Arizona Bureau of Geology and Mineral Technology

IELDNOTE...............Fall 1985

by H. Wesley Peirce

Principal GeologistArizona Bureau of Geology

and Mineral Technology

Because Arizona is a land of geologic.~..:iiversity, it is blessed with a kaleidoscope of.ascinating landscapes. The resulting variety

of ecologic habitats is reflected in the State'sunusual array of flora, fauna, and land uses.

Physiography, or lay of the land, becauseof its wide impact, is a fundamental aspect of

the earth and its political subdivisions. Formore than 80 years, geologists and geogra­phers have been defining and redefiningArizona's basic physiographic attributes.Peirce (1984) reviewed these schemes and,based upon an updated geologic understand­ing, suggested further modifications. Whereasall schemes recognize that Arizona containstwo of the major physiographic provinces ofthe western United States, they differ on howto define a boundary qetween them. One ofthese large provinces, the Colorado Plateau(CP), occupies parts of four states,including

Figure 1. A southerly view into the mountainousterrain of the Transition Zone from the edge of theColorado Plateau province (Mogollon Rim).

the northeastern half of Arizona. The other,the Basin and Range (BR) province, involveseight states and occupies much of the south­western part of Arizona. Most geologists havenot continued to support this simple bipartitesubdivision in central Arizona because theydo not believe that it conveys the true natureof the central part of the State. The answerseems to be the recognition of a transition.

Figure 2 (above). Boundaries of physiographic provinces in Arizona, as suggested byPeirce, /984.

Figure 3 (top right). Looking northeast across BartleLL Reserooir on the Verde Rivertoward Mazatzal Peak, the highest point in the Transition Zone at 7,888 feeL The SierraAncha, on the skyline at righL is within the Transition Zone.

Figure 4 (bottom right). A northerly view into the Transition Zone showing SaguaroLake on the Salt River, the Superstition volcanic field in right center, and Four Peaks(elevation: 7,657 feet) in the snow'capped Mazatzal Mountains. The roclcs of theMazatzal Mountains are among. the oldest known in Arizona.

i,I

Peirce (1984) suggested that an expanded,formally defined Transition Zone (TZ) beconsidered in subdividing Arizona physio­graphically (Figures 1 and 2). This articleassesses the importance of the TZ and suggeststhat it be recognized as one of the State's threebasic physiographic subdivisions,

Definition and General Characteristics

Any definition of the TZ must consider thetwo major provinces that flank it. The classicCP and BR provinces differ markedly in theirgeologic and topographic attributes. Simplyput, the BR region has been severely brokenby geologic processes, whereas the CP regionhas not. This contrast can be easily observedon any State map that depicts geology ortopography,

The TZ trends northwest and its northernboundary with the CP is the Mogollon Escarp­ment, commonly known as "the Rim." Itssouthern boundary with the BR country ismarked by the interface of extensive bedrockexposures with extensive, low-elevation, allu­vial desert basins or valleys. The TZ embracesan estimated 18,000 square miles, or about

16 percent of Arizona. It is 350 miles in lengthand averages 50 miles in width, It extendsfrom the Grand Wash Cliffs near Lake Meadto the New Mexico border and incorporatesportions of Mohave, Yavapai, Gila, Maricopa,Navajo, Graham, and Greenlee Counties. Itincludes what has been informally called thecentral mountain region. Its highest point isMazatzal Peak at 7,888 feet above sea level(Figure 3) and its lowest is about 1,500 feetnear the confluence of the Verde and SaltRivers.

Although much of the TZ is more than amile high, its average elevation is intermediatebetween the higher plateau rim and the lowersouthern desert basins. The topography ismagnificently diverse and features deep can­yons (Salt River), high peaks (Four Peaks;Figure 4), and a myriad of interspersed mesas,valleys, and small mountains.\ Because itcontains topographic aspects of both the CPand BR provinces, the TZ actually bears littleresemblance to either.

The TZ is the surface-water province ofArizona (Figures 3 and 4). The Mogollon Rimis a drainage divide and topographic impedi­ment that, together with the TZ, stimulates

precipitation by forcing the prevailing northerlyflows of warm, moist air to higher, coolerelevations. Much of the precipitation (rain andsnow) from storms falls within the TZ drain-age area, where surface runoff is augmentedby immediate rainfall and snowmelt or bydelayed runoff (spring flow). The TZ, beinglargely a region of bedrock and steep streamgradients, tends to promote surface flow andinhibit wholesale infiltration into the subsur­face. Consequently, rapid rises in streamfloware the dominant natural hazard. Phoenixstands in a low desert basin that is bisectedby the Salt River, the major drainage in theadjacent TZ. Plans are being made to createadditional flood-control reservoir capacityupstream in the TZ on both the Verde andSalt Rivers. These surface waters also providerecreational outlets. Thousands of boaters,swimmers, and fishermen take advantage ofTZ waters every year. The zone contains sixlarge reselVoirs, including Roosevelt Lake­Arizona's largest self-contained water body...

The contrast of the TZ with flanking regionsis also expressed in the vegetation (Universityof Arizona, 1963). Chaparral and juniper­pinyon-oak woodland, typical of intermediate

FIELDNOTES, Fall 1985

"'"I"--------------------------------~----------~--~~-- ---

11~ fault, arrows show relative sense of movement

Figure 5. Schematic diagram shOWing present structural highness ofPrecambrian rocks in the Transition Zone (7Z)with respect to the acljacent Basin and Range (BR) and Colorado Plateau (CP) physiographic prouinces. The '/\"Datum is the contact between Precambrian (oldest) and Paleozoic (younger) rocks in the CPprouince; the "B" Datumis the contact between Precambrian and Tertiary (younger) rocks in the BR prouince.

ment). Elevations of this reference contactare 1,600 feet below sea level beneath BlackMesa in northeastern Arizona; 3,000 feetabove sea level at the Grand Canyon; 5,000feet above sea level at the TZ-CP boundary;and some unknown amount above 7,900feet at Mazatzal Peak in the TZ. The elevationof the reference surface at Mazatzal Peak isunknown because erosion has removed theoverlying Paleozoic rocks and an unknownthickness of Precambrian rocks. The eleva­tional extremes (-1,600 and +7,900) differ byalmost 10,000 feet. Unlike the Grand Canyon,where the datum is beneath 4,000 feet ofnearly flat-lying sedimentary rock, the datumon Mazatzal Peak is above the surface and isat least 5,000 feet structurally higher than atthe Grand Canyon. This reference surface isalso 2,000 feet higher at the plateau marginthan at the Grand Canyon, and at least 3,000feet higher at Mazatzal Peak than at theplateau margin. All data lead to the conclu·sion that presently there is a southerly rise inregional structure that culminates within theTZ. This rise exists because certain rockstrata in the CP are warped and gently tilteddownward toward the northeast (Figure 5).Geologic evidence indicates that some of thistilt was imposed prior to 90 million years(m.y.) ago when these CP rocks were muchlower in elevation than they are now.

Mazatzal Peak represents the maximumelevation of Precambrian rocks in the TZ.Even the lower surfaces on these old rocks,for the most part, are at higher elevationsthan the same rocks beneath the CPo Overall,this elevational difference renders the Pre·cambrian rocks of the TZ structurally higherthan those in the CP and helps to explain whythese oldest rocks appear at the surface inthe TZ. It also explains why the classic GrandCanyon sedimentary rock sequence of Paleo·zoic age is absent in the Phoenix ithas been eroded fromonce were, stnJcturclllynowisor~nrA\ll~'C con,ditionmuch of hi9t1rit~ss,

Structural Processes

Terrain differences are direct indicators ofgeologic differences. The State's three physio­graphic regions reflect three contrasting setsof geologic conditions. The most fundamentalphysical parameter that controls these differ­ences is "structure."

"Structure" is a term that describes theregional arrangement and geometric shapes(architecture) of rock masses. Rock massescan be unaffected, pulled, pushed, bent,broken, tilted, raised, and lowered to varyingdegrees and on different scales. The olderthe rock mass, the more likely it is to haveundergone one or more episodes of struc­tural disruption. An area's structural historycan be determined by making systematicobservations and interpretations of rock posi­tions. Many geologists have contributed tounraveling Arizona's geologic history, andmuch contemporary geologic research isdevoted to a better comprehension of itsstructural character.

The earth's surface features are the resultof interaction between internal and externalforces. These forces operate unequally, creat­ing irregularities on the earth's surface. Struc·tural disruption causes surface highs andlows. Once differential elevations exist, otherphysical and chemical processes (e.g.,weathering, transport, and deposition) beginto attack the highs and fill the lows in aneffort to regain a planar surface of equilibrium.Structural highness (uplift) brings older rockscloser to the surface. This is why Arizona'soldest rocks are so well exposed in the TZ.

Relative structural highness can be easilyidentified by noting the elevations of traceablereference surfaces. One such surface in theCP province is the contact between the Pre­cambrian and Paleozoic rocks near thebottom of the Grand Canyon. This contact orinterface CA" Datum; Figure 5) has beenpenetrated in deep drill holes elsewherebeneath the plateau surface and resurfacesnear the TZ-CP boundary (Mogollon Escarp-

elevations, are dominant. Ponderosa pinesoccupy islands of higher elevation and desertscrub occurs in small areas of low elevation.

~cause of limited soil distribution and waterWavailability patterns, agriculture IS negligible

in the TZ. Cattle ranching, however, issignificant.

Wildlife populations, taking advantage ofTZ life-supporting attributes, also tend to bedistinctive. Some of the best bear habitat inthe western United States is found in the TZ,and Arizona's largest antelope herds thrive inits northwestern section. Most of the bald­eagle nesting pairs in the State take advan­tage of riparian strips along its perennialwaterways. An otter reintroduction programby the Arizona Game and Fish Department isunderway in the lower Verde River section ofthe zone.

Rock and mineral attributes of the TZ areunique in several respects. The Tl, as will beexplained later, has the most extensive displayof Arizona's oldest rocks, rocks that give theregion much of its bold character. In Arizona atype of ore deposit known as a "massive-sulfidedeposit" is associated only with these oldestPrecambrian rocks, which are about 1.8 billionyears (b.y.) in age. Unlike the more famousporphyry coppers, which are disseminated,low-grade deposits, massive-sulfide deposits,such as those found near Jerome, are com­pact and high grade. The Verde mineraldistrict, which includes Jerome, yielded ores(largely copper, zinc, and silver) valued at

A':$3.5 billion at today's metal prices. TypicalW'porphyry copper deposits occur at Bagdad

and near Prescott, and gold placers in thePrescott region attracted early interest. Ninety­five percent of the mercury produced in Arizonacame from a cluster of mines in the MazatzalMountains district. Numerous small uraniumdeposits, some of which were exploited, areknown in the Sierra Ancha and adjacentregions. The expanse of Precambrian rocks inthe TZ, their relationship to early growth of thecontinent, and their mineralization make thema target for ongoing research and exploration.

Significant deposits of nonmetallic materialshave also been found in the TZ. A narrow,northwest-trending belt of good·grade, lowerPaleozoic (which overlies the Precambrian)limestone crops out in the northwest part.Umestone from this belt supports a large limeplant just east of Peach Springs, as well as acement plant in the Verde Valley that todaysupplies much of Phoenix's cement, but wasfirst built to supply cement for Glen CanyonDam. A salt deposit in the Verde Valley wasmined by Indians. Some of the highest qualitychrysotile asbestos in North America wasmined from the Sierra Ancha-Salt River region.Schist used as decorative facing stone isquarried near Mayer.

Fourteen of the State's 49 wilderness areasare within the TZ. In other words, the TZ,e which contains 16 percent of Arizona's totalacreage, contains nearly 30 percent of itswilderness areas, a proportion that clearlyindicates this area's relative remoteness andunusual qualities.

~I

FIELDNOTES, Fall 1985

---------------------------------------------~==~-----~---~---------~-~--------.....

Figure 6. Looking north into the Transition Zone. Flat-topped, eroded mesas are capped by the lava (volcanic rocks)of "B" Datum (see Figure 5). Although locally the lavas overlie slightly older sedimentary materials (whiteforeground), they generally overlie Arizona's oldest rocks. The sediments and volcanics. which are about 15 to 17m.y. old, are believed to have accumulated in a previously existent erosional valley. They are now being destroyedby a conlinuing episode oferosion. Drainage is to the south into the topographically lower country of the Basin andRange province.

past and present, promotes erosion.A reference surface is also needed for

structural comparison of the TZ with the BRprovince to the southwest. The sedimentaryrocks used as a reference surface in the CPprovince have been eroded away in the BRprovince, Although Precambrian rocks arepresent in the BR region, they tend to becovered by much younger rocks than in theCP region to the north. The contact betweenthe Precambrian rocks and these youngerrocks serves only as a reference surface forinterpretation of events that have happenedsince the development of these youngerrocks ("B" Datum, Figures 5 and 6),

One of the characteristics of the BRprovince is the expanse of low-elevation desertvalleys or basins, Drill samples and otherinformation indicate that deep structuralbasins commonly underlie the low desertsurfaces. Relative to the TZ, these basins aredowndropped along faults. Available dataindicate that downdrops of 6,000 to 8,000feet are not unusual; displacement may be asmuch as 10,000 feet in some areas. ParadiseValley north of Phoenix, for example, repre­sents a BR basin adjacent to the TZ. A drillhole at the north end of the basin wasstopped above the younger reference datumat an elevation of 3,676 feet below sea level.To the north near Carefree, the outcroppingdatum at the edge of the TZ is at an elevationof 2,500 feet above sea level (Figure 6), Theminimum structural differential of these twopoints, therefore, is about 6,000 feet, with thebasin floor as the low point and the TZoutcrop as the high point. The causal mech­anism for this structural disruption is faulting.A minimum differential of more than 11,000

feet, however, exists between Precambrianrock in the Paradise Valley basin of the BRprovince (-3,676 feet) and Precambrian rockat Mazatzal Peak in the TZ (+7,900 feet).Faulting accounts for 6,000 feet; the remain­ing 5,000 feet that is confined to the TZ itselfwas inherited prior to the BR faulting eventand is subject to investigation of the actualcause(s) of this internal differential.

The time span between "A" Datum and"B" Datum represents a missing record ofabout 500 m.y, in the Phoenix and TZ regionswhere all Paleozoic and Mesozoic strata areabsent. Where this missing record prevails,there is no simple way of reconstructing all ofthe structural movements that have affectedthe very old crystalline rocks. The only con­clusions to be drawn here might be these: (l)in the CP, the older "A" Datum was tilted sothat structural highness prevailed to the south;and (2) "B" Datum shows that there isconsiderable differential elevation, much ofwhich is caused by faulting that leaves the TZstructurally high relative to the flanking basinsin the BR province. The net result of geologichistory has been the creation of a TZ, which,because of its structural highness relative tothe CP and BR province basins, featuresextensive exposures of Arizona's oldest rocks(Figure 5).

Erosional Events

Two basic processes create differences inland elevation: (l) structural processes, orthe differential movement of rock masses, asdiscussed earlier; and (2) erosion, whichcauses local land-surface differentials. The

local relief caused by erosion in the GrandCanyon exceeds 4,000 feet. This local relief,however, could not exist if there were noregional structural differential to induce_erosion (I.e., if there were no regional relief to.cause the river to downcut). Where surfacerelief is involved, therefore, caution is neededin assigning immediate causal factors, This isespecially true of the TZ, where spectacularsurface irregularity is characteristic. Thecomplex, rugged terrain results from anincompletely understood history that includesmultiple structural and erosional events.Whatever the details, the TZ is now, from astructural point of view, the backbone ofArizona (Figure 5).

The TZ is geologically unique because itpreserves a geologic record that has not beenfound in the larger provinces that bound it. Animportant aspect of this record is the preser­vation of evidences of ancient erosion thatindicate a complex history of terrain develop­ment. Because structural and erosional eventsare closely related, erosional events can be akey to recognition of causal structural events.Another clue to a structural happening, asalready mentioned, is an out-of-place datum.A good example is the occurrence of fossilmarine oysters and clams at 7,000 feet abovesea level along the edge of the CP near ShowLow. The enclosing sandstones, believed tobe about 95 m,y. old, were deposited in ashallow sea that covered much of northernArizona and adjacent states. Based on thebelief that sea level at that time was notegreatly different than at present, most geolo- ­gists would say that the fossils have beenuplifted and the CP province structurallyraised several thousands of feet sometimeduring the last 95 m.y. A question remains,however: what was uplifted when? This isreally two questions and neither lends itself toeasy answers. In Arizona, such answers can-not be found in the CP province; rather, theymust be sought in adjacent regions, especiallythe TZ, The TZ, as discussed earlier, wasuplifted more than the CP; the "what" ques-tion must therefore include the TZ as well.

The TZ, as already stated, contains a com­plex and fascinating erosional history thatnecessarily reflects a complex history of struc­tural movement. An erosional history, suchas one that is reflected in the Salt Riverdrainage system, might be related to themajor regional uplift that drove the seas fromArizona and left the oysters high and dry,

Much of the Salt River flows within the TZ.This drainage system can be divided intosegments that differ markedly in terraincharacteristics. The 18-mile-long segmentbetween Canyon Creek to the northeast andLake Roosevelt to the southwest, in which theriver flows southwest, is especially intriguing.Relief between the river and the regional highpoint in the adjacent Sierra Ancha (Aztec_Peak - 7,694 feet).is ~bout 4,700 feet. This is_;more than the relIef In the Grand Canyon at ­El Tovar on the south rim,

Upstream from Canyon Creek is the morefamiliar Salt River Canyon segment that is

FIELDNOTES, Fall 1985

Figure 7. Map depicting contrasting forms of two canyon segments occupied by the Salt River in the Transition Zone;the Canyon Creek fault is the boundary between the two segments. Shading ofelevations below 5,000 feet illustratesthe comparative widths and contours the overall relief. See Figure 8 for faulting history.

possible to delimit with certainty the largerzone that was affected. The rock units thataccumulated in the bottom of the paleo·canyon are the same as those that overlie thelarge copper deposits in the Miami, Globe,and Ray areas, It seems likely, therefore, thatthe uplift-erosion episode that produced thepaleocanyon may have also caused theunroofing of these ore deposits. Young (1982)postulates that 180 miles to the northwestother TZ paleocanyons, also with 4,000 feetof relief, were eroded by north·flowing drain·age. Dating methods indicate that these paleo·canyons and the Sierra Ancha segment aresimilar in age. Such evidence suggests thatthe TZ was once even structurally higherthan it is today and that it has founderedsince its heyday.

This structural information from the TZenables further interpretation of the oysterfossils at 7,000 feet along the southern edgeof the adjacent CP province. It seems probablethat their structural position was influencedby an uplifting event that induced canyon·cutting in the TZ during and after formationof the youngest of the nearby copper deposits(59 m.y. ago) and before rock units began toaccumulate on the irregular erosional surface30 m.y. ago.

Conclusion

A Transition Zone, in one form or another,deserves to be recognized as one of Arizona'sthree basic physiographic subdivisions. Pro·portionally, its contributions to the State(water, wildlife, scenery, wilderness, recrea·tion, minerals, etc.) far exceed its size. Its

5

30 - 59 MILLION YEARS AGO

C'''ONc"m~FAULT

15 MILLION YEARS TO PRESENT

not unusual. In any given locality, earthstresses and their manifestations vary throughtime. The early indication of pre·30·m.y. upliftcited here is based upon local evidence.Although a much larger region undoubtedlyunderwent structural adjustment, it is not yet

Figure 8. Block diagrams illustrating how two episodesof movement on the Canyon Creek fault influenceddrainage development and canyon styles along thecourse of the Salt River. (See also Figure 7.)

B

A

for establishing this ideapal!eotol=)ogra~)hy in the Sierra Ancha

laid by N. H. Dartona most perceptive field

clearly diagrammeddid not discuss ortheir implications.

(1959)paleo1carlyon relationships,

discussed them.el«)lallation fnr th""p uninterpreted

d!:)SerYClti§flg that they werethe time. Had

of present·would prob·

Clntiquityberlind these~~'~'L""J,~impressed

irnportalot struc·subse·

establlish itself, Thisside left the east

prc)mote~d the youngercharacterizes thesegment (Figure

crossed by State Highway 77 between Globeand Show Low. Because of the low width·to·depth ratio, this portion is impressive com·

.pared to the Sierra Ancha segment, which"h,as twice the relief, but is also much broader

(Figure 7). Why are there such form differ·ences in adjacent segments of the sameriver?: they have contrasting pre·Salt Rivergeologic histories. Evidence now indicatesthat the shallower and narrower west·trendingSalt River Canyon segment was carved bythe Salt River since 12 m.y. ago. In contrast,the deeper and broader southwest·trendingSierra Ancha segment has a notably earlier

of canyon-eutting (prior to 30 m.y.river that drained towards the

opposite to the present flowfirst expressed by Peirce,

---------------------------~----~-----~-===-"'-------~---~-~--------...

magnificent ruggedness and related inacces­sibility stem largely from a complex andpoorly understood structural and erosionalhistory. Because of its central position andbecause, in a structural sense, the ColoradoPlateau and Basin and Range provinces nowtend to fall away from it, the Transition Zonequalifies as Arizona's "backbone." Furtherresearch in the Transition Zone could signifi­cantly aid understanding of the geologichistory of the Southwest in general andArizona in particular.

References

Darton, N. H, 1925, A resume of Arizona geology: ArizonaBureau of Mines Bulletin 119,298 p.

Finnell, T. L, 1962, Recurrent movement on the CanyonCreek fault, Navajo County, Arizona, in GeologicalSurvey research 1962, short papers in geology, hydrol­ogy, and topography, articles 1?0-179: U_S_ GeologicalSurvey Professional Paper 450-0, p. 80-81.

Peirce, H. W., 1982, Cenozoic drainage reversal in theMogollon Rim area-a classic example: Unpublishedpaper presented at the 35th annual Symposium onSouthwestern Geology, Museum of Northern Arizona,Flagstaff.

--1984, The Mogollon Escarpment: Arizona Bureauof Geology and Mineral Technology Fieldnotes, v. 14,no. 2, p. 8-11.

University of Arizona, Agricultural Experiment Station ancaCooperative Extension Service, 1963, Arizona natura.vegetation: Bulletin A45 (Map), scale 1:1,370,000.

Wilson, E. D., Moore, R. T., and Peirce, H. W., 1959,Geologic map of Gila County, Arizona: Arizona Bureauof Mines, scale 1:375,000.

Young, R. A., 1982, Paleogeomorphic evidence for thestructural history of the Colorado Plateau margin inwestern Arizona, in Frost, E. G., and Martin, D. L, eds.,Mesozoic-Cenozoic tectonic evolution of the ColoradoRiver region, California, Arizona, and Nevada: SanDiego, Cordilleran Publishers, p. 29·39.

LANDSCAPES OF ARIZONA

"The 295,146 square kilometer surface ofArizona contains some of the most striking,varied, and beautiful landscapes that can beformed by geologic and climatic processes.Although the surface of the state has beenquiescent at times, more often it has under­gone compression, stretching, uplift, andsinking. These processes have created tower­ing mountains, sheer massive scarps, anddeep basins and canyons. Violent eruptionsof lava or rock fragments or smoothly flowinglavas from volcanos have added to landscapeformation. At different locations within thestate, one can see exposures of every type ofrock from the finest and softest silts and claysto the hardest crystallines. Minerals in certainexposed rocks present drab colors in someareas or a vivid kaleidoscope of colors inothers.

"Climates over the state that helped moldthe landscape have been and still are asvaried as the landscapes themselves. In thepast, as today, parts of the state have hadlong, monotonous, hot, dry summers. At thehigher elevations, however, the winters werecold and bitter; the cold at times was suffi­cient to form mountain glaciers which slowlyground their way down valleys. Not alwayswere the skies clear. During many of theviolent volcanic eruptions, huge quantities ofdust and ash clouded the air many kilometersaway from the craters, and associated obnox­ious to lethal gases drifted with the winds. Attimes the skies were filled with dust and sandas strong winds carried these materials toevery part of the state.

"What we see today is the end result of

millions of years of nature's activity. The dryclimate of Arizona has helped keep thesesharp, vivid landscapes exposed by notweathering the rock to where it could form adeep, protective cover of soil and otherdepositional materials .... The beauty of thelandscape needs no qualification and can beappreciated with no further geological investi­gation. However, people are inquisitivecreatures and often wonder-Why is thatmountain or canyon there? Why are theserocks so red and those rocks so black? Whyare some rocks evenly stratified and somevery massive and crystalline? Many other

NOW AVAILABLE5 X 7 postcard on the

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such questions occur to the observer of thelandscape; undoubtedly the answers to suc~equestions will enable the observer to experi­ence a greater satisfaction than that of simpleaesthetic appreciation."

The preceding text is excerpted from thepreface of Landscapes of Arizona-theGeological Story, a recent book publishedby the University Press of America and editedby 1. L. Smiley, J. D. Nations, 1. L. Pewe, andJ. P. Schafer. This 505-page volume sum-marizes geologic work that pertains tointerpretation of landscape development inArizona. In preparation for 10 years, thebook comprises 17 chapters, each writtenby one or more geologists experienced inworking on Arizona geology. The semitech-nical material is accompanied by a glossary,which explains terms that may be unfamiliarto the layperson. Basic principles and con-cepts of landscape formation are discussedin the text, as well as specific types oflandforms in certain areas of the State.Topics include Cenozoic plant and animalfossils, climatic changes during landformdevelopment, volcanic landforms, glaciation,\~eolian (wind-formed) landforms, plateaus, !~.canyons, alluvial fans and pediments, desert UJbasins, etc. Numerous photographs andseveral maps are included to illustrate andlocate various geologic features in Arizona.

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FIELDNOTES, Fall 1985

Geological Survey Branch Hosts21st Forum on the Geology of Industrial Minerals

by H. Wesley Peirce

The 21 st Forum on the Geology of Indus­trial Minerals, held in Tucson April 9-12, 1985,was hosted by the Arizona Geological Survey(AGS), the Geological Survey Branch of theArizona Bureau of Geology and Mineral Tech­nology. The 21 st forum boasted a recordattendance: 154 participants (not including28 spouses) represented 28 states, Canada,and Mexico. Non-Arizonans composed 75percent of the total number of registrants, apercentage that clearly demonstrates thenational and international character of theforum.

The term "industrial minerals" is synony­mous with "nonmetallic minerals and rocks."In most states it is the industrial minerals, ornonmetallics, that dominate the mining

industry. In a few western states such asArizona, the nonmetallics, though vitallyimportant, play second fiddle to the metals.

The earth is a storehouse of common,relatively cheap materials suitable for con­struction and other uses. The bulk of theNation's cities, homes, and streets is con­structed from· mined and processed non­metallic materials. In the East and Midwest,many geologists are employed by industrial·mineral firms. Because of the basic impor­tance of nonmetallic materials, Bob ("TheGeologic Column") Bates, while a professorat Ohio State University, organized the firstannual forum as a place where industrial·mineral geologists and engineers could meetto share observations, problems, and insightsin an atmosphere of friendly informality(Figure 1).

The program in Tucson featured five field

trips for registrants and spouses, 23 technicalpapers,'and a banquet with after-dinner pro­gram. An independently arranged, postmeet­ing float trip on the Colorado River wasoffered to registrants and their spouses.Thirty-seven persons took advantage of thisrare opportunity.

PREMEETING TRIPS

Two premeeting trips were offered to regis­trants and their spouses. The main trip-was avisit to zeolite deposits; the second trip pro­vided an opportunity to view an open-pitcopper-molybdenum mine.

Under the leadership of Ted and Dan Eyde(Tucson industrial-mineral consultants), 70persons piled into vans for a trip to Bowie toview the largest chabazite (a zeolite mineral)deposit in the United States. Highlights of this

Figure 1 (right). Larry Fellows (left), State Geologist and Assistant Director of theArizona Bureau of Geology and Mineral Technology, and Wes Peirce (center),Principal Geologist at the Bureau and General Chairman of the 21 st Forum, conversewith Bob Bates (right), Professor Emeritus at Ohio State University and founder oftheForum on the Geology of Industrial Minerals.

-FigUre 2 (bottom teft). Zeolite (chabazite) pit near Bowie, Arizona. Overburden isremoved to expose 6-inch-thick "are" horizon (see Figure 3). Chabazite is stockpiledand trucked to the railroad as needed.

Figure 3 (bottom right). Six-inch-thic!c, high-grade chabazite deposit is overlain byimpure beds.

FIELDNOTES, Fall 1985

excursion are shown in Figures 2 and 3.Another van load left for the Duval Sierrita

copper mine, where Dan Aiken, chief mininggeologist, took visitors into the pit for a closelook at ore. They later drove through the millcomplex and viewed the mineral-concentrationprocess. The timing of this visit was oppor­tune because mine production had justreached an all-time high. Duval Corporation'sDean Lynch and Dan Aiken were responsiblefor making this experience possible.

TECHNICAL SESSIONS - APRIL 10

Morning

After brief opening remarks by the generalchairman (Wes Peirce), the group was offi­cially welcomed to Arizona by Dr. Richard A.Swalin, Dean of the University of ArizonaCollege of Engineering and Mines and Direc­tor of the Arizona Bureau of Geology andMineral Technology. Dr. Larry Rooney, U.S.Geological Survey, chaired the morning ses­sion, which included one overview and sevenregional papers.

Jim Dunn (Dunn Geoscience Corporation)presented the first paper, "Mining and theEnvironment-Finding Common Ground."Jim perceives that there is a "war" going onin the technologic, philosophic, and politicaltrenches between mineral-industry and envi­ronmental leaders, a war to which much ofthe public is oblivious. Despite this battle, hebelieves that there are goals common toboth factions, goals that all reasonable andcaring individuals can seek and attain. Jimsuggests that the environmental fervorexpressed by well-intentioned idealists hasbeen promoted and perpetuated in thiscountry by media hype. He also thinks that,in response to the demands of reasonable

Figure 4. Ken Santini. Anaconda Minerals Company,talks about euaporite deposits in California.

persons, a wave of credibility is developingthat will replace environmental extremismwith basic, well-balanced information. Thoseassociated with the mineral industry, Jimsuggests, can help further this dialogue andsharing of scientific data by encouraging thepromoters of good sense as they handleissues rendered controversial by the media.

Steve Reynolds (AGS geologist) empha­sized that geologic framework controls theexistence and distribution of all mineral androck deposits. He discussed highlights ofArizona's geologic history of 1.8 billion yearsand explained how useful earth materialsassociate with geologic events that occurredduring that time. He pointed out that much

Figure 5. Malcolm Ross, U.S. Geological Suroey,discusses "asbestos" and the public health issue.

of Arizona, geologically speaking, remains afrontier that has significant potential for theoccurrence of unrecognized earth materialsuseful to mankind.

Wes Peirce (AGS geologist) talked aboutArizona's industrial (nonmetallic) minerals androcks. He reminded the participants that in1981, Arizona was ranked number one in theNation with respect to the value of nonfuel­mineral production ($2.56 billion). About 7.5percent of this value, or $192.5 million, can beattributed to nonmetallic products. In thissame year, at least 225 industrial mineral androck deposits were being worked to produceabout 10 tons of material per Arizona resident.Many of these "bread-and-butter" materials(cement, lime, sand, gravel, stone, salt, clays,etc.) are fundamental to the constructionindustry. Consequently, product demand isdirectly related to population growth andeconomic strength. Growth in the Arizonasun-belt dictates concomitant growth in theproduction of fundamental industrial-mineral

commodities.Keith Papke, Nevada Bureau of Mines and

Geology, summarized industrial-mineral pro·duction in Nevada and Bryce Tripp, Utar_Geological and Mineral Survey, gave a simila.orientation for Utah. Joaquin Ruiz, Depart­ment of Geosciences, University of Arizona,summarized Mexico's industrial-mineral pro­duction. Rounding out the regional story,Steve Kupferman, Kaiser Cement Corpora­tion, discussed the geology of cement rawmaterials in Arizona and southern California.Howard Brown, Pluess-Staufer (California)Inc., talked about the stratigraphy, tectonicsetting, and industrial minerals of Paleozoicrocks in the Mojave Desert of California.

Afternoon

The second technical session, chaired byMichael N. Greeley, Arizona Department ofMines and Mineral Resources, featured ninepapers. Dennis Bryan, Engineering TestingAssociates, discussed natural lightweightaggregates of the Southwest. Gerald Allen,The Earth Technology Corporation, outlinedan approach to locating high-quality aggre­gates in the Basin and Range province. KenSantini, Anaconda Minerals Company, pro­vided a geologic evaluation of a brine­saturated evaporite deposit in the southernportion of Searles Lake, California (Figure 4).

Rules and regulations governing mineraldevelopment are fundamentally important.!and two papers focused on this subject_Terry Maley, U.S. Bureau of Land Manage­ment, talked about acquisition of federallyowned industrial minerals; and EdwardSpalding, Arizona State Land Department,discussed mining industrial minerals onArizona State Trust lands.

The media frequently place health·relatedmatters before the public. Malcolm Ross,U.S. Geological Survey, talked about mineralsand health as related to the "asbestos"problem (Figure 5). Dr. Ross, one of the"promoters of good sense" to whom JimDunn referred in his talk, confronts thefront-page issue of "asbestos" with scientificdata and analysis often neglected by mediapersonnel.

Two additional papers ended a productiveafternoon session: Mark Bowie, New MexicoBureau of Mines and Mineral Resources,compared zeolite deposits in Arizona, NewMexico, and Texas; and John Welty, Univer-sity of Arizona graduate student and AGSresearch assistant, discussed the geologyand industrial uses of Arizona's volcanicrocks. John emphasized the importance ofpast volcanic processes in making usefulproducts. Furthermore, he concluded thatpotential is high for recognition and develop­ment of new deposits of useful volcanicII\,materials. .J

Concurrent with the technical sessions,Maxine Peirce guided two van loads of spousesto the Arizona-Sonora Desert Museum and theSan Xavier Mission (Figure 6).

FIELDNOTES, Fall 1985

e.

. Figure 6 (right). Spouses of forum attend.. ees visit theission San Xavier del Bac near Tucson. The mission

:site was first established in 1700 by Fr. EusebioFrancisco Kino, the "Padre on horseback. " The presentchurch, which has often been described as the bestpreserved and most beautiful of all missions in theSpanish Southwest, was built between 1783 and 1797.

Figure 7 (bottom left). Abandoned gypsum quarrynear Winkelman in the San Pedro Valley. Bob Scar­borough. Arizona Geological Survey, discusses thegeology ofgypsum.

Figure 8 (bottom right), Field-trip participants considerthe environment in which the gypsum accumulated.

INTERIM ALL-DAY FIELD TRIPS

More than 100 persons loaded into busesand miscellaneous vehicles for the traditionalinterim, all-day field trip on April 11. This tripfeatured geology, scenery, and metallic andnonmetallic mineral operations. The routeincluded Oracle, Kearney, Superior, andGlobe. AGS geologists Steve Reynolds andBob Scarborough provided orientation onthe buses.

The first formal stop featured the center ofArizona's gypsum industry in the San PedroValley just south of Winkelman. A visit was

~~ade to a recently abandoned gypsum~uarry used by the Gold Bond Division of

the National Gypsum Corporation to manu-facture wallboard at a Phoenix plant (Figures7 and 8). Bob Scarborough, independentgeologist and part-time employee of the

FIELDNOTES, Fall 1985

AGS, gave an overview that emphasized thegeology of late Cenozoic basins and basin-fillsedimentary deposits in southern Arizona'sBasin and Range geologic province. TheSan Pedro Valley gypsum deposits areexamples of useful materials contained in abasin-fill sequence that accumulated about5 million years ago when camels and othervertebrates roamed the ancestral valley.

The second stop took advantage of aconvenient overlook of the Ray mine, anoperating open-pit copper mine owned by theKennecott Copper Corporation. The third stopfeatured the State's perlite mining center nearSuperior, where the host was the Sil-Flo Cor­poration. Ground and sized perlite is exportedand "popped" (expanded) elsewhere. Someof Sil-Flo's product, for instance, is used in thefiltration of beer made in Dallas, Texas. Partici­pants were given free time to collect Apachetears, which are semiprecious, dark-colored

nodules of volcanic glass. Mr. and Mrs. LouisLucero helped to make this a pleasant andinformative interlude.

The field trip continued through the QueenCreek Tunnel to a lunch stop at the Oak Flatspicnic area in the Tonto National Forest.After this welcomed respite, the trip pro­ceeded to an "asbestos" mill via the copper­mining towns of Miami and Globe. Here,forum attendees received a rare, first-handreview of the "asbestos" controversy fromsome of the principals involved in this on­going saga. Mr. D. W. Jaquay and his asso­ciates led a tour through their fully licensed,inoperative "asbestos" mill and providedsamples of some of the highest gradechrysotile asbestos fiber in North America(Figure 9).

Concurrent with this fieldgroup of forum attendeesMexico and the historic sites be'twE~en

Figure 9. Field·trip participants visit the inoperative "asbestos" mill in Globe. Arizona. Figure 10. Don Morris. Building Products Company,discusses vitrified clay pipe.

border town and Tucson. Both trips returnedto Tucson for the annual banquet. Aftergreetings and comments from persons atthe head table, Peter Kresan, geologist andnoted photographer, presented an originaltwo-screen slide program set to music,entitled "Arizona Images."

FINAL TECHNICAL SESSION

The last technical session, consisting ofseven presentations, was held the morningof Friday, April 12. Dr. Larry Fellows, StateGeologist and Assistant Director of theArizona Bureau of Geology and MineralTechnology, chaired the session. With oneexception, the program featured Arizona'sindustrial minerals: Leo Langland, ArizonaDepartment of Transportation, talked aboutlocating, sampling, and evaluating potentialaggregate deposits; Don Morris, BuildingProducts Company, gave an original paperon raw materials and the manufacture ofvitrified clay pipe in Arizona (Figure 10);Jerry Grott, Southwest Salt Company, dis­cussed solar salt in Arizona; Dan Eyde, GSAResources, Inc., talked about bentonite andspecialty sand deposits in the BidahochiFormation; Ted Eyde, GSA Resources, Inc.,discussed the Bowie chabazite deposit; JohnRains, California Portland Cement Company,completed the program with a talk on ArizonaPortland Cement Company's Rillito opera­tion. One paper, by R. E. Miques, BechtelCivil and Minerals, Inc., focused on aggregatefor large works, using examples from outsideArizona.

10

CLOSING COMMENTS

Like a speeding car, the 21st Forum on theGeology of Industrial Minerals has come andgone. It is difficult-to grasp and appreciate thetotal effort needed to conduct a successfultechnical meeting. Each presenter, attendee,vehicle driver, trip leader, and session chair­man must contribute. The record attendancewas, in large part, a tribute to the naturalattractiveness of Arizona. It took, however, thecontributions of many individuals, includingattendees, to render this meeting a candidatefor the "best-ever" forum. Maxine Peirceserved as treasurer, registration chairman,arranger of spouse activities, and trip leader.Evelyn VandenDolder produced the ProgramWith Abstracts, and Janet Christner compiledregistration lists and performed other tasks.Many others aided in myriad ways. The 20firms that generously donated to the socialfunctions also contributed to the success ofthis conference.

The Bureau has extra copies of the pro­gram brochure, which contains informativeabstracts of all 23 technical papers. Theseare available for $2.00 each. A proceedingsvolume will be published and available fordistribution sometime in 1986.

With the 21st annual forum at a close,Arkansas a'waits next year's meeting. AnyState interested in hosting a forum shouldmake plans so that an invitation can beformally extended at a future meeting. As ofthis writing, 1989 is the first unassigned year.(Illinois will host the 1987 meeting; Oregonwill probably host the forum in 1988.)

FIELDNOTES, Fall 1985

NEW BUREAU PUBLICATIONS

L

_ The following publications may be purchased over the counter orby mail from the Bureau offices at 845 N. Park Ave., Tucson, AZ 85719.Orders are shipped via UPS; street address is required for fastestdelivery. All orders must be prepaid by check or money order made outto the Arizona Bureau of Geology and Mineral Technology. Shippingand handling charges are listed below. If your total order is

$1.01 to $5.00, add $1.75 40.01 to 50.00, add 7.755.01 to 10.00, add 2.25 50.01 to 100.00, add 10.0010.01 to 20.00, add 4.25 More than 100.00, add 10%20.01 to 30.00, add 5.50 Foreign mail, add 40%30.01 to 40.00, add 6.25

BULLETIN

Welty, J. W., Reynolds, S. J., Keith, S. B., Gest, D. E., Trapp, R. A.,and DeWitt, Ed, 1985, Mine index for metallic mineral districts ofArizona: Bulletin 196, 92 p.; $7.00.

This index provides a county-by·county list of mines withinArizona's mineral districts, as defined in Arizona Bureau of Geologyand Mineral Technology Map 18 and Bulletin 194. Approximately5,500 mines are included. Two lists are given for each county: the firstis a catalog of mines within each district; the second is an alphabeticalcross-index of mines within the county. A mineral-district map of eachcounty, at a scale of 1:1,000,000, is also presented. This index allowsthe explorationist to determine which mines are responsible for themetallic mineral production recorded in Bulletin 194.

OPEN·FlLE REPORTS

Reynolds, S. J., and Spencer, J. E., 1984, Geologic map of the_ gUila RidgeBullard Peak area, eastern Harcuvar Mountains,

lvest·centraIArizona: Open-Pile Report 84-4,2 p., scale 1:24,000;$1.75.

The Aguila Ridge-Bullard Peak area contains the Bullard detach­ment fault, a major normal fault that separates lower-plate chloriticbreccia and mylonitic gneiss of the Harcuvar metamorphic corecomplex from an upper plate of highly tilted, Tertiary volcanic andclastic rocks. The Tertiary sequence includes welded ash-flow tuffs,sedimentary breccias, landslide-related megabreccias, and andesitesthat host copper-gold mineralization at the Bullard mine. This mapidentifies upper-plate faults and the Bullard detachment fault, whichare locally altered and mineralized.

Reynolds, S. J., and Spencer, J. E., 1985, Reconnaissancegeologic map of the Merritt Hills, southwestern Yavapai County,Arizona: Open-File Report 85-5, scale 1:24,000; $2.00.

This reconnaissance map depicts the Precambrian plutonic andmetamorphic geology of the small hills west of Congress Junction.

Spencer, J. E., and Welty, J. W;, 1985, Reconnaissance geology ofmineralized areas in parts of the Buckskin, RaWhide, McCracken,and northeast Harcuvar Mountains, western Arizona: Open·FileReport 85-6, 31 p.; $5.00.

This report is a catalog of brief descriptions of mines andprospects in most mineralized areas of the Buckskin and RawhideMountains, plus one mineralized area each in the McCracken andnortheastern Harcuvar Mountains. The descriptions are based on newfield observations. As a result of this field review, mineral-districtassignments for several mines have been modified and updated.

_ Reynolds, S. J., Rorence, P. P., Currier, D. A., Anderson, A. V.,W Trapp, R. A., and Keith, S. 8., 1985, Compilation of K-Ar age

determinations in Arizona: Open·File Report 85-8,320 p.; $24.00.This report summarizes information from a computerized compil­

ation of 1,214 published K-Ar age determinations in Arizona.lnforma­tion compiled for each date includes material dated, rock type, nameof rock unit, location information, and comments about the geologic

FIELDNOTES, Fall 1985

setting and significance of the date. The ages are indexed by geo·graphic area, geologic formation or rock unit, and original samplenumber. A complete list of cited references is included.

Spencer, J. E., Richard, S.- M., and Reynolds, S. J., 1985,Geologic map of the Little Harquahala Mountains, west-centralArizona: Open·Pile Report 85-9, 18 p., scale 1:24,000, 3 sheets;text: $3.00; map: $3.00

The Uttle Harquahala Mountains are composed of a series ofstacked thrust sheets that contain a diverse assemblage of rocks andstructures. The lowest exposed rocks are Mesozoic volcanic andsedimentary rocks equivalent to the McCoy Mountains Formation andunderlying Jurassic (?) volcanics. These units are structurally overlainby the Hercules plate, which is composed of Jurassic and Precambriancrystalline rocks. The Hercules plate is overlain by the Centennialplate, which contains Precambrian granitic rocks, a cratonic section ofPaleozoic rocks, and Mesozoic volcanic and sedimentary rocks. Themajor structures have been intruded by the Upper Cretaceous GraniteWash Granodiorite and numerous middle Tertiary dikes. Mineralizationin the area, including the bonanza gold ores of the Harquahala mine,is generally controlled by either thrust-related or post-thrustingstructures.

Wright, P. L., Trapp, R. A., Reynolds, S. J., Richard, S. M., andPeirce, H. W., 1985, Theses and dissertations on Arizona geology,1891-1978: Open-Pile Report 85-10, 141 p.; $12.00.

This report contains a comprehensive list of theses and disserta­tions, completed between 1891 and 1978 on Arizona geology andrelated subjects. The compilation includes a main list of theses anddissertations, alphabetized by author, and two supplementary indexes.The first index is a statewide subject index, which lists the author, date,and physiographic-geologic province or provinces (Colorado Plateau,Transition Zone, or Basin and Range) encompassed by each thesisand dissertation. The second index lists the author and date of eachthesis and dissertation by province, county, and specific geographicarea (e.g., San Francisco volcanic field or Sunset Crater).

Spencer, J. E., Reynolds, S. J., Anderson, Phillip, and Anderson,J. L., 1985, Reconnaissance geology of the crest of the SierraEstrella, central Arizona: Open-File Report 85-11, 20 p.; $4.00.

A reconnaissance study of the crest of the northwest-trendingSierra Estrella in central Arizona indicates that this range is primarilycomposed of gneiss and schist with a steeply dipping, northeast­striking foliation similar to that in 1.6- to 1.7-b.y.-old metamorphicrocks found elsewhere in Arizona. Granitic rocks with a concordantfoliation form sills and large intrusions into the schist and gneiss andare thought to be approximately the same age as metamorphism anddeformation. Younger, weakly foliated to unfoliated granitic rocks areexposed at the south end of the range and correlate with the wide­spread l.4-b.y.-old granite suite of North America.

Welty, J. W., Reynolds, S. J., and Trapp, R. A., 1985, Ore gradesfor metallic mineral districts ofArizona: Open·File Report 85-12,34 p.; $6.00.

This report presents the results of a computerized compilation ofore grades for metallic mineral production in Arizona. The grades forall recognized mineral districts are presented by county. Mineral dis·tricts have also been classified according to 10 distinct deposit types,and characteristic grades for each deposit type have been calculated.Variations in metal content within a single deposit type have beenexamined by normalizing production figures for each mineral districtto the total production for all mines of that deposit type.among different deposit types can be compared by nOlrffii:llizingproduction of each mineral district to total base- and pn~dou:s-n1etal

production in Arizona. The normalized data are thendiagrams with gold, silver, and total base-metal pr<)dllctionapices.

11

Orlo Childs Retires from MMRRI

Dr. arlo E. Childs, director of the ArizonaMining and Mineral Resources ResearchInstitute (MMRRI) since 1980, retired as ofdune 30, 1985.

Dr. Childs brought to this position extensiveexperience in petroleum exploration, geologicresearch, teaching, and educational admini­stration. He received his B.S. and M.S. degreesfrom the University of Utah and his doctoratein geology from the University of Michigan.He taught at Weber College, the University ofMichigan, Colgate University, the Universityof Wyoming, and Texas Tech University. Dr.Childs served as a geologist for the SinclairWyoming Oil Company and as ExplorationProjects Director for the Phillips PetroleumCompany. In the latter position, which heheld for 13 years, he planned and directedthe work of 45 geologists in the UnitedStates, Canada, Central America, Australia,Algeria, and Libya.

Dr. Childs launched the research programin oceanography for the U.S. Geological Survey(USGS). He directed geologic studies of thePacific and Atlantic continental-shelf environ­ments from USGS offices in Menlo Park, Calif.and Wood's Hole, Mass., respectively.

In 1963 Dr. Childs was appointed the 11 thpresident of the Colorado School of Mines.During his seven-year term, the school experi­enced rapid growth, program revision andenrichment, and expansion of industrial andprivate funding.

From 1970 to 1979, Dr. Childs served atTexas Tech University, 4 years as Vice Presi­dent for Research and Special Programs and

5 years as "University Professor," one of onlyfour such appointments. In the former posi­tion, he was responsible for research planningand operations; in the latter, he taught classesin educational administration, museum sci­ences, geology, and geography.

Dr. Childs has been involved in numerouspublic service and professional activities. Hewas a member of the Oil Shale Advisory

Board appointed by the Secretary of theInterior to suggest policy on development ofoil shale as a national resource. He has beena long-standing member of the AmericanAssociation of Petroleum Geologists (AAPG)and was elected president in 1965 and honor­ary member in 1970. He was chairman of theColorado section of the American Institute ofMining and Metallurgical Engineers (AIME).He served 5 years on the Advisory Council ofthe Public Land Law Review Commission.

While at Texas Tech University, Dr. Childswas the special institutional representative tothe New York-based committee for U.S. par­ticipation in the United Nations University. Heserved as the only university representative inthe General Technical Advisory Committeeto the Office of Coal Research. He also servedas chairman of the Energy Projects Councilof the Gulf University Research Consortiumof 14 universities in states surrounding theGulf of Mexico.

In 1979 Dr. Childs was appointed anadjunct professor to the Arizona Bureau ofGeology and Mineral Technology, Universityof Arizona, a position that he still holds today.He assumed the directorship of the MMRRI in1980 and now holds the title of EmeritusDirector. For the last 6 years, Dr. Childs hasdirected a monumental AAPG research project known as Correlations of StratigraphicUnits of North America (COSUNA). Thisproject involved 450 volunteer contributorsfrom all parts of the Nation. Dr. Childs willcontinue to direct the COSUNA project duringhis semiretirement.

,-------------- Fieldnotes ----------~

State of Arizona Governor Bruce BabbittUniversity of Arizona President Henry KofflerBureau of Geology & Mineral Technology

Director :.................. Richard A. SwalinAssociate Director William P. CosartState Geologist & Assistant Director,

Geological Survey Branch Larry D. FellowsAssistant Director,

Mineral Technology Branch J. Brent HiskeyEditor Evelyn M. VandenDolderIllustrators Joe LaVoie. Joy Mehulka

Call for Radiometric Age Determinations in Arizona

The Arizona Bureau of Geology and Mineral Technology hasestablished a computerized database of all K-Ar, Rb-Sr, U-Pb, andfission-track age determinations in Arizona (see "New BureauPublications," this issue). This compilation will be published as aBureau bulletin containing two sections: (1) the compilation; and(2) a series of separately authored, short articles, extended abstracts,and data that report and interpret previously unpublished agedeterminations. All persons with unpublished age determinationsare asked to contact Stephen J. Reynolds at the Bureau.

Vol. 15, No.3 Fall 1985

The Bureau of Geology and Mineral Technology is a division of the University of Arizona.

Arizona Bureau of Geologyand Mineral Technology

845 N. Park Ave.Tucson, AZ 85719TEL: 602/621·7906