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GEOLOGIC EVOLUTION OF THE GRAND CANYON
MITCHELL JENNINGS
ABSTRACT
The Grand Canyon is truly a natural wonder. Although many theories exist about how the
canyon formed, an exact timeline and series of events that explain how it was formed are still
unknown. This paper will cover stratigraphy of the canyon and geomorphology but will be
focusing on the uplift of the Colorado Plateau and the incision of the Colorado River into the
Grand Canyon. The pace and timing of plateau uplift is often debated and still unknown, but the
arrival of the modern Colorado River is marked by a large and localized extinction event that
occurred in a southern basin, what is now modern-day Lake Mead.
The most popular and widely accepted theories of the evolution of the Grand Canyon are
the Headward Erosion Theory and the Spillover Theory. The Headward Erosion Theory is the older
of the two and involves multiple drainage areas, a north flowing ancestral Colorado River, and a
pre-incised canyon that eroded headward and captured the Ancestral Colorado River to form the
Grand Canyon. The Spillover Theory suggests that a large basin was created to the north, filled
up due to a change in flow direction and spilt over the Colorado Plateau to form the Colorado
River which incised into the Grand Canyon.
Key Words: Grand Canyon, Colorado River, Laramide orogeny, geologic uplift
INTRODUCTION
The Grand Canyon is located in Northern Arizona and is situated between two large
manmade reservoirs, Lake Powell to the north and Lake Mead to the south. The dimensions of
the canyon are; 360 km long, 30 km wide (at the South Rim), and 1,830 m deep. The Grand
Canyon rock sequence has preserved at least eight sea transgressional events over a time span
of 1,500 Ma to 200 Ma. The driving force behind the formation of the Grand Canyon is the
Colorado River, but the canyon could not have reached its depth without plateau uplift. This uplift
was caused by a mountain building event known as the Laramide orogeny. This orogeny was
caused by the subduction of the Farallon plate under the North American plate, which occurred
around 70 to 80 Ma. The shallow subduction angle of the plate played a role in the unique uplift
of the area, now known as the Colorado Plateau.
Orogenic events usually result in the tilting of rock formations. The Colorado Plateau
exhibits significant uplift but minimal tilting, approximately 1.5 degrees, and the mechanics of
which are stilllargelydebated and unknown. Dr. Karl Karlstrom suggests thatduring the Miocene,
highlands created by the Laramide orogeny collapsed to form a basin and range. This inversion

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of topography left the Colorado Plateau higher and reversed flow directions within multiple
watersheds/drainages in the area. These new flow directions created new topographic valleys
and drainage channels that are responsible for the flow path of the modern Colorado River. “But
the Colorado River did not become integrated across the Kaibab Plateau and through western
Grand Canyon until after deposition of the Hualapai Limestone (ending 5.97 ± 0.07 Ma; Spencer
et al., 2001).” (Karlstrom et al., 2008)
BACKGROUND
The Grand Canyon is located in the arid Southwest United States and is world-renowned
for its horizontal bedding which preserves its geologichistory. The formation of the canyon began
around 2.0 Ga. The Vishnu Schist is the oldest in the Grand Canyon sequence and is a
metamorphosed igneous rock that was deposited as a result of the North American plate moving
over a hot-spot. This sediment was later metamorphosed by the Yavapai-Mazatzal orogeny
around 1.7 Ga (Fig.1).
Fig. 1 Regional map of Proterozoic provinces of western Laurentia (Karlstrom et al., 2004).

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At approximately 1.4 Ga, a large magma body intruded into the basement rock which formed
dikes and massive granite bodies within the schist rock. This granite intrusion occurred in two
phases, labeled I-1 and I-2 in (Fig. 2).
Figure 2. StratigraphicColumnof GrandCanyon(TASA GraphicArts, Inc.,2000)
During the middle to late Precambrian, a transgressional event deposited sediment that
makes up the Grand Canyon Supergroup. Over the next several hundred million years, orogenic
events lifted, tilted, and metamorphosed these sediments. Between the late Precambrian and
early Paleozoic eras, erosional events removed large portions of the Grand Canyon Supergroup
and left a relatively flat landscape.Theseerosional events created a Great Angular Unconformity,
which is asequence of tilted strata that contacts horizontal strata within a vertical sequence. (Fig.
2) This change in bedding dip tells geologists that information/stratigraphic history has been
erased. Continuing through the Paleozoic and Mesozoic eras, rising and falling sea levels
deposited around 4,600 meters of sediments that form the renowned flat sedimentary sequence
of the Grand Canyon.

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DETAILED STRATIGRAPHY
FORMATION NAME AVERAGE THICKNESS AGE DESCRIPTION
Chinle Formation 1,700 to 1,000 feet
thick
Late Triassic claystone, sandstone,
limestone, siltstone,
and conglomerate
Moenkopi Formation 2,000 feet Triassic Red,slope-forming,fine-
grained,thin-bedded
shaleysiltstoneand
sandstone.
Kaibab Formation 500-800 feet Upper Permian Reddish-grayand
brownish-gray,slope-
forminggypsum,
siltstone,sandstone,and
limestone
Toroweap Formation 300 feet Permian Includes,indescending
order,WoodsRanch,
Brady Canyon,and
SeligmanMembers
Coconino Sandstone 200 feet Lower Permian sandstone Tan to
white, cliff-forming,
fine-grained,
wellsorted, cross-
bedded quartz.
Hermit Shale 850 feet Lower Permian Red, slope-forming,
fine-grained, thin-
bedded siltstone and
sandstone. Contains
poorly preserved plant
fossils in channel fills in
lower part of
formation
Supai Group 550 feet Lower Permian,
Pennsylvanian,
and Upper
Mississippian
well-sorted
calcareous
sandstone (upper
unit), dark-red
siltstone, and gray
limestone (lower
unit)
Surprise Canyon
Formation
50 feet Upper
Mississippian
Dark-reddish-brown
siltstone and
sandstone, gray
limestone and
dolomite

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FORMATION NAME AVERAGE THICKNESS AGE DESCRIPTION
Redwall Limestone 650 feet Upper and Lower
Mississippian
Light-olive-gray,ledge-
and cliff-forming,thin-
bedded,fine-grained
limestone(upper),
Yellowish-grayand
brownish,fine-grained
dolomite (lower)
Temple Butte
Limestone
100 feet Upper and
Middle Devonian
Purple, reddish-purple,
and lightgray, fine- to
coarse-grained, thin- to
medium-bedded,
ripple-laminated
ledges of mudstone,
sandstone, dolomite,
and conglomerate
Tonto Group 1,500 feet Middle and
Lower Cambrian
limestone and
dolomite lithologies
belong to the Muav;
shale and siltstone
lithologies belong to
the Bright Angel; and
sandstone and
conglomerate
lithologies belong to
the Tapeats
Grand Canyon
Supergroup
2,200 feet Middle
Proterozoic
Includes,indescending
order,unnamed diabase
sillsanddikes,Cardenas
Basalt,Dox Formation,
ShinumoQuartzite,
Hakatai Shale,andBass
Formation
Zoroaster Granite Unknown Precambrian Granite plutons,stocks,
and pegmatite andaplite
dikesemplaced
synchronouslywithpeak
metamorphism
Vishnu Schist Unknown Precambrian Quartz-micaschist,
peliticschist,andmeta-
arenitesof
metamorphosed,arc-
basin,submarine
sedimentaryrocks

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HEADWARD EROSION THEORY
The Headward Erosion Theory suggests that the modern day Colorado River achieved its
present course by a combination of headward erosion and stream capture. In this model a pre-
incised canyon deeper than 600 m, formed on the western Hualapai Plateau by headward
erosion, continued along a strike-valley drainage, and captured ancestral Colorado River flow.
(Young, 2008) At this time, thought to be late Miocene, the ancestral Colorado River is projected
to flow southeast toward the Gulfof Mexico. Near modern day Little Colorado River,the ancestral
river turned northward toward the Gulf of California. This northward flow of the ancestral river
is key for the present Colorado River’s interception of ancestral river flow. (Fig.3)
Fig.3 Headward erosion of modern Colorado River (www.answeringenesis.org)
Headward erosion of this pre-incised canyon, modern Colorado River, captured ancestral
river flow and began directing the majority of water flow down the pre-incised canyon. After the
ancestral Colorado River was captured uplift of the plateau not only lifted the land around the
river but alsodirected the water flow of multiple watersheds and drainage areas into the modern
Colorado River. This massivevolume increaseof water flow combined with plateau uplift was key

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for the incision of the Colorado River into the Grand Canyon. (Fig. 4)
Fig. 4 Uplift around river channel
(http://www.dkimages.com/discover/previews/774/206778.JPG)

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SPILLOVER THEORY
Spillover Theory suggests that Kaibab uplift altered the flow of the Ancestral Colorado
River, forcing it to flow southeast toward the Gulf of Mexico. At some point around 12 Ma the
ancestral river’s path to the Gulf of Mexico was blocked. This blockage caused the river to back
up and create a large basin. (Fig. 5)
Fig. 5 Overflow diagram (www2.pvc.maricopia.edu)
This basin, thought to be Lake Bidahochi, continued to fill until it overflowed across the plateau.
The stream created by the overflow, followed topographic low areas across the plateau where it
combined with drainage flow and began to increase its volume and energy. Once the river
reached what is now southern Nevada, it started eroding massive amounts of sediment while
working its way down through the stratigraphic column and upstream towards the large
reservoir, it achieved this massiveheadward erosion via aseries of water falls.Thesehigh-energy
waterfall areas began to erode and incise into the landscape very rapidly to create the modern
path of the Colorado River and eventually the Grand Canyon. (Fig. 6)
Fig. 6 Diagram of Lake Bidahochi (www.kaibab.org)

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DISSCUSION
Although Heardward Erosion Theory and Spillover Theory are the most widely accepted,
they are not without their faults. Headward Erosion Theory requires a pre-incised canyon and a
north flowing Ancestral Colorado River. Problems with these two requirements lie within age
dating of the pre-incised canyon and evidence of a north flowing ancestral river. Lucchitta
suggests that the interception/stream capture point of the Ancestral Colorado River occurred
between the Shivwits Plateau and the Kaibab uplift where the ancestral Colorado River possibly
turned northward. (Lucchitta, 1989) Contrary to the idea of headward erosion leading to the
capture of a north flowing ancestral river, Spencer suggests that there is evidence to support
insufficient headward erosion. He claims that the distance of headward travel, 270 km, is too far
for accelerated down cutting to be transmitted upstream and across at leasttwo drainage divides
all as a result of a few hundred meters in subsidence. (Spencer, 2001)
Problems with the Spillover Theory begin with lackof evidence that supports abasin large
enough to create the Grand Canyon. Meek and Douglass denote Lake Bidahochi as being the
basin that overflowed across the plateau. Dickinson argues against Meek and Douglass
suggesting that Lake Bidahochi’s water level never reached an elevation high enough to spill over
the plateau. He stated that “Bidahochi paleogeography indicates that Hopi Lake was a playa
system that never achieved appreciable depth”. (Dickenson, 2013) Dickenson also suggests that
topographic profiles in northern Arizona are not compatible with the Spillover Theory and could
not have happened without post-basin deformation and/or pre-canyon-cutting that altered the
landscape in a way that in inconsistent with geologic evidence.
CONCLUSION
Findings suggest that Miocene topographic inversion left the Colorado Plateau higher,
reversed some drainages,and created significantfaultscarps atthe western edgeof the Colorado
Plateau. (Karlstrom et al., 2008) These drainages and faulted areas played a large role in
transporting water to the Colorado River but more information is needed to establish a timeline
as to when and how the Colorado River trough was formed. Unconformities within the canyon’s
stratigraphy combined with massive erosion of the landscape make determining the geologic
evolution of the Grand Canyon a near impossible task. Though it is largely debated on how the
Grand Canyon was formed, geologists are comfortable with the fact that the Colorado River was
the driving force behind the canyon’s incision. Weather the Grand Canyon was formed due to
the Headward Erosion Theory, Spillover Theory, or possibly even a combination of the two, at
this time definitive evidence has not been found.

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