Rocks of Mohave County, Arizona

By Wilson, Doyle C Montbriand, Timothy

ABSTRACT The creation of an educational geologic display at the Lake Havasu City campus of Mohave Community College was accomplished by collecting boulder-sized specimens of representative rock types that occur within the boundaries of Mohave County, Arizona. The intent of the display is to offer students something more comprehensive than hand specimens, to inform residents and visitors of the county’s geologic diversity and history as well as to provide curriculum opportunities for K-14 in geology. Forty-nine boulders typifying rock types of the Basin and Range, the Colorado Plateau, and the Colorado River extensional corridor are labeled with a rock description and a map of the collection locality. An informative geologic timeline incorporated with the Colorado Plateau display and more in-depth information on the college’s science website provide students and citizens with a good introduction to various concepts in geology. These components, accompanied by biological, environmental, and meteorological campus displays and by similar information on the website, are part of a growing program to promote natural science within the county.

INTRODUCTION

College students in freshman geology classes and K-12 students in Earth science classes are typically exposed to hand specimens as they are learning about different mineral and rock types in laboratory settings. Although good hand specimens may invoke the essence of what is expected to be understood, there are rock textures and formation features such as large scale foliation, stratigraphie relationships, or cross-cutting features associated with certain rocks that are often lost in hand specimens, yet may be present in boulder-sized examples. The arid climate or Mohave County, Arizona, located in northwestern Arizona, bordering California, Nevada, and Utah (Figure 1), precludes extensive vegetation cover, exposing boulder-sized examples of many different rock types. Many people who visit the area do not know what kind of rocks they are seeing and since many students have communicated that they learned so much more about geology from looking at outcrops and boulders on field trips, a decision was made in 2003 to collect and place large specimens in a display on the Lake Havasu City campus of Mohave Community College (MCC). The landscape display is intended to educate K-14 students and the generalpublic about geological processes, and to showcase the geologic diversity of the county.

Geo-educational landscaping, similar to that developed on other college campuses, emphasizes general geologic concepts, which are most often taught through the integral processes of field experience and geologic mapping (Dillon et al., 2000; Caledrone et al., 2003; and Matty, 2006). The MCC display focuses on local geology while providing samples large enough to exemplify geologic features and concepts that hand specimens alone cannot provide. Added to the landscape design and to the overall educational experience are a geological timeline and a fence-like rail system consisting of geological structures and stratigraphie features.

REGIONAL GEOLOGIC PERSPECTIVE AND ROCK COLLECTION

Any educational institution wishing to promote the natural history of its region by establishing a geological display will utilize local specimens. Collecting a comprehensive display of local specimens presented a challenge since Mohave County, at almost 13,500 mi2, is the fifth largest county in the conterminous United States, larger than nine states (including Maryland by 3761 mi^sup 2^). All three major geologic provinces recognized in Arizona-the Colorado Plateau, the Basin and Range, and a transitional central highland zone-are present in Mohave County, although the transitional zone is relatively narrow. The Basin and Range province is informally subdivided to include the Colorado River extensional corridor, an approximately 50-mile-wide zone centered on the Colorado River and dominated by surface and near-surface low angle detachment faulting due to heating of the lower and middle crust during the Tertiary Period (Nielson and Beratan, 1990).

Boulder-sized specimens were collected utilizing an eight-foot- long, homemade trailer with a boom and a pulley/chain system to mechanically pick up and transport the boulders. Rocks from the Colorado Plateau consist of Proterozoic and Paleozoic formations that are found in the Grand Canyon and Virgin River Gorge, Mesozoic strata present in Zion National Park, and Quaternary volcanic rocks that overlie the older sedimentary rocks (Lucchitta, 1987; Wenrich et al., 1996; Billingsley et al., 2000; Billingsley and Workman, 2000; and Billingsley et al., 2001). Rocks collected from the Basin and Range and the Colorado River extensional corridor in Mohave County are quite varied, consisting of Proterozoic or Tertiary examples from all three major rock families, including some oddities such as highly cemented megabreccia (Miller and John, 1999, Howard et al., 1999) and volcanic rock altered to almost pure kaolin (Gray et al., 1990). The lone rock type accessible within the transition zone in the county is a Proterozoic fine-to-medium crystalline granite (Beard and Lucchitta, 1993).

Figure 1. Location of Mohave County in Arizona, approximate boundaries for the recognized geologic provinces in the state, and MCC Lake Havasu Campus Map with locations of boulder displays.

CAMPUS BOULDER AND GEOLOGIC TIME DISPLAYS

Forty-seven rock types are organized by geologic province on three separate locations of the campus (Figure 1). Since the transition central highlands province in Mohave County is very narrow, the single sample of that province was included with the sixteen specimens from the Basin and Range (Figure 2). Twelve rock types occurring in the Colorado River extensional corridor were placed at a separate location from the Basin and Range display. Eighteen formations from the Colorado Plateau in Mohave County were placed in chronological order along a 180-foot, straight stretch of sidewalk (Figure 3). This strategy highlights the sequence of deposition in the area and provides an opportunity for observers to experience the stratigraphy of both Grand Canyon and Zion national parks. Experiencing the sequence of deposition in this way is particularly educational for those individuals who may not be able to access either park.

Engraved signs indicating the geologic province of the rock are posted next to each boulder and contain the following information: a rock description that usually includes the rock’s age and something specific to the specimen for the visitor to examine, a county outline map with a star showing the approximate collecting location, and a list of sponsors of the project (Figure 4). Each of the three groups of rocks contains an introductory sign that briefly describes the nature of the geologic province. In the case of the Colorado Plateau, an introductory sign is placed at each end of the row of boulders so that visitors can start their "walk through time" from either end. A stratigraphie column illustration is also included to orient the visitor.

MCC received a National Science Foundation grant in 2005 to construct a geologic timeline consisting of a series of fifteen 18” x 24” anodized aluminum panels. The panels were attached to rebar stands welded by the college’s art students and erected behind the boulders of the Colorado Plateau display in concert with the appropriate time period of the boulders. Because of this chronological arrangement, the signs are not equally spaced as the number of boulders representing any particular time period varies. The purpose of the timeline is to convey the concept of dynamic change throughout Earth’s history while the visitor "walks through time." Information on the panels includes the name and time range of each geologic interval; the Hadean, Archean, ana Proterozoic eons, subdivisions of the Precambrian Eon (Condie and Sloan, 1998) and the 12 Periods of the Phanerozoic Eon. Written and graphical information about continental positions, including the approximate position of Arizona (except on the Archean and Hadean panels), global tectonics, local geology, and major life developments of each interval are explained (Figure 5). Since tne continental positions are not known for the Archean Eon and no real continents existed during the Hadean Eon, the panels respectively exhibit a world map with the known distribution of exposed Archean-aged rocks and the formation of both the solar system and the Earth-moon system.

The sign posts are connected by a fence-like rail system, made of three tiers of welded rebar, depicting sedimentary layers that contain structural and stratigraphie features (Figure 6) including a volcano, a magma intrusion, anticlines and synclines, a normal fault, a reverse fault with a drag fold, horsts and grabens representing the Basin and Range geologic province of the desert southwest, a paleo-stream channel, and an unconformity. The intent of the structural features is to impart the dynamic nature of Earth processes that can disrupt otherwise horizontal sedimentary layers. Preserved stratigraphic features in a sedimentary rock exemplify clues that can be used to interpret the geologic history of an area. A sign at the beginning of the geologic timeline display gives visitors a perspective to better understand and interpret the information on the signs and the features on the rail system. Figure 2. Example of boulder displays in the Basin and Range section.

Figure 3. Rocks of the Colorado Plateau and geologic timeline with rebar rail system. MCC art students constructed the "volcano" in the foreground.

Figure 4. Typical specimen sign depicting the rock’s geologic province, description, and collection locality, as well as the project’s sponsorship.

Figure 5. Devonian Period panel of the geologic timeline indicating the positions of the continents, global and local geology, and life development during the period.

STUDENT AND PUBLIC EDUCATION

Seven primary and secondary school field trip activities and six college level activities were developed to help teachers utilize the display for class field trips and are accessible for downloading from the Mohave Community College website www.mohave.edu/ pages/ 881.asp , which is the main page for the Rocks of Mohave County Project. These activities are also intended to give teacners an idea of what they can develop to best suit their students. Examples of K- 12 activities are the classification of rocks into one of three families (igneous, sedimentary, or metamorphic) by examining the rocks close-up and describing the rock texture, taking a visualization "walk through time" along the Colorado Plateau display, graphing the location of Arizona (and thus Laurentia/North America) through geologic time, determining what causes rocks to be a certain color, measuring faults and folds to determine crustal movement, and distinguishing different types of volcanic rocks and their origins. These activities utilize geologic information both from the boulders and their complementary signs, and from the geologic timeline components.

An assessment or the geologic display’s impact on K-12 learning shows mixed results. Local schools have visited the boulder display on formal field trips and local K-12 teachers sporadically conduct learning activities based on information they have received from the Rocks of Mohave County project. However, competing demands for inclusion in the K-12 science curriculum and the increasing constraints placed on the process of amending the curriculum has forestalled the incorporation of these learning activities into the regular curriculum. Notwithstanding, efforts to make the educational display a prescribed and measurable part of the K-12 science curriculum continues through consultation between the project directors and the area teachers.

Figure 6. Close-up of a section of the geologic timeline rail system showing a reverse fault with a drag fold.

Activities for introductory physical and historical geology college courses include developing a stratigraphic column and a stratigraphic section, and three activities covering aspects of identifying igneous, sedimentary, and metamorphic rocks. Most of the boulders collected highlight textural, compositional, stratigraphie, or structural features such as volcanic flow banding, xenoliths, foliation, mineral crystal interrelationships, chemical stain fronts, cross-bedding, ripple marks, fossil assemblages, and shearing that are useful in generating laboratory activities. The stratigraphie column and section activities lead students through the various rock displays and the geologic timeline to the discovery of why rock types and ages vary from one geological province to another. These two activities, which tie in with the North American tectonic activity, also explore the succession of depositional environments and unconformities presented in the Colorado Plateau display. Both broad geological concepts and an understanding of the region’s textbook geologic history are conveyed through the use of rocks collected directly from the area. Rock resistance to weathering is included in two of the activities, giving an indication why not all rock types form boulders or cliff faces.

The assessment of the educational impact of the boulder display and geologic timeline on introductory physical and historical geology college courses is ongoing. Students in those introductory courses have commented that they better appreciate the geologic concepts taught in the classroom once they have worked with the visual attributes of the display and its associated lab activities. Although not strictly scientific, the scores on homework assignments and quizzes given to students in four particular classes increased when the classes utilized the Rock of Mohave County display as opposed to scores on test topics covered in the same classes that did not involve referencing the display.

Various other links from the main webpage provide more in-depth information about the rocks in each of the three displays, including photos of the rock texture and outcrops of the area from which the boulders were collected. A link on the webpage, called "What Rocks Can Tell Us," gives a brief introduction about the types of information that can be extracted from rocks. This information source, comprised of various educational activities, can be useful in most any curriculum designed to give students the ability to interpret geologic processes. The boulders are used as examples to illustrate rock origin and history, and to identify the environmental conditions (including paleontological) in which they formed. An introduction to the geologic timeline project is also presented on the website to give potential visitors and teachers a perspective on what the timeline has to offer. Virtual geologic trips to locations within Mohave County and the surrounding area span the three geologic provinces of the region and give visitors a broader perspective concerning the origin and natural setting of many of the rock types in the campus display (www.mohave.edu/pages/ 587.asp).

A quantitative assessment of the ROCKS of Mohave County website can be estimated by the number of visits to the site. The website and its parent website (the Mohave Community College Science page) averaged over 300 hits and almost 3000 hits respectively, over three academic, nine month periods. A qualitative assessment of the website’s efficacy is more elusive as the type of visitor to the website (i.e. student vs. general public) is unknown. Moreover, most colleges or universities include some factor of local geology in their teaching, yet daily field trips to view the geology may not be feasible. The virtual field trips can be accessed outside of the classroom time block, leaving more time for explanation and discussion. The virtual field trips are also of great benefit to those students who are unable to withstand the physical demands of field activities. In addition, the website reaches a wider academic community and presents itself as a resource for geological information about the local region. Science departments at other community colleges have added this site to their geology links for their students to access.

In addition to its use by local school groups, college classes, and individuals who have visited the display for science or general education classes, the information presented throughout the display is also appropriate for rockhound clubs and individuals who want to know more about geology and the natural history of the region. The general benefits of the display are evident. More than 47 types of rocks or formations exist in Mohave County (funding and accessibility restricted the overall number of sampled specimens). The specimens collected represent a fair share of the county’s rock diversity, and the geologic timeline connotes a perspective of the ages given for each of the formations and the structural deformation that may befall existing rock. Although not in outcrop form, the MCC display brings the local geology to the campus in an easily accessible fashion not only for local schools and college classes to utilize, but also for the public to study and enjoy. The project has received great praise both from the local rockhound groups and from individuals, but any assessment, beyond a simply anecdotal one, of the impact of the educational display on the public is difficult to make. Individual visitors to the educational display experience it in different ways. Some experience the full stratigraphie sequence and note the effects of formation and deformation; others simply access the educational display to identify, from one of the display boulders, a rock in their backyard or a certain mineral source. It is perhaps the nature of public, general education displays that they are difficult to evaluate. The Rocks of Monave County educational display stands ready to impart information in any manner of ways.

ACKNOWLEDGMENTS

This project was funded by grants from Mohave Community College, the Mohave Community College Foundation, the Lake Havasu Gem and Mineral Club, and the National Science Foundation (Grant Award No. GEO-0507422).

The authors would like to express their many thanks to Al Montbriand and Carl Rovey who supplied the vehicle and trailer to haul the boulders, and to the three Bureau of Land Management districts covering Mohave County, the Arizona Department of Transportation, and the National Park Service for the permits to allow the collection of boulders. We would also like to thank the MCC Lake Havasu campus maintenance crew for their help and Gold Star Engraving for their help in producing the signs. A special thanks goes to George Billingsley and Keith Howard of the U. S. Geological Survey and to Ernest Duebendorfer of Northern Arizona University for their help in the search for formation accessibility and the identification of rock types. Lastly we would like to thank the students of the Lake Havasu campus who helped with the construction of the geologic timeline.

REFERENCES

Beard, L. S. and Lucchitta, L, 1993, Geologic map of the Valentine Southeast Quadrangle, Mohave County, Arizona, GQ-1711, 1 sheet. Billingsly, G. R., Harr, M. L., and Wellmeyer, J. L., 2000, Geologic map of the upper Parashant Canyon and vicinity, Mojave County, northwestern Arizona, MF-2343, 27 p. (1 sheet).

Billingsley, G. H. and Workman, J. B., 2000, Geologic map of the Littlefield 30′X60′ quadrangle, Mohave County, northwestern Arizona, 1-2628, 25 p. (1 sheet).

Billingsley, G. H., Hamblin, W. K., Wellmeyer, J. L., and Dudash, S. L., 2001, Geologic map of part of the Uinkaret volcanic field, Mohave County, northwestern Arizona, MF-2368, 34 p. (1 sheet).

Calderone, G. J., Thompson, J. R., Johnson, W. M., Kadel, S. D., Nelson, P. J., Hall-Wallace, M., and Butler, R. F., 2003, Geoscape: An instructional rock garden for inquiry-based cooperative learning exercises in introductory geology courses: Journal of Geoscience Education, v. 51, p. 171-176.

Condie, K. C. and Sloan, R. E., 1998, Origin and Evolution of Earth: Principles of Historical Geology., Prentice Hall, Upper Saddle River, NJ, 498 pages.

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Howard, K. A, Nielson, J. E., Wilshire, H. G., Nakata, J. K., Goodge, J. W., Reneau, S. L., John, B. E., and Hansen, V. L., 2000, Geologic map of the Mohave Mountains area, Mohave County, western Arizona., U.S. Geological Survey Miscellaneous Investigation Series 1-2308, 2 sheets.

Lucchitta, L, 1987, The mouth of the Grand Canyon and edge of the Colorado Plateau in the upper Lake Mead area, Arizona., in Beus, S. S. (editor), Rocky Mountain section of the Geological Society of America, Centennial field guide, 2, p.365-370.

Matty, D. J., 2006, Campus landscaping by constructing mock geologic outcrops, Journal of Geoscience Education, v. 54, p. 445- 451.

Miller, J. M. G. and John, B. E., 1999, Sedimentation patterns support seismogenic low-angle normal faulting, southeastern California and western Arizona., Geological Society of America Bulletin, v. 111, p. 1350-1370.

Nielson, J. E. and Beratan, K. K., 1990, Tertiary basin development and tectonic implications, Whipple detachment system, Colorado River extensional corridor, California and Arizona., Journal of Geophysical Research, v. 95, p. 599-614.

Wenrich, K. J., Billingsley, G. H., and Huntoon, P. W., 1996, Breccia-pipe and geologic map of the northwest part of the Hualapai Indian Reservation and vicinity, Arizona., U.S. Geological Survey Geologic Investigations Map 1-2522, 16 p. (2 sheets).

Doyle C. Wilson

Lake Havasu City, 2330 McCulloch Blvd., Lake Havasu City, Arizona 86403,

wilsond@lhcaz.gov

Timothy Montbriand

Mohave Community College, 1977 W. Acoma Blvd., Lake Havasu City, Arizona

86403, tmontbriand@mohave.edu

Copyright National Association of Geoscience Teachers Mar 2008

(c) 2008 Journal of Geoscience Education. Provided by ProQuest Information and Learning. All rights Reserved.