Geological Analysis by Morris Hall

Overviews are given for the following topics:


Physiography of Missouri

Climate of Missouri

Geology of Missouri

Regional Surface Geology

Regional Structural Geology

Local Surface Geology

Local Structural Geology

Surface Hydrology

Subsurface (Groundwater) Hydrology - Toronto Springs Watershed

Topography and Aerial Photos of T-Junction and Sinkhole Dig

Topography and Aerial Photos south of Montreal


Physiography of Missouri


Missouri can be divided into several distinct physiographic provinces:


(1)   Glaciated Plains to the north of the Missouri River

(2)   Western Plains extending into Kansas

(3)   The Southeastern Lowlands extending into northeastern Arkansas and Tennessee and

(4)   The Ozark Mountains which extend into northern Arkansas.



Reprinted from Missouri Dept. of Natural Resources (MDNR)

Physiography (cont.)


A Landsat 5 image from the south-central Missouri Area shows the Lake of the Ozarks area and the major drainage area of the Osage River Basin.

Eros Data Center



A Landsat 7 image shows the river drainages and upland areas of the Salem and Springfield Plateaus.

  Eros Data Center

Climate of Missouri


The south-central Missouri area near Carroll Cave receives an average of over 40” of precipitation per year.







The average air temperature in south-central Missouri around Carroll Cave is about 56 degree F.










Geology of Missouri


The geology of the state is quite interesting and complex.  The geologic periods of most direct interest in regards to the formation of caves in the center part of the state are the Ordovician period, the Pennsylvanian period, and the Quaternary period of geologic history.









The Ordovician Period is when a shallow, saline sea covered the southern part of the state, and limestone was deposited at the shelf and shelf margin of this sea.  The Pennsylvanian period is when the Ordovician shelf limestones were probably altered to form dolomite and tectonic forces caused faults, fractures and joints to develop in Ordovician aged dolomites.  The Quaternary period is when the Ozark dome formed.  Many of the caves we can enter today in the Ozarks had their origins in the Pliocene or Pleistocene epoch of the Quaternary period.


A brief history of the Ordovician and Pennsylvanian Periods is given below (Missouri World Geology by Jo Shaper):




Regional Surface Geology


 Most of the surface rocks exposed in the central portion of the state are Ordovician in age.


Part B

An enhanced Landsat 5 image around the Lake of the Ozarks shows a red to blue color change, which might mark the Roubidoux-Gasconade contact in this area.


Eros Data


Regional Structural Geology


The southern Missouri Ozarks has been influenced by several structural events, which affected the Carroll Cave area.  The following is a relief topographic map  enhanced to highlight the rivers and surface topography of Missouri and surrounding states.  The Ozark uplift is seen south of the Missouri River into northern Arkansas (dark green).  The Ouachita Uplift (light-green/ east -west trending folds and faults) at the very southern part of the display influenced




the Ozarks by deforming the Cambrian-Ordovician cave forming strata during Pennsylvanian time.


This structural event created a series of northwest-southeast trending folds and fractures in the Cambrian and Ordovician strata, which can be mapped today.

A secondary set of fractures associated with the primary set is often seen trending northeast – southwest.   The Ozark Uplift is a late Pliocene-Early Pleistocene event, which caused structural doming away from the center of uplift of southeastern Missouri.  This doming complicated the preexisting geologic structure by overprinting and reactivating the Pennsylvanian aged fold, fault, and fracture patterns of the Ouachita Uplift.



Two additional pre-Roubidoux structural highs exist away from the primary Ozark uplift:


(1)    An uplift in Morgan and Camden county which brings the Gasconade and Eminence Formations to the surface and

(2)    Pulaski County where the Gasconade is prevalent at the surface.











Local Surface Geology


The southeast portion of Camden County is primarily covered with Roubidoux Sandstones and dolomites at the surface.  The Decaterville Structure is seen as a

circular feature to the southwest of Carroll Cave.  Precambrian granites are




Oj- Ordovician- Cotter and Jefferson City Formation- fine-grained dolomite, with oolitic chert

Or- Ordovician- Roubidoux Formation- sandstone,  chert and fine-grained dolomite

Og-Ordovician- Gasconade Formation-coarsely crystalline, cherty dolomite with basal sandstone (Gunter) member

Cep-Cambrian-  Eminence Formation- coarsely crystalline, vuggular, cherty dolomite




exposed at the surface in the center of the Decaterville structure.  Carroll Cave is located northeast of this feature.


The Lower Gasconade outcrops at the entrance to Carroll Cave on the flanks of Mill Creek Valley.  The tops of many of the hills and ridges around Carroll are formed from the Roubidoux sandstone and dolomite formation.





Bedrock is exposed near or at the surface over much of the Montreal Quadrangle.




Local Structural Geology


The Decaterville Structure folded and faulted the Gasconade dolomite near Carroll Cave.  An up to the east fault exists several miles west of Carroll on the east side of the Decaterville structure.  Carroll Cave is developed on the east flank of this feature.  The Gasconade dips to the east on this monocline at less than ½ of 1 degree (about 45’ per mile) in the vicinity of the cave. The elevation on the Base of Roubidoux-Top of Gasconade formation contact is about  925’ AMSL around Montreal, Missouri.



 MDNR    Carroll Cave Area

Shows pre-Roubidoux outcrops in red.  Top of GasconadeFormation in orange contours.


Surface Hydrology


A topo map shows the relationship of drainage to topography in the Montreal area.

The Osage River is the master surface stream, which all other streams drain to in the area.



Part C

UMC  Toronto Springs


Surface drainage to the northeast of Carroll Cave is to Mill Creek and the Wet Glaize.  Toronto Springs, one of the discharge points for Thunder River, is located to the northeast of the cave.



A color topo map around the cave and Montreal area shows the drainage of the

surface streams to the north, northeast, and east.

Subsurface (Groundwater) Hydrology-Toronto Springs Watershed


The potential drainage area for the Toronto Springs watershed is about 22 square miles.  Given an average rainfall of 40 inches a year, this would mean that over 15 billion gallons of water fall on the watershed in a single year.  Given that Toronto Springs flows an annual of about 1.6 billion gallons per year, most of the rainfall on the watershed runs off as surface water, is transpired, evaporated, or flows out of the watershed as groundwater not associated with Toronto Springs.

Toronto Springs Watershed


A water-table contour map around the Montreal Quadrangle is based on water-table elevations from several sources:

(1)   Ozark Fisheries

Water Table Elevation = 779’ AMSL

(2)   Toronto Spring

Water Table Elevation =  710’ Above Mean Sea Level  (AMSL)



(3)   Carroll Cave –Carroll River

Water Table Elevation = 780 ‘ Above Mean Sea Level






(4)   T-Junction Stream Level



Water Table Elevation  = 795’ AMSL (estimate)




The Water Table of the Gasconade Aquifer is then interpreted to be:


Contour Int.=20’

                                                820’                 800’          780’


Note that groundwater is flowing both to the northeast below Barnett Hollow and to the east and southeast below Traw Hollow.


Part D

Topography and Aerial Photos of T-Junction and Sinkhole Dig










Old Dig Site



Old Dig                                                                                                   T Junction                                                                                                                                                                                          

Topography and Aerial Photos south of Montreal

 The plateau south of Montreal is littered with sinkholes and sinkhole ponds.



The potential for Carroll to extend to the west beneath Highway 7 is quite high based on the number and density of sinkholes and sinkhole ponds.