3. This is a satellite
photo of the San
Pedro River Valley.
The San Pedro River
is a north-flowing
river which
originates in
Sonora, Mexico, runs
140 miles north and
meets up with the
Gila River in
Winkelman, AZ.
Photo Courtesy of:
Google Maps
4. The San Pedro River Valley is a rift valley that is part of the Basin-Range Faulting process which
began about 15 million years ago resulting in the extensional southeast to northwest block faulting of
the earth’s crust.. The above photos, adapted from the 2006 USGC Report FS 2006-3034 by Thomas
Blakemore, “Hydrogeologic investigation of the Middle San Pedro Watershed, Southeastern
Arizona”, depicts the San Pedro River Valley as the result of a long series of pull-apart rifting. The
rifting may have began occurring as long as 50 million years ago. This illustration could indicate the
formation of the valley over time.
Photos courtesy of www.sanpedrorivervalley.org
5. The first known people to inhabit the San Pedro
River Valley were the Clovis People more than
10,000 years ago. The Clovis People hunted
Mammoth in the Valley.
The next known inhabitants of the Valley were the
Cochise Indians followed by the Apache
Indians, and various European explorers.
Early American exploration of the Valley was in
search of beavers for their skins.
Mammoth photo courtesy of www.wizzyschool.com
Apache Indian photo courtesy of www.firstpeople.us/american-indian/people/at-the-ford-
apache.html
6. Modern day, the San Pedro River Valley
is home to hundreds of species of
animals including
birds, rodents, mammals, insects, and
reptiles.
The valley is also home to numerous
varieties of cacti. The top left photo
depicts a Curved-Bill Thrasher perched
atop a La Cholla Cactus. La Cholla
cactus are native to the San Pedro River
Valley.
The bottom left picture depicts a native
roadrunner. A common species in the
San Pedro Valley.
Photo of the roadrunner is courtesy of
www.tourcochisecounty.wordpress.com
Photo of the Curved-bill Thrasher is courtesy of Lon&Queta at
Flicker.com
7. This picture depicts animal life in the San Pedro Valley prior to the Megafauna
Extinction. Modern day species have changed in size and appearance since this
period of time. It has been determined that the Dodo bird roamed the San Pedro
Valley prior to the Megafauna Extinction.
Photo courtesy of www.sanpedrorivervalley.org
8. Another photo of ancient and extinct mammals of the San Pedro River Valley.
Photo courtesy of the Bureau of Geology and Mineral Technology.
9. The Dragoon Mountains are located in the heart of the San Pedro River Valley.
They are comprised of a mix of granitic rock and metamorphic sedimentary
rock that seem to chaotically shoot up from the ground. The mountain range is
about 25 miles long and is home to the Cochise Stronghold Memorial Park.
Cochise was one of the Apache Indian leaders who led the resistance of the
Americans in the 19th Century. The mountains were named after the 3rd U.S.
Cavalry, known as the Dragoons.
Photo courtesy of www.sanpedrorivervalley.org
10.
11. The top left photo is a more close up look
at the rock formations in the Dragoon
Mountains.
The bottom left photo depicts the typical
rock found in the Dragoon Mountain
formation. The rock is an igneous rock
that contains large amounts of fledspar
and quartz.
The two layers inside the rock are layers of
granite.
Top left photo courtesy of R. Weller/Cochise College
12. The top left photo shows fossilized fresh
water mollusks embedded in the
hardened clay on the walls of the river
bed. As the walls erode, the mollusks
begin to surface.
The bottom left picture shows fresh
water mollusks closer to the bed of the
river and under the surface of the water.
The mollusks are a fairly common
sighting in certain areas of the San
Pedro River Valley.
Photos courtesy of www.sanpedrorivervalley.org
13. The top left photo shows a desert rose.
The desert rose is made up of gypsum
crystals, barite, and sand. The “desert
rose” acquired that name because it is
located in the desert and are found to
frequently have the shape of a rose.
They are frequently found in the San
Pedro River Valley.
These stones typically have a very light
red tint, but are often white in color as
well. They are a sedimentary rock and
fall under the chemical subclass.
The chemical sub-class is a result of
repeated flooding and evaporation.
When the water evaporates, it leaves a
layer of dissolved mineral behind.
14. The top photo is a picture of Limestone.
Limestone is sedimentary rock that is
composed of mineral calcite and aragonite.
Limestone is frequently composed from
skeletal fragments of marine organisms
(see bottom photo)
and is a common sighting in the San
Pedro River Valley.
During the Devonian Period, Southern
Arizona was submerged in a warm
shallow ocean which was the result of the
limestone formations.
The bottom photo is a picture of limestone
with brachiopods. This rock is a Paleozoic
formation.
Photos courtesy of R. Weller/Cochise College
15. During the Jurassic Period of the
Mesozoic Era, tectonic movement and
igneous activity increased
exponentially. Volcanic activity also
increased. As a result, thick
sedimentary rocks are ground off the
fault blocks below the surface and
eventually move upwards.
During the Cretaceous Period, the San
Pedro Valley was once again flooded.
During the flooding, more sedimentary
rocks were swept in. As the waters
dissipated, the rock formations of the
Dragoon Mountains were revealed.
Photos courtesy of R. Weller/Cochise College
16. The top photo is a picture of mural
limestone in the San Pedro River Valley.
During the flooding of the Cretaceous
Period, this fossil-rich layer of limestone
was laid down. The limestone lies in an
unconformity with a total thickness of
4,000 to 5,000 feet in the upper formations.
There are large amounts of fist sized fossil
snails and clams exposed on these cliff
surfaces.
The bottom photo is a close up picture of
the mural limestone formations.
Photos courtesy of R. Weller/Cochise College
17. References:
Wikipedia contributors. "San Pedro River (Arizona)." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 29
Sep. 2011. Web. 17 Nov. 2011
Wikipedia contributors. "Cochise." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 27 Nov. 2011. Web. 2
Dec. 2011.
Wikipedia contributors. "Dragoon Mountains." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 27 Oct. 2011.
Web. 2 Dec. 2011.
Weller, Roger. "San Pedro Valley - Geologic History." Web. 03 Dec. 2011. <http://skywalker.cochise.edu/wellerr/geology-
SEAZ/san-pedro/San-Pedro-history.htm>.
Wikipedia contributors. "Desert rose (crystal)." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 6 Jul. 2011.
Web. 3 Dec. 2011.
Wikipedia contributors. "Limestone." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 2 Dec. 2011. Web. 3
Dec. 2011.
"Tombstone: Weather from Answers.com." Answers.com: Wiki Q&A Combined with Free Online Dictionary, Thesaurus, and
Encyclopedias. Web. 03 Dec. 2011. <http://www.answers.com/topic/tombstone-arizona>.
