeratic/brecciated chert known as the Rockaway Conglomerate. Faulting to the south of Mammoth Spring, and a gentle southwesterly regional dip, take the Jefferson City into the subsurface as one travels south across the area.

Rockaway_boulderGeologist Bill Prior measuring a large boulder of the Rockaway Conglomerate near Old Town Spring in Mammoth Spring, AR.

Rockaway_outcropGeologist Scott Ausbrooks measuring the strike and dip of a steeply dipping exposure of the Rockaway Conglomerate, located 350 feet west of the Mammoth Spring.

If you have ever floated the Spring River, you would have almost undoubtedly noticed the busy BNSF railway line that runs along its east side. You likely would have also noticed the scenic natural rock exposures and the cuts created for the installation of this railway. The STATEMAP team was allowed the courtesy of a ride on the BNSF railroad in a hi-rail pickup truck to observe and record geologic data along the tracks. This led to the discovery and mapping of several exposed faults that otherwise would not have been recognized because weathering has covered them elsewhere.

rrnotesGeologists Scott Ausbrooks and Bill Prior taking notes while observing rock exposures along the BNSF railway which parallels the course of the Spring River through the mapping area.

rrcropOutcrop of Cotter Formation exposed along BNSF railway, adjacent to Spring River.

RRfaultFaulting in a Cotter Formation exposure along the BNSF Railway.

In addition to mapping, water samples taken from Mammoth Spring, the Spring River, the Warm Fork, and other nearby springs, were analyzed for a geochemical study of the area’s aquifers and surface waters. Characteristics such as conductivity and pH were measured in the field, while other chemical analyses were performed by the Laboratory Division of the Department of Energy and Environment in North Little Rock.

water_samplingWater sampling at Mammoth Spring, performed by STATEMAP team.

fracturedCotterHighly fractured dolostone bedrock of the Cotter Formation exposed in English Creek.

Special thanks to Dr. Doug Gouzie and his graduate students from Missouri State University for their involvement in the ongoing study of the tufa dams. Also a special thanks to Angela Chandler for writing the proposal and serving as this project’s Principal Investigator. A very special thanks to BNSF Railway for allowing us to ride along with them and examine all the outcrops we wanted to see. A special thanks to the staff of the Laboratory Division of the Arkansas Department of Energy and Environment for performing the chemical analyses on our water samples. Thanks also to all the private landowners who graciously allowed us access to their property.

Next year, STATEMAP will continue mapping adjacent to this area. The Stuart quadrangle, south of the Mammoth Spring quadrangle, will be the site of the next geologic mapping effort.

Notes from the Field: Weathers and Delaney Quadrangles


Parthenon in Felkins Creek

Parthenon Sandstone overlying Brentwood Limestone on Felkins Creek, Weathers quadrangle

Recently, geologists at the Arkansas Geological Survey (AGS) completed geologic mapping of the Weathers and Delaney quadrangles in northwest Arkansas. These quadrangles are part of the U. S. Geological Survey’s 7.5-minute topographic series and cover an area of approximately 120 square miles. This project was made possible by a grant from the National Cooperative Geologic Mapping Program of which STATEMAP is a part. This year marks the 25th year of STATEMAP projects in Arkansas and represents an unprecedented commitment to gathering data on the geologic features of our State. STATEMAP was established in 1992 by an act of Congress to encourage the states to map their geology at the 1:24,000 scale. The first grant received by the Arkansas Geological Survey, then known as the Arkansas Geological Commission, was for a proposal in fiscal year 1994.  Since that time, eighty, 1:24,000-scale geologic maps have been completed, including the Weathers and Delaney quads.

Printed copies of the new geologic maps (and many others) are available at the AGS office in Little Rock for $12.50, but they are also available as a free download in .pdf form on our website. Here’s the link to the Delaney Quadrangle:

Geologic Map of Delaney Quadrangle

And here’s the link to the Weathers Quadrangle:

Geologic Map of Weathers Quadrangle

STATEMAP, which is administered by the U. S. Geological Survey, provides Arkansas with federal dollars through an annual grant proposal process. These funds are matched by the AGS which then performs all the work necessary to produce new geologic maps for the State. This year’s grant enabled the AGS to hire a geologist and to partially cover expenses incurred during field work. Garry Hatzell and staff geologist Richard Hutto worked together as a team during the data collection and map production phases of the project. This team approach has worked well for the AGS during its long history of geologic mapping, both for safety and efficiency.

The goal of STATEMAP is to classify bedrock exposed at the surface into recognizable units, such as formations and members, based on a common lithology—basically, an areal inventory of surface materials. Unfortunately, bedrock outcrops are few and far between in our State because so much of the surface is covered by alluvium (stream deposits) or colluvium (slope deposits). Since we are mapping the bedrock geology, we have to find ways to see through this cover and infer what is beneath it. We do map certain types of surficial deposits in some areas, however. Along the valleys of mature streams for instance, alluvium and terrace deposits are mapped. On steep hillsides, various types of debris flows considered to have moved in the recent past are mapped as landslides. Structural features, such as faults or folds, that offset or deform rock units are also described and mapped. In areas where the bedrock is covered, these relationships are inferred from data gathered nearby where outcrops are better.

Landslide in Atoka near Frog BayouParthenon Boulders in Kings River

Recent landslide in the Atoka Formation on the Delaney quad (left) and boulders of Parthenon sandstone in Kings River on the Weathers quad (right)

For this reason, much of our data collection efforts are concentrated on stream beds. There, erosional processes have typically removed soil and loose rock leaving sporadic, well-exposed outcrops of bedrock to study. Also, following a streambed allows us to see strata from bottom to top (or vice versa) which puts each formation in context with others. Locating and describing the physical contacts between formations is one of the most important things we do while mapping. Because formations are laterally extensive, disparate points taken on similar contacts can be connected across the mapping area to delineate each formation. Drawing these contact lines between formations in the correct location is a major focus of the mapping process.

Parthenon/Brentwood at Kings River FallsParthenon/Brentwood in Crosses Creek

Contact between the Parthenon and Brentwood Members of the Bloyd Formation on the Weathers quad at Kings River Falls (left) and on the Delaney quad in Crosses Creek (right)

Currently, the AGS’s STATEMAP projects are focused on the Ozark Plateaus Province, part of the Interior Highlands Physiographic Region located in the northern part of the State. The Ozark Plateaus in Arkansas consist of three broad surfaces that have developed due to differential erosion of Paleozoic sedimentary rocks on the southern flank of the Ozark Dome. Weathers and Delaney lie within the Boston Mountains Plateau, the southernmost and highest of these three surfaces. On these quads, over 1000 feet (305 meters) of Mississippian to Pennsylvanian (Chesterian, Morrowan, and Atokan) carbonate and clastic rocks are exposed. These rocks formed from sediment deposited in distal to near shore marine, tidal, deltaic, and fluvial environments.

Boston Mountains Plateau from Boston, Ark.

On the Boston Mountains Plateau, looking west toward Delaney from Boston.

In this area, the White River is increasingly being utilized as a public water source. Because of its importance in this regard, there is a lot of interest in gathering baseline data in this watershed. Most of the Delaney quad is drained by the White River, the uppermost reaches of the Middle Fork of the White River, and numerous smaller tributaries of the White. Some small drainages along the west side of the quad and Frog Bayou along the southern edge drain to the Arkansas River. Most of Weathers quad is drained by the Kings River and its tributaries as well as upper reaches of War Eagle Creek and the Buffalo River, all of which contribute to the White. Field work this year included hiking, wading, and swimming about 4.5 miles of the White River and 7 miles of the Middle Fork of the White River on the Delaney quad. 11 miles of the Kings River and 10.5 miles of Felkins Creek were traversed on the Weathers, along with numerous other streambeds on both quads.

Fossiliferous Brentwood in White RiverFossiliferous Brentwood in Cowcumber Creek

Close examination of fossiliferous Brentwood Limestone in White River on Delaney quad (left). Crinoid detritus including spines and cup plates in the Brentwood in Cowcumber Creek on Weathers quad (right)

The most significant structural feature on Weathers is the Russell Ridge Monocline, the axis of which is oriented parallel to other northeast-trending faults and lineations in northwest Arkansas. Presumably these align with regional faulting of Precambrian basement rock. The strata are depressed approximately 200 feet (61 meters) from southeast to northwest across this structure. Various normal faults with throws from 60-100 feet (18-20 meters) were also mapped. In the northwest corner of Delaney, the Drakes Creek Fault, a normal fault that also trends northeast, is downthrown to the southeast approximately 200 feet (61 meters).

Normal fault in Whispering Hollow

Yellow line marking the trace of a normal fault in Whispering Hollow on Weathers. Pitkin (Mp) downthrown to Fayetteville (Mf) approximately 60 feet (18 meters)

The Ozark National Forest occupies parts of the southern two thirds of Delaney and the southern third of Weathers. It is managed by the U. S. Forest Service. Along a reach of the Kings River in the southern part of Weathers is the Kings River Falls Natural Area which is maintained by the Arkansas Natural Heritage Commission.

Kings River Falls

Kings River Falls, the centerpiece of the 1059-acre Kings River Falls Natural Area

Field work commenced on July 16, 2018 and was finished on March 28, 2019 for a total of 75 days. From early April through the end of June, the geologists analyzed field data, classified rock specimens, and wrote descriptions specific to each quadrangle. Contacts and structural features were drawn on a topographic map base both digitally and by hand. Brian Kehner and Kerstein Dunn helped digitize and symbolize the map elements in ArcMap, developed alternative base maps, and integrated field data into our seamless geodatabase. Final layout of the maps was accomplished in Adobe Illustrator by Garry Hatzell, and they were edited by AGS geologic staff.

Prairie Grove in Kings RiverAtoka in Shrader Hollow

Massive calcareous sandstone in the Prairie Grove Member of the Hale Formation in Kings River on Weathers (left). Thin-bedded sandstone in the Atoka Formation in Shrader Branch on Delaney (right)

Special thanks to Ciara Mills for accompanying us in the field several weeks this year. Also to Angela Chandler for writing the proposal and serving as Principal Investigator again this year. Her guidance and support of geologic mapping in the State inspires us all to do great things. Very special thanks to Jerry and Joan Johnson of Madison County whose hospitality and knowledge of the people and places in the mapping area provided invaluable support for our endeavor this year.

Joan, Richard, and JerryAngela

Joan Johnson, Richard Hutto, and Jerry Johnson by Little Mulberry Creek (left) and Angela Chandler on North Sylamore Creek (right)

Next year, STATEMAP is heading farther north to the Salem Plateau where Scott Ausbrooks, Bill Prior, and Garry Hatzell will be mapping the Mammoth Springs quadrangle. So if you see someone up there taking an unusually keen interest in the rocks, be sure to say hello.

Until next time, I’ll see you in the field!

Richard Hutto

 Team Ozark

Garry Hatzell and Richard Hutto—out standing in the field