The san pedro river valley in arizonaPresentation Transcript
Geology 3Field Assignment By: S. Weimer
This is a satellitephoto of the SanPedro River Valley.The San Pedro Riveris a north-flowingriver whichoriginates inSonora, Mexico, runs140 miles north andmeets up with theGila River inWinkelman, AZ.Photo Courtesy of:Google Maps
The San Pedro River Valley is a rift valley that is part of the Basin-Range Faulting process whichbegan about 15 million years ago resulting in the extensional southeast to northwest block faulting ofthe earth’s crust.. The above photos, adapted from the 2006 USGC Report FS 2006-3034 by ThomasBlakemore, “Hydrogeologic investigation of the Middle San Pedro Watershed, SoutheasternArizona”, depicts the San Pedro River Valley as the result of a long series of pull-apart rifting. Therifting may have began occurring as long as 50 million years ago. This illustration could indicate theformation of the valley over time.Photos courtesy of www.sanpedrorivervalley.org
The first known people to inhabit the San PedroRiver Valley were the Clovis People more than10,000 years ago. The Clovis People huntedMammoth in the Valley.The next known inhabitants of the Valley were theCochise Indians followed by the ApacheIndians, and various European explorers.Early American exploration of the Valley was insearch of beavers for their skins.Mammoth photo courtesy of www.wizzyschool.comApache Indian photo courtesy of www.firstpeople.us/american-indian/people/at-the-ford-apache.html
Modern day, the San Pedro River Valleyis home to hundreds of species ofanimals includingbirds, rodents, mammals, insects, andreptiles.The valley is also home to numerousvarieties of cacti. The top left photodepicts a Curved-Bill Thrasher perchedatop a La Cholla Cactus. La Chollacactus are native to the San Pedro RiverValley.The bottom left picture depicts a nativeroadrunner. A common species in theSan Pedro Valley.Photo of the roadrunner is courtesy ofwww.tourcochisecounty.wordpress.comPhoto of the Curved-bill Thrasher is courtesy of Lon&Queta atFlicker.com
This picture depicts animal life in the San Pedro Valley prior to the MegafaunaExtinction. Modern day species have changed in size and appearance since thisperiod of time. It has been determined that the Dodo bird roamed the San PedroValley prior to the Megafauna Extinction.Photo courtesy of www.sanpedrorivervalley.org
Another photo of ancient and extinct mammals of the San Pedro River Valley.Photo courtesy of the Bureau of Geology and Mineral Technology.
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 sedimentaryrock that seem to chaotically shoot up from the ground. The mountain range isabout 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 theAmericans in the 19th Century. The mountains were named after the 3rd U.S.Cavalry, known as the Dragoons.Photo courtesy of www.sanpedrorivervalley.org
The top left photo is a more close up lookat the rock formations in the DragoonMountains.The bottom left photo depicts the typicalrock found in the Dragoon Mountainformation. The rock is an igneous rockthat contains large amounts of fledsparand quartz.The two layers inside the rock are layers ofgranite.Top left photo courtesy of R. Weller/Cochise College
The top left photo shows fossilized freshwater mollusks embedded in thehardened clay on the walls of the riverbed. As the walls erode, the mollusksbegin to surface.The bottom left picture shows freshwater mollusks closer to the bed of theriver and under the surface of the water.The mollusks are a fairly commonsighting in certain areas of the SanPedro River Valley.Photos courtesy of www.sanpedrorivervalley.org
The top left photo shows a desert rose.The desert rose is made up of gypsumcrystals, barite, and sand. The “desertrose” acquired that name because it islocated in the desert and are found tofrequently have the shape of a rose.They are frequently found in the SanPedro River Valley.These stones typically have a very lightred tint, but are often white in color aswell. They are a sedimentary rock andfall under the chemical subclass.The chemical sub-class is a result ofrepeated flooding and evaporation.When the water evaporates, it leaves alayer of dissolved mineral behind.
The top photo is a picture of Limestone.Limestone is sedimentary rock that iscomposed of mineral calcite and aragonite.Limestone is frequently composed fromskeletal fragments of marine organisms(see bottom photo) and is a common sighting in the SanPedro River Valley.During the Devonian Period, SouthernArizona was submerged in a warmshallow ocean which was the result of thelimestone formations.The bottom photo is a picture of limestonewith brachiopods. This rock is a Paleozoicformation.Photos courtesy of R. Weller/Cochise College
During the Jurassic Period of theMesozoic Era, tectonic movement andigneous activity increasedexponentially. Volcanic activity alsoincreased. As a result, thicksedimentary rocks are ground off thefault blocks below the surface andeventually move upwards.During the Cretaceous Period, the SanPedro Valley was once again flooded.During the flooding, more sedimentaryrocks were swept in. As the watersdissipated, the rock formations of theDragoon Mountains were revealed.Photos courtesy of R. Weller/Cochise College
The top photo is a picture of murallimestone in the San Pedro River Valley.During the flooding of the CretaceousPeriod, this fossil-rich layer of limestonewas laid down. The limestone lies in anunconformity with a total thickness of4,000 to 5,000 feet in the upper formations.There are large amounts of fist sized fossilsnails and clams exposed on these cliffsurfaces.The bottom photo is a close up picture ofthe mural limestone formations.Photos courtesy of R. Weller/Cochise College
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>.