The geology and geomorphology of the Buckhead Mesa area, Gila County, Arizona

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Authors Mayer, Larry

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Link to Item http://hdl.handle.net/10150/566597 THE GEOLOGY AND GEOMORPHOLOGY

OF THE BUCKHEAD MESA AREA

GILA COUNTY, ARIZONA

by Larry Mayer

A Thesis Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

19 7 9 STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfill­ ment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknow­ ledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED rvOi 1A

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

W. b . BULL Date * ' Professor of Geology To My Family ACKNOWLEDGMENTS

Partial funding for this study was provided through a grant from the Museum of Northern Arizona. Computer funds were provided by the Geosciences Department, Univer­ sity of Arizona. The typing and reproduction of the manu­ script was funded by NSF grant no. EAR78-03648. The three dimensional perspective plot was produced through PL0T3D, written by D. Nelson, University of Maryland. Isotopic ages cited in this report were made available by the

Laboratory of Isotope Geochemistry, University of Arizona.

The field area was first introduced to me through a course

"Geology of Arizona," taught by P. E. Damon at The Univer­ sity of Arizona. I have benefited from discussions with

P. E. Damon and M. Shafiqullah, Laboratory of Isotope Geo­ chemistry, University of Arizona; H. W. Peirce, Geologist,

Arizona Bureau of Mines and Mineral Technology and C. M.

Menges, graduate student, University of Arizona. Stan B.

Keith provided me with geochemical information and stimu­ lating ideas. The manuscript was improved considerably by the reviews of my thesis committee members, W. B. Bull,

G. H. Davis and E. J. McCullough. I would also like to thank my fellow graduate students who provided an environ­ ment rich in ideas and interest, here at the Geosciences

Department, University of Arizona.

iv TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS...... vii

ABSTRACT ...... x

1. INTRODUCTION ...... 1

Organization of the R e p o r t ...... 4 Previous Studies of Mogollon Rim Development ...... 4 2. GEOL O G Y ...... 7

Precambrian Rocks ...... 7 Older R e m n a n t s ...... 7 Payson Granite ...... 10 Mazatzal Formation ...... 11 Ages of the Precambrian Rocks .... 14 Paleozoic Rocks ...... 20 Cambrian Tapeats Sandstone ...... 20 Devonian Martin Formation ...... 24 Redwall Limestone ...... 29 Naco F o r m a t i o n ...... 30 Cenozoic Rocks ...... 32 F a u l t i n g ...... 36

3. GEOMORPHIC ANALYSIS ...... 45

B a c k g r o u n d ...... 45 A1timetrie Analysis ...... 51 Significance of Topographic Zones .... 52 Drainage Network Modifications ...... 56 Denudation and Network Change ...... 62 Rate of Denudation and Scarp Retreat . . 67 Preliminary Evaluation of Post Miocene Tectonic Activity ...... 71 Conclusions...... 81

4. TECTONIC IMPLICATIONS OF MOGOLLON RIM DEVELOPMENT...... 84

Geophysical Setting ...... 84

v vi

TABLE OF CONTENTS -- Continued

Page

Tectonic Setting ...... 88 Tectonic Interpretations ...... 91

5. SUMMARY QF THE EVOLUTION OF THE MOGOLLON RIM NEAR P I N E ...... 94

APPENDIX: PROGRAM LISTING AND DOCUMENTATION ...... 97

LIST OF REFERENCES...... 104 LIST OF ILLUSTRATIONS

Figure Page

1. Location map of study area showing physiographic provinces and distribution metamorphic core-complexes in Arizona. . . . 3

2. Section of Pine 15-minute topographic map showing location of geologic map and place names used in this report...... 8

3. Small (amplitude 0.7 meter) inclined plunging fold in Sycamore Pendant, view looking east-southeast ...... 9

4. Megacryst of feldspar near contact of Payson Granite and granitic gneiss ...... 12

5. Flow banding at base of Oak Spring rhyolite (bands have been accented in pencil) .... 15

6. Contact between Narrows Quartzite and Oak Spring rhyolite (center of photo), view looking northeast...... 16

7. Ripple marks on thin shale bed in Narrows Quartzite...... 17

8. Flame structures indicating penecontem- poraneous deformation in the Mazatzal Formation...... 21

9. Slickensides along contact between Oak Spring rhyolite and Narrows Quartzite imply slip between beds. 22

10. Clasts of Mazatzal Formation in the Devonian Martin Formation...... 26

11. Basalt intercalated with gravels ...... 34

vii Vlll

LIST OF ILLUSTRATIONS -- Continued

Figure Page

12. Small open fold along Arizona state route 87, north of Diamond Rim fault: view looking we s t ...... 38

13. Stereogram showing orientation relation between fold axis on foot wall, hanging wall and the Diamond Rim fault plane; solid circles are bedding plane orientations . . . 39

14. Frequency histogram of bedding strike orientations ...... 41

15. Geology of Buckhead Mesa ar e a ...... 43

16. Topographic zones of Mogollon Rim Buckhead mesa area plotted on a three dimensional diagram ...... 53

17. Pine Creek drainage network (left) and split-points (right) ...... 58

18. Frequency histograms for split-points on the topographic zones ...... 60

19. Regression equation and line of split-point density as a function of relief ."...... 61

20. Regression equation and line of valley widening as a function of relief ...... 63

21. Possible relationship between denudational demand for sediment (straight line) and a drainage network's split-point adjustments ( c u r v e ) ...... 66

22. Geometric construction used to calculate scarp retreat from denudation rates .... 69 ix

LIST OF ILLUSTRATIONS -- Continued

Page Figure

23. Computer line-printer map showing generalized topography ...... 73

24. Computer generated line-printer slope map. . 74

25. Computer line-printer map showing general geology ...... 75

26. Computer line-printer inventory map showing slopes greater than their mean value on a particular rock type ...... 76

27. Longitudinal profile of Pine Creek channel plotted on semilogarithmic graph; SL values are calculated for each reach along the p r o f i l e ...... 79

28. Sub envelope map of Tucson 2° s h e e t ...... 85

29. Location map showing characteristics of Mid-Tertiary external zone ...... 86

30. Schematic cross sections showing development of Mogollon Rim near Pine ...... 95

31. Control statements used in execution of program COMPOS ...... 100 ABSTRACT

Tectonic geomorphology of the Mogollon Rim near

Pine, Arizona, reveals erosional remnants and topographic zones of morphological dissimilarity that reflect three periods of tectonic base-level fall related to tectonism in the adjacent Basin and Range province. Relative dating of these periods obtained by combining K-Ar isotopic age dates with locally derived functions concerning erosional kinematics indicate the age brackets for tectonic base- level fall are 30-25 m.y. ago, 25-15 m.y. ago and 12 m.y. ago to the present.

The earliest period of base-level fall resulted in a drainage divide separating northeast and south flowing streams. Following formation of this divide, 400 m of south side down displacement along the Diamond Rim fault resulted in a bold escarpment. These tectono- geomorphologic features are believed to express extension that began in the mid-Tertiary. The region of extension is at present characterized by geophysical and topographic transition zones.

The early periods of tectonic base-level fall ended by ca 15 m.y. ago and was followed by pedimentation, scarp retreat and by 12 m.y. ago basalts flowed over both

x pediment and fault. Estimates of denudation rates along the escarpment vary between 50 m and 115 m per million years which imply rates of escarpment retreat that range between 354 m and 857 m per million years. Post 12 m.y. tectonic base-level fall is reflected in canyon cutting into the pediment but is not related to the Diamond Rim fault. CHAPTER 1

INTRODUCTION

The Mogollon Rim in central Arizona is an escarp­ ment, with 450 meters of local relief, which approximates the southern boundary of the Colorado Plateau physio­ graphic province. The Mogollon Rim with its beautiful vistas and geographic coincidence with physiographic- structural transitions, is the kind of landscape feature that inevitably attracts geologists' scrutiny. Despite its geological attraction, geologists have not yet settled questions of the origin and geologic history of the Mogo­ llon Rim.

The goal of this study is to document various con­ straints on the history of the Mogollon Rim, offer a work­ ing hypothesis for its origin assembled from the data presented herein, and attempt to relate such hypotheses to a tectonic framework. In order to reach this goal three categories of information are needed; geologic, geomorphic and geophysical. Geologic control is needed to document the offset of faults that may be related to the Mogollon

Rim and tp evaluate the importance of faulting in Mogo­ llon Rim development. Geomorphic information is needed to

1 2 trace the erosions! development of the escarpment through time. Erosions! surfaces are usually destroyed in the process of denudation but can be preserved where capped by basalts. Basalts serve the dual function of preserv­ ing the erosional surface and providing a minimum age for the surface. Geophysical information can provide evidence for relating the geologic-geomorphic data to regional tectonics.

Of primary concern in organizing this study was finding an area that was both manageable in size and could offer the most potentially useful information. The area selected was Buckhead Mesa which is located (see Fig. 1) between Payson and Pine along Arizona state Route 87.

This mesa is one of several basalt capped mesas that lie in close proximity to the Diamond Rim fault. The basalt capping Buckhead Mesa has preserved gravels and their transport surface. Geophysical data from deep seismic- refraction studies were available for.the area adjacent to

Buckhead Mesa.

The study area falls within the boundary of the

Mountain Region (or Transition Zone) physiographic province and is characterized by rugged terrain. Relief on the

Mogollon Rim is 450 meters, north of Pine. South of Pine,

Pine Creek has excavated a canyon with about 300 meters of 3

Flagstaff

fttfCKSKlM MtS ^ \ 4f HASCUVAt MTS

^ H A tQ U A H A lA MTS

SI IM A tlA M C A

Fig. 1. Location map of study area showing physiographic provinces and distribution of metamorphic core-complexes in Arizona. 4 relief. Access in the study area is generally limited to foot. Vegetation such as manzanita and catclaw limits access in places where it forms dense barriers.

Organization of the Report

This report is divided into five sections. The first and last sections are introductory and summary sec­ tions, respectively. The second section reports on the stratigraphy which is the basis for calculating fault off­

set along the Diamond Rim fault. All units that are cut by the fault, or important in the stratigraphic position of a unit cut by the fault, are described. Section three outlines several geomorphic concepts and techniques useful for analyzing the Mogollon Rim and discusses the resultant data. Section four describes the geophysical character­

istics of the Mogollon Rim and goes on to relate the

geologic-geomorphic data to a regional tectonic setting during the Mogollon Rim development.

Previous Studies of Mogollon Rim Development

Previous workers have suggested the age of the

Mogollon Rim might vary between Paleocene and Pliocene,

an imprecise age bracket of 50 million years. McKee and

McKee (1972) proposed Pliocene uplift of the Colorado

Plateau resulting in drainage reversals (from northeast 5 flowing to south flowing) at that time. Shakel (1975,

1976, 1978) proposed that the Mogollon Rim is the result of migration of a drainage divide or about 80 kilometers of scarp retreat since Laramide time. Peirce, Shafiqullah and Damon (1978) suggest that the Tonto section of the Mogo­ llon Rim is the result of scarp retreat from a pre-12 m.y. old fault. Rowley et al. (1978) indicate that in Utah, structural separation between the Colorado Plateau and

Basin and Range provinces occurred 29 m.y. ago with signif­ icant topographic differences existing by 24 m.y. ago.

Titley (1962) reports that the Diamond Rim fault is ances­ tral to the present Mogollon Rim in central Arizona. Young et al. (1975) show that drainage, along the western edge of the Colorado Plateau in Arizona, was flowing onto the

Plateau from the Basin and Range whose Paleozoic section had been stripped by the end of early Miocene time. Elston

(1978) proposed that regional uplift and faulting occurred between 38(?) and 30 m.y. ago followed by volcanism.

Elston also indicated that erosion led to the full develop­ ment of an escarpment by 15 m.y. ago. Hamblin and Best

(1975) explain that in central Arizona, the Plateau-Basin and Range boundary is a complex erosional scarp developed from Cenozoic regional uplift and is not related to any re­ gional fault system. Hamblin and Best state further that 6 the Basin and Range province developed by inflation, by extension and collapse of the Colorado Plateau; a process that is migrating into the Plateau at a rate of 1cm/year.

Lovejoy (1978) believes the Basin and Range to be a Paleo- cene event. This non-exhaustive account is sufficient to indicate the controversial nature of the Colorado Plateau-

Basin and Range transition. # CHAPTER 2

GEOLOGY

Precambrian Rocks

Older Remnants

Highly altered andesitic basalts interbedded with siliceous wackes and chert crop out over a small area on the west side of Cedar Mesa Canyon (for location see

Fig. 2). Small-scale inclined plunging folds are exposed there, the fold-axes of which plunge west-northwest (see

Fig. 3). This outcrop is here referred to as Sycamore

Pendant.

Scattered outcrops of granitic gneiss" are exposed along the East Verde River in the study area. The gneiss is always found to be surrounded by non-foliated granite.

The foliation of these gneisses strikes west-northwest and dips steeply to the north. Mafic xenoliths sometimes occur in the gneiss. The xenoliths consist of plagio- clase, hornblende and pyroxene. The gneiss is generally of xenoblastic and locally poikioblastic grains of micro- cline surrounding plagioclase(An23 to An^) and hornblende

(Martinsen, 1975, p. 35).

7 Fig. 2. Section of Pine 15-minute topographic map showing location of geologic map and place names used in this report. Fig. 3. Small (amplitude 0.7 meter) inclined plunging fold in Sycamore Pendant, view looking east-southeast. 10

Payson Granite

The predominant exposures along the East Verde

River in the study area consist of pinkish to brownish- pink medium to coarse grained hypidiomorphic granite.

Granite in this area has been described by Lausen and

Wilson (1925) and by Wilson (1939, p. 1129) where it was referred to as the Payson granite. More recently the

Payson granite has been discussed by Martinsen (1975) and Conway (1976). Leon T. Silver has dated the Payson granite by U-Pb method on zircons as 1730 +_ 15 m.y.

(Conway, 1976, p. viii). An undeformed plutonic rock in the same area (Payson granite?) has also been dated, as

1660 + 15 m.y. (Anderson and Silver, 1976, p. 23).

The Payson granite is undeformed. Westward, it grades into a highly contaminated granite and granodio- rite containing abundant mafic xenoliths. In Pine Creek this gradation apparently continues northward where the granite becomes a fine grained granitic rock with abun­ dant mafic inclusions. Wilson (1939, p. 1120) called the rocks in Pine Creek, just south of Natural Bridge, the

Red Rock rhyolite and noted abundant greenstone inclusions.

Below Natural Bridge and in the stream channel north of the Natural Bridge, the rock is clearly a fine grained granitoid. 11

In the East Verde River area, Martinsen (1975, p. 40) refers to the contaminated granite as the Payson

Complex and also noted its gradational relationship with

the Payson granite. The lack of a definite contact and

the granite to rhyolite transition suggests that the

Payson Complex is part of the Payson granite. The Payson

granite clearly cuts the granitic gneiss, which may be a

pendant. Granitic veins cut the gneissic foliation and

locally megacrysts of feldspar occur (see Fig. 4) near the

contact of granite and gneiss.

Mazatzal Formation

The quartzites in the Natural Bridge area were

called Mazatzal quartzite by Wilson (1939, p. 1120) and

correlated with the Mazatzal quartzite of the Mazatzal moun

tains. Conway (1976), working in the Tonto Basin, elevated

the Mazatzal to group status which consisted of quartzites

and slates of the Christopher Mountain quartzite. Mazatzal

rocks are exposed along Pine Creek and its tributaries.

The Mazatzal section consists of a basal conglomerate over-

lain by a quartzite, rhyolite (sill), and finally a thick

sequence of quartzite. These rocks are considered informal \ members of the Mazatzal formation and are named (in ascend­

ing order) Pine Creek conglomerate. Tank Gulch quartzite,

Oak Spring rhyolite and Narrows quartzite member of the

Mazatzal Formation. Fig. 4. Megacryst of feldspar near contact of Payson Granite and granitic gneiss. 13 The Pine Creek conglomerate member is a pebble to cobble and some places boulder conglomerate. The clasts near the contact consist chiefly of moderately rounded to angular fragments of the underlying rhyolite, white quartz and red jasper, in a matrix of subrounded quartz grains and red silt. The red matrix and rhyolite fragments give the conglomerate an overall dusky red appearance. As a rule, the conglomerate lacks bedding, but where the clasts are pebble-sized a crude bedding exists. The thickness of the Pine member appears to vary from 90 m to about ISO m.

This variability may be due to the uncomformable contacts at its base and top. The basal depositional unconformity has also been noted by Wilson (1939).

The Tank Gulch quartzite member overlies the Pine

Creek conglomerate member with slight angular unconformity.

The Tank Gulch is a 30 m to 60 m sequence of poorly sorted conglomeratic quartzite and well sorted quartzite of moder­ ately to well rounded red and white quartz, sand. Locally occurring conglomerate lenses consist of subrounded to angular gravel to cobble sized rhyolite and jasper clasts.

Overall the Tank Gulch is poorly bedded though locally bed­ ding (10-20 cm thick) and graded bedding is well developed.

The Oak Spring rhyolite member overlies the Tank

Gulch with apparent conformity. The rhyolite consists of 14 a basal flow-banded fine-grained rhyolite and grades up­ ward to a spherulitic rhyolite (see Fig. 5). Neither flow-banding nor chilled margin were observed at its upper contact. The rhyolite may be a flow that interrupted Tank

Gulch deposition but is more likely a sill. The Oak Spring rhyolite does not resemble the Red Rock rhyolite in tex­ ture. Thickness of the Oak Spring rhyolite is 22 m near

Natural Bridge.

The Narrows quartzite member conformably overlies the Oak Spring rhyolite (see Fig. 6). The Narrows quartz­ ite crops out on the west, side of Pine Creek, near Natural

Bridge and forms a series of waterfalls called the Narrows southwest of BM5397 where it is extensively exposed. Out­ crops in Oak Spring Canyon are also assigned to this member. The Narrows quartzite is a monotonous sequence of cross-bedded, ripple-marked red to pinkish-gray quartzite and much lesser amounts of purplish-red to purplish-gray

shale. Ripple-marked surfaces are common on the shale beds (see Fig. 7). The total thickness of the Narrows quartzite member is estimated to be at least 900 m.

Ages of the Precambrian Rocks

. The abundant mafic xenoliths in the Payson granite,

the clear cross-cutting relations between the granite and 15

Fig. 5. Flow banding at base of Oak Spring rhyolite (bands have been accented in pencil). 16

Fig. 6. Contact between Narrows Quartzite and Oak Spring rhyolite (center of photo), view looking northeast. Fig. 7. Ripple marks on thin shale bed in Narrows Quartzite. 18 gneiss, and the parallel structural trends of the gneiss and Sycamore pendant suggests the Sycamore pendant and gneiss were the host rocks into which the Payson granite intruded. Martinsen (1975) believed the granite, where it contained abundant mafic inclusions, was a distinctly older pluton which was itself intruded by more typical

Payson granite. The granite to rhyolite gradation, that includes Payson Complex (Martinsen 1975), does not tend to support subdividing the plutons. The rhyolite in Pine

Creek, called Red Rock rhyolite by Wilson (1939) appears to be contemporaneous with the Payson granite and it too contains numerous inclusions. This gradational relation­ ship may be similar to the Tonto Basin. Gastil (1958) reported that the granites in Tonto were overlain by their own mantle of rhyolite.

The Mazatzal Formation, as evidenced by clasts of

Red Rock rhyolite within the Pine Creek member, is dis­ tinctly younger than the rhyolite-granite assemblage.

Conway (1976) describes the relationships in the Tonto

Basin as indicating that the Payson granite is intrusive to the Mazatzal rocks. Field evidence in this study sug­ gests that the Payson granite was basement to the Mazatzal; this agrees with the original observations of Wilson (1939). The absolute ages of these Precambrian rocks is somewhat problematic. Both younger (1660 +_ 15 m.y., 19

Anderson and Silver, 1976, p . 23) and older (1730 + 15 m.y., Conway, 1976, p. viii) ages have been obtained from the granite. The age of the rhyolite is 1715 m.y.

(Anderson and Silver, 1976, p. 23) and appears to be the most reliable. The gradational relation between the gran­ ite and rhyolite suggests that an intermediate age for the

Payson granite is likely, perhaps 1715-1700 m.y.

The Sycamore pendant and the gneiss are older than the Payson granite. The relationship of the Sycamore pen­ dant and gneiss may be analogous to the relationship between the Green Gulch volcanics and the Government Can­ yon granodiorite in the Prescott and Paulden quadrangles.

The Government Canyon, which intrudes the Green Gulch, has been dated as 1760 + 15 m.y. and shows a distinct folia­

tion. The ages of volcanics that are older than the

Government Canyon is 1775 j;10 m.y. (Spud Mountain Vol­

canics, Anderson and Silver, 1976, p. 19). The Sycamore

pendant and gneiss may be part of this older volcanic

terrain in which case their age would be about 1760 m.y.

A distinctly younger volcanic terrain exists to the

southeast to which the Sycamore may belong, whence the age

of the Sycamore-gneiss complex may be 1730 m.y.

The Mazatzal Formation must be younger than the

1715-1700 rhyolite-granite assemblage and older than the

overlying Paleozoic rocks. The maximum possible span of 20 the unconformity is about 1000 m.y. There is some evidence that penecontemporaneous deformation took place in the -

Mazatzal•(see Fig. 8) though subsequently the Mazatzal was folded', obstensibly by flexural slip style (see Fig. 9).

Paleozoic Rocks

Cambrian Tapeats Sandstone

Nomenclature. Noble (1914, 1922) proposed the name Tapeats sandstone for basal Tonto group rocks in the

Grand Canyon area. Ransome (1916, p. 160) described the basal Paleozoic sandstone in the Pine area as Tapeats (?) based on lithology. Stoyanow (1942, p. 1267) and Huddle and Dobrovolny (1952, P. 79) regarded the basal sandstone

in the Pine Creek area as basal Devonian as did Teichert

(1965, p. 45). The basal Paleozoic sandstone along the

East Verde River was considered to be Tapeats by Huddle

and Dobrovolny (1952) and to be basal Devonian by Teichert

(1965, p. 23). Lithology. The Tapeats sandstone is a reddish-

brown to brown cliff-forming unit that consists of a basal

conglomerate and an overlying cross-bedded sandstone. The

basal conglomerate, which is locally absent, is composed

of subrounded quartz and feldspar fragments with scat­

tered pebbles and cobbles of quartz and locally quartzite. 21

Fig. 8. Flame structures indicating penecontemporaneous deformation in the Mazatzal formation. Fig. 9. Slickensides along contact between Oak Spring rhyolite and Narrows quartzite imply slip between beds. 23

The sandstone unit consists of very fine-to coarse-grained quartz sand and feldspar with variable amounts of silt.

Bedding in the sandstone varies from 8 cm to 100 cm in thickness. Cross-bedding dip directions indicate a west- southwest transport direction (Martinsen, 1975, p. 60).

Thickness and Stratigraphic Relations. Martinsen

(1975, p. 58) reported a thickness of 15 m to 20 m in the

East Verde River area. Thickness of the Tapeats varies

from 15 m in the East Verde River area to 3 . 6 m near Nat­ ural Bridge where it pinches out on the Mazatzal Formation.

The Tapeats thickens to the north in the Grand Canyon area where it is 30 m to 91 m thick (McKee, 1974, p. 46). The

lower contact is unconformable with older Precambrian rocks

and relief on this surface is less than 2-3 m.

Age and Correlation. The basal Paleozoic conglom­

erate and sandstone in the East Verde River area is cor­

related with the Tapeats sandstone of Huddle and Dobrovol- ny (1952) rather than the Beckers Butte member of the

Devonian Martin Formation (Teichert, 1965, p. 23). This

correlation is supported by the cross-bedded character

and transport direction of the sandstone and by paleomag-

netic evidence which indicates a temporal equivalence

with the Tapeats of the Grand Canyon (Elston and Bressler,

1978, p. 104). The basal Paleozoic conglomerate in the 24

Natural Bridge-Pine Creek area is tentatively correlated with the Tapeats of Ransome (1916). Although Teichert's

(1965, p. 152) section at Natural Bridge seems to support

his assignment of the basal Paleozoic strata to the Martin

Formation, my traverses to the south of Teichert’s show

a sequence of conglomerate-arkosic sandstone that is

overlain by conglomeratic-sandstone. The conglomeratic-

sandstone contains cobbles of the Mazatzal Formation but

is otherwise well sorted. The basal conglomerate-sand­

stone sequence is more similar to typical lithologies in

the Tapeats. In this case the Tapeats apparently pinches

out on the Mazatzal and rhyolite near Natural Bridge.

Devonian Martin Formation

Nomenclature. The name Martin Limestone was pro­

posed by Ransome (1904, p. 33) for Devonian limestones in

southeastern Arizona. Stoyanow (1936) named the Devonian

limestones at Jerome the Jerome Formation because he con­

sidered it to be distinct and separated by the "Mazatzal

Land" barrier from the southeastern part of the state.

Huddle and Dobrovolny (1952, p. 73) considered these same

Devonian rocks to be a continuous mappable unit and pro­

posed the name Martin Formation (rather than limestone)

because of the large percentage of.sandstone and shale

present in their section. Krieger (1965) used the term 25

Martin Limestone in the Jerome area. Teichert (after

Martinsen, 1975, p. 65) recommended raising the Martin

Formation to group status and subdividing it into the

Beckers Butte and Jerome Formations. Martinsen (1975) used the Martin Group nomenclature to describe the Devon­ ian section along the East Verde river. This report conforms to the Martin Formation nomenclature. The

Jerome nomenclature has been somewhat confused, being used differently by Stoyanow and Teichert and by Teichert*s

(1965) inclusion of the Cambrian Tapeats in his basal

Devonian Beckers Butte member near the East Verde river.

Lithology. The lithologies within the Martin For­ mation range from sandstone, siltstone, mudstone, to pure limestone and dolomite. The basal section along

Pine Creek consists of about 6 m of a slope forming con­ glomerate containing dark gray to black angular limestone fragments up to 20 cm long. The source of these clasts is not known. Overlying the conglomerate is a 2-3 m thick cliff-forming gray sandstone, which consists of well- rounded fine-grained quartz sand. Locally, exposures along

Pine Creek show pebbles and cobbles of the Mazatzal

Formation in this unit (see Fig. 10). Closer to the East

Verde river, the sandstone unit becomes coarser, contains more feldspar, and lacks the Mazatzal clasts. Above this 26 27 unit is about 8 m of poorly exposed light gray aphanitic dolomite and limestone that weathers dark gray. This unit grades upwards into a sandy dolomite alternating with reddish-brown (weathered) massive dolomite beds (0.8 m thick). Up the section the limestones give way to a predominantly clastic section consisting of gray fine­ grained sandstones overlain by a 2 m thick shale sequence with thinly interbedded limestone. Sandstones in this sequence vary from very fine-grained to medium-grained and are slightly arkosic. The clastic sequence grades through a 6 m thick sequence of very friable calcareous mudstones and shales into gray crystalline limestone interbedded with shale. This limestone contains abundant brachiopods

(Atrypa) and coral (Pachyphyllum) debris locally. These fossils are commonly silicified.

Thickness and Stratigraphic Relations." The thick­ ness of the Martin Formation in the study area varies from pinch-out on the Mazatzal Formation to 100 m and generally ranges between 62 m to 100 m. Huddle and Dobrovolny (1952) measured the Martin Formation near the East Verde river-

Highway 87 intersection as about 112 m. Martinsen (1975) reports a thickness of about 125 m. Peirce (after Martin-

sen, 1975) reports a thickness of 148 m. The Martin For­ mation rests with angular unconformity on Precambrian and Cambrian rocks (Huddle and Dobrovolny, 1952), and is un- conformably overlain by the Redwall limestone.

Age and Correlation. The basal conglomerate and sandstone (total thickness of 9 m) is correlated with

Teichert's (1965) type Beckers Butte member of the Martin

Formation but not with his Beckers Butte member near the

East Verde river. Field correlation is made on the basis of lithology. Paleomagnetic data (Elston and Bressler,

1978) confirm the distinction of the Tapeats and Beckers

Butte in the East Verde river area and demonstrate that the Beckers Butte to be Devonian (late Givetian or early

Frasnian) and temporally correlated with the Temple Butte limestone of the Grand Canyon. The conglomerate and sand stone is also correlated with Huddle and Dobrovolny*s

(1952) basal lower member of the Martin Formation. The remaining section of Martin Formation is correlated with the Jerome member of the Martin Formation. The paleo­ magnetic data of Elston and Bressler (1978) also support this correlation.

The basal Paleozoic conglomerate and sandstone in Pine Canyon was considered Tapeats (?) by Ransome

(1916) and basal Devonian by later.workers (Huddle and

Dobrovolny, 1952, p. 59). Based on lithology and stratigraphic relations (as discussed above) it is here placed in the Cambrian Tapeats. 29

Redwall Limestone

Nomenclature. Gilbert (1875, p. 162) originally proposed the name Redwall limestone and Noble (1922, p. 22) restricted the usage to include only Mississippian strata. Gutschick (1943, p. 1-11) divided the Redwall into four members as did Krieger (1965, p. 60-61).

Lithology. The Redwall limestone in the study area dominantly consists of a solution or rubble breccia.

The solution breccia is made up of solution rounded yellowish-green to greenish-gray crystalline limestone blocks that vary in size from 5 cm to 80 cm. Surrounding these blocks is a red silt that forms a matrix and stains the limestone blocks red. The solution breccia can be seen to grade laterally into a massive limestone.

Thickness and Stratigraphic Relations. Region­ ally, the Redwall limestone varies in thickness from

150 m in the Grand Canyon area (McNair, 1951, p. 515),

80 m in north-central Arizona (Gutschick, 1943, p. 4), to 65 m in the Paulden quadrangle (Krieger, 1965 p. 60).

Huddle and Dobrovolny (1952, p. 104) report 20 m of

Redwall near the East Verde river north of Payson.

Martinsen (1975, p. 81) reports between 25 m and 62 m of

Redwall in the Same vicinity. Observed thickness of the

Redwall was generally about 36 m. Variable thicknesses are due to unconformable upper and lower contacts. Karst 30 conditions are thought to be responsible for the exten­ sive solution of the Redwall (Huddle and D obrovolny, 1952,• p. 88) and infilling of caves by the overlying Naco For­ mation makes this contact irregular.

Age and Correlation. The solution breccia and crystalline limestone is correlated with the Redwall units described by Krieger (1965, p. 60-61) and Huddle and

Dobrovolny (1952, p. 86-90) based on similar lithology and

stratigraphic position. The age of the Redwall is con­

sidered Kinderhookian and Osagean (Krieger, 1965, p. 61).

Naco Formation

Nomenclature. The name Naco Limestone was origi­

nally applied to upper Pennsylvanian and Permian strata

at Bisbee by Ransome (1904), and later raised to group

status by Gilluly, Cooper and Williams (1954). Huddle

and Dobrovolny (1952) used the name Naco Formation to de-• scribe time equivalent rocks in central Arizona. The Naco

Formation nomenclature has been followed in central Arizona

by Kottlowski and Havener (1962) and Brew (1965). Brew

(1965, p. 34) divided the Naco Formation into three infor­

mal members; (in ascending order) the Alpha, Beta and

Gamma members. Martinsen (1975, p. 83) followed Brew's

nomenclature in the East Verde river area north of Payson. 31

Lithology. The basal unit of the Naco Formation is a massive chert pebble conglomerate. The conglomerate lacks bedding and consists of angular to sub-rounded chert fragments in a fine sand matrix. Locally the m a ­ trix is entirely a red silt in which case the unit is poorly consolidated. West of Buckhead Mesa this unit is absent or not exposed. Excellent outcrops occur along

Highway 87 north of the East Verde river and along a dirt road to Cedar Mesa. The chert conglomerate is thought to represent a residual soil formed on the Redwall Limestone

(Huddle and Dobrovolny, 1952, p. 89), and may therefore be the thickest in sinkholes formed in the Redwall. Lim­ ited exposures do not permit positive proof that the extent of the chert conglomerate is more or less uniform­ ly distributed. Huddle and Dobrovolny (1952 , p. 89) suggest these conglomerates occur generally as pocket fills.

Overlying the chert conglomerate is an apparently structureless red sandy siltstone which grades upwards to a sequence of fissile calcareous mudstones and gray shales alternating with 3 cm to 5 cm thick white to buff crystal­ line limestones. The uppermost sequence consists of very fine-grained reddish-gray sandstone alternating with cal­ careous siltstones, sandy siltstones and medium-grained gray to pinkish-gray sandstones. 32

Thickness and Stratigraphic Relations. Brew (1965, p . 122) measured about 130 m of Naco rocks near the East

Verde river. Martinsen (1975, p. 84) reports thicknesses of the Naco varying between 25 m and 130 m in the East

Verde area north of Payson. Estimated thicknesses for this study varied between 40 m near the East Verde to

137 m north of the control road. Huddle and Dobrovolny

(1952, p. 90) report a thickening of the chert residium towards Mazatzal Land, though Brew (1965) found no such thickening.

Age and Correlation. The basal chert conglomerate

is correlated with the basal chert residium of Huddle and

Dobrovolny (1952) on the basis of lithology and strati­ graphic position above the solution brecciated Redwall

Limestone, and with the basal unit of Brew’s (1965) Alpha member. The overlying sequences may be correlated with

Brew's Beta and Gamma members. The age of the Naco

interval is probably Demoinsian (Kottlowski and Havener,

1962) and possibly younger (Brew, 1965).

Cenozoic Rocks

Cenozoic rocks in the Buckhead Mesa Area consist

of olivine-basalt flows and the underlying gravel to cob­

ble conglomerate. The conglomerate is poorly sorted and

massive though cobble imbrication structures give the impression of a crude bedding. The gravel and cobbles

are well-rounded to angular but are predominantly sub-

angular to sub-rounded. The matrix consists of sand and

silt and is calcareous in places. Lithologies repre­

sented by the cobbles include (in order of descending

abundance) quartzite, sandstone, siltstone, limestone,

conglomerate, and minor amounts of granite, diorite,

chloritized basalt and silicified fossil debris. These

lithologies appear to be present locally, but K-Ar dating

may suggest a source to the south (Peirce, oral communi­

cation, 1978) .

Dip directions on imbricate cobbles indicate that

transport was from north-northwest to south-southeast at

• Buckhead Mesa and northwest to southeast along Highway 87.

The conglomerate unconformably overlies the Naco

Formation or older Paleozoic rocks. The conglomerate,

referred to as the Buckhead Mesa gravels, is in turn over-

lain conformably by basalt flows. Locally the basalt is

intercalated with the Buckhead Mesa gravels (see Fig. 11).

The basalts are generally massive at their base

and become vessicular towards the top. The total maximum

thickness of the basalt-conglomerate sequence is estimated

to be 40 m, while 30 m is most common. The basalt capping

Buckhead Mesa has been dated by the K-Ar method as Fig. 11. Basalt intercalated with gravels. 35 12.1 + 0.40 m.y. and has a K content of 0.49 percent

(Shafiqullah, oral communication, 1978).

A travertine deposit occurs along Pine Creek and forms the Tonto Natural Bridge. The deposit, con­ sisting of travertine and chara, forms a 40 m high bridge over Pine Creek. Its origin is enigmatic. Springs issuing into Pine Creek adjacent and by way of the Nat­ ural Bridge are high in carbonate content. Since debris found near these springs, such as pop bottles, have been totally engulfed in a 1 to 2 mm carbonate crust, carbon­ ate precipitation must be rapid. The base of Natural

Bridge is large boulders up to 2 m in diameter that have been engulfed in carbonate. The top of the Bridge has a laminar carbonate zone. Lichens, examined on the adjacent valley walls, show that the talus accumulating on the

Natural Bridge is younger than the adjacent valley walls.

Lichen diameters on the talus blocks vary between 3-6 cm whereas on the valley walls lichen diameters vary between

8-11 cm. Using the pop bottle crust as a measure of pre­

cipitation (0.001 m/10 yrs.) , it would take 400,000 years

for 40 m to accumulate. However, since up to 80% of the

Bridge may have been boulders, the time necessary to build

this size travertine deposit reduces to 80,000 years. 36

Faulting

Is the Mogollon Rim near Pine purely an erosion- al feature unrelated to faulting, is it the result of regional faulting parallel to the present Mogollon Rim or is it the result of some unknown combination of faulting and erosion? In order to address these questions, documentation of the age and magnitude of faulting, pos­ sibly related to the Mogollon Rim, is needed.

The major fault in the study area is the westward extension of the Diamond Rim fault (Titley, 1962). Titley reports 300 m of southside down, normal displacement on the steeply dipping Diamond Rim fault north of Payson, which is east of Buckhead Mesa. Titley also notes that the fault has increasing displacement westward, towards

Buckhead Mesa.

In the Buckhead Mesa area, the Diamond Rim fault cuts the Precambrian Mazatzal Formation, the Sycamore

Pendant and the Tapeats Sandstone through Naco Formation sequence. Based on topographic elevation differences between Cedar Mesa and Buckhead Mesa, its reasonable to conjecture that the Tertiary gravels-basalt sequence is also slightly displaced by the fault (perhaps 50 m).

The fault is not well exposed in the study area. Location 37 of the fault is based on the truncation of the Paleozoic rocks against Mazatzal Formation on the northwest side of

Buckhead Mesa. This section of the fault is also mapped on the Gila County geologic map (Wilson, Moore and Peirce,

1959).

Initially, I had attempted to determine the post-

Paleozoic displacement by projecting the Naco-Redwall contact to the fault, on the northwest side of Buckhead

Mesa, and calculating the elevation difference between the projected elevation of the contact and the elevation of the contact on the upthrown side. The displacement thus

calculated is about 250 m. I have chosen not to use this

figure for two reasons: the Naco-Redwall contact is not well exposed at that locality; structural complications

due to folding may affect the calculation of displacement

at that locality.

Open folds of variable amplitude trending

east-northeast, may be seen along Arizona route 87 both

south and north of the fault within the Paleozoic

formations. An example of such an open fold is shown in

Figure 12. A second possible folding complication is

drag folds. Conceivably, either form of folding could

change the value for fault displacement. Orientation

data were collected south of the fault, along the west

side of Buckhead Mesa (see Fig. 13). Cursory inspection . Fig. 12. Small open fold along Arizona state w route 87, north of Diamond Rim fault; view looking west. oo 39

f o l d l im b s FROM HISTOGRAM

AXIAL SURFACE (FOOT WALL)

AXIAL SURFACE (HANG ING WALL) FAULT PLANE

FOLD LIM B S FROM SMALL FOLD

Fig. 13. Stereogram showing orientation relation between fold axis on foot wall, hanging wall and the Diamond Rim fault plane; solid circles are bedding plane orientations. 40 of Figure 13 implies that the beds were not folded; rather they were dipping gently to the northeast.

In order to resolve possible measurement error inherent in recording shallow dips the bedding attitude orientations were plotted on an orientation histogram with a slight modification. The azimuths were plotted as azimuth certainty bands. The certainty band for each attitude was determined by dividing 90 degrees by the dip of each measurement. A measurement that had a dip of one degree would be plotted with 90 degree bands. A measure­ ment with a dip of 11 degrees would have an 8 degree band, etc. The resulting histogram (see Fig. 14) was interpreted as a bimodal distribution. The mean azimuth and mean dip of the distributions were plotted on a stereonet (see

Fig. 13) along with the limb orientations of the fold

shown in Figure 12 (from upthrown side of fault). The

orientations of the respective axial surfaces are

subparallel to the fault plane, suggesting a connection

between fault and folding; perhaps drag folding.

To avoid complications near the fault, I decided

to calculate the displacement on the fault by pro­

jecting the basal contact of the Tapeats Sandstone on

the southern side of Buckhead Mesa into the fault, and i. 14. Fig.

FREQUENCY Frequency histogram of bedding bedding of histogram Frequency tie orientations. strike AZIMUTH 42 computing the difference in elevation of the projected contact and the basal Tapeats on the upthrown block. The dip of the Tapeats, used in the calculation, was 3 degrees.

This method shows the post-Paleozoic displacement of the

Diamond Rim fault to be about 400 m (see Fig. 15a,b).

In subsequent discussion of the relation of the

Diamond Rim fault to the Mogollon Rim, I have made several

simplifying assumptions which need to be explicitly stated

at this time. Originally I noted that the Mogollon Rim

could be the result of erosion or faulting or a combina­

tion of the two. This relation can be stated: MR * F + E (1) where, MR stands for the relief on the Mogollon Rim, F is

the relief caused by faulting and E is the relief caused

by erosion. I assume that the set F , contains only one

element, that is the Diamond Rim fault's displacement.

This assumption results in the conclusion that whatever

the impact of faulting on creating the Mogollon Rim was

it will be a minimum estimate, since it is conceivable

that other faults, yet unmapped, may contribute to the

total relief represented by the Mogollon Rim. The set E

is equal to the relief that is not F or symbolically, F.

Thus the estimate of erosional influence on the Mogollon

Rim is a maximum one, because it is possible that non-

Diamond Rim faulting is included in set E . explanation ARY R IA T R E T Y R A N R E T A U Q N A I N A V L Y S N N E P ARY R IA T R E T SSI S N A I P P SSI I S IS M N A I N O V E D

“□□□□□□□□□a N A I R B M A C AN IA R B M A C E R P T L A S A B M U I V U L L A GRAVELS D A E H K C U B ON IO T A M R O F O C A N TE IT N A R G N O S Y A P L A Z T A Z A M E N O T S D N A S TAPEATS ON IO T A M R O F N I T R A M E LIMESTONE L L A W RED T N A D N E P E R O M A C Y S i. 5 Gooyo ukedMs area Mesa Buckhead of Geology 15.Fig. km 2 . elgc rs scin across section cross Geologic b. . elgcmp n oain of location and map Geologic a. placement across the Diamond Rim Diamond the across placement rs scin lutaig dis­ illustrating section cross fault. h Daod i fault. Rim Diamond the 44 The total relief on the Mogollon Rim, from escarp­ ment to the Diamond Rim fault, is about 600 m. It is possible that 400 m of this relief is related to faulting.

Thus one may infer that 200 m of relief is related to

erosion. However these inferences demand another assump­

tion. One must assume that the total 400 m of displace­ ment on the Diamond Rim fault occurred during Mogollon

Rim formation rather than say, 100 m in Triassic time,

100 m in Jurassic time and 100 m in Cretaceous time, thus

leaving only 100 m displacement to "occur in th Cenozoic.

Indeed, if it was possible to demonstrate that the fault­

ing was largely pre-Cenozoic, one would come to the con­

clusion that the Mogollon Rim was largely an erosional

feature.

The purpose in making the above assumptions is

that it allows further data to be collected within a

logical framework. The data that needs to be included

in the next stage of analysis is geomorphic data. CHAPTER 3

GEOMORPHIC ANALYSIS

Background

Tectonic geomorphology is here defined as the de­ lineation and study of landforms that have been modified or resulted from crustal movements and includes the study of geomorphic processes that have been affected or initia­ ted by tectonism. A problem implicit in tectonic geomor­ phology is how does one determine whether a landform has been modified by tectonism or whether the landform is merely the result of non-tectonic geomorphic processes.

To understand the approach used in this paper to problems in tectonic geomorphology one must also understand some basic concepts in geomorphology.

In a practical sense, tectonic geomorphology is

like exploration geophysics. Geophysical methods such as

seismic refraction and electrical resistivity surveys sup­ ply an energy source whose characteristics like wave ve­

locity serve to determine boundaries between different

rock (materials) properties (such as density). Similarly

tectonic geomorphology seeks to interpret the relations

between surface energy in the form of streams, runoff.

* 45 46 etc. and surface material by way of resulting land- forms. Basic to interpreting geomorphic data is some knowledge of how energy and landforms are related.

A fundamental fluvial-process concept is base-level adjustment and entropy. Base-level is a datum below which streams, at a specific time, can do no work. Physically, this datum may be represented by features such as strath terraces, pediment terraces, etc. Entropy in a fluvial system refers to a tendency for achieving a least-work/max- imum probability energy grade (Shannon and Weaver, 1949;

Pelto, 1954; Miller and Kahn, 1962; Leopold and Langbein,

1962; Thornes and Brunsden, 1977) and this is reflected in channel hydraulic geometry and basin geometry. In probab­ ilistic terms (Miller and Kahn, 1962, p. 462; Thornes and

Brunsden, 1977, p. 172) entropy has been expressed by equation 2:

S = -K Epi In pi (2) where S is entropy. Entropy is maximized when the prob­ ability (p) of each state is equal and minimized when only one state is possible and the others have a zero prob­ ability. The constant K is Boltzmann's gas constant. At absolute base-level only one possible state exists and S

is therefore zero, the point at which no work is done.

A consequence of streams' tendency towards maxi­ mizing entropy is that theoretically streams should have a 47 characteristic longitudinal profile approximating an expo­ nential function which when plotted on a semi-logarithmic graph is a straight line. The longitudinal profile however is only one of a host of possible adjustments between hy- ’ draulic variables. Deviations from the theoretical profile may physically represent geologic constraints such as vari­ ability in the channel material to erosion, climatic con­ straints which affect the quantity and calibre of load or base-level perturbations such as faulting and alteration of channel elevations.

In response to one of the above constraints streams can adjust internally and externally. Internal changes include velocity gradients and eddy currents, transient bed forms and fluctuations of the hydraulic variables:

Width, w = zQf Depth*, d = cQ* Velocity, v = KQ within the confines of a channel. External adjustments are modifications of the boundary conditions of the flow and include channel slope and alterations of the physical chan­ nel boundaries.

Studying a constraint that may have occurred long ago requires selection of a variable which can retain or remember the record of a long past perturbation. Internal 48 adjustments do not appear to fit this criterion. In head­ water or erosional environments, channel slope seems to be a suitable variable with which to assess perturbations along a channel, especially where canyons limit the phys­ ical changes in channel width. The concept of a theoret­ ical longitudinal profile is a useful tool that can be used to compare the actual channel with an "unconstrained model" (Leopold and Langbein, 1962) and thus delineate where constraints are reflected in channel slopes.

The morphologies of landform elements such as hillslopes, longitudinal profiles of channels, mountain fronts, scarps, alluvial fans, etc. provide data which when quantified in some manner, can be useful in evalu­ ating the effect of base-level change. Bull and McFadden

(1977) use quantitative morphologic parameters such as mountain front sinuosity, valley width, basin elongation in conjunction with qualitative parameters like fan mor­ phology, to categorize vertical tectonic activity along mountain fronts bounded by depositional basins. Hack

(1975) uses a quantitative index of channel slope, de­

fined by equation 3:

H1~H2 InL^-TnL^

where SL is the slope index. H^, are elevations at two 49 points along the channel floor and are the dis­ tances of these two points from the channel's headwaters.

Hack states that SL values are related to stream compe­ tence. Higher SL values reflect increased competence.

Hillslope profiles are in some way related to base- level of the adjacent channel. Bull (1975) has shown that hillslope ridge-crests may be more convex .in areas of base- level fall. Meyer.and Kramer (1969) through laboratory models show that concave-upward hillslope forms are the most stable. General hillslope form can be considered a function of colluvial transport rates versus rate of fluvial downcut­ ting. Vector diagrams can be used to illustrate this relationship, and reaffirm the deterministic nature of channel-hillslope relationships.

Rock type is an important variable in hillslope morphology, weathering rates and size of weathered materi­ al affect the rate at which material will be made avail­

able for transport by colluvial processes. All else being constant (e.g.,'base-level control, climate, distance

from channel to hillslope divide, etc.), rock-types that

supply their weathering products at relatively slower rates

will have steeper slopes in an erosional environment.

Similarly, a lowering of base-level will increase the

side-slope steepness by increasing the stream vector,

which may account for some convex profiles. General shear 50 stresses on hillslopes are described elsewhere (Carson,

1971). The concept utilized here is that hillslopes tend to geometrically adjust to distribute stress along the slope so as to minimize strain (i.e. transport of material). This concept is in accordance with the experi­ mental results of Meyer and Kramer (1969). Different lithologies* weathering products affect the shear stress necessary for its transport. Rock type therefore is a variable within boundary conditions that affect hillslope declivity.

Several cartographic techniques in topographic analysis exist which aid interpreting landscapes in tec­ tonic geomorphology. One such technique is called the subenvelope map. Subenvelope maps are isopleth maps of

stream channel elevation that generalize topography.

Subenvelope maps differ from other generalized topographic maps in that they use the drainage network and their chan­ nel elevations for sample points rather than regular grid

sampling. Subenvelope maps have been used to postulate

future topographic surfaces (Stearns, 1967), to show the

present generalized topography (Hack, 1973) and to delin­

eate linear features (Mayer, Prowell and Reinhardt, 1977).

Subenvelope maps are not topographic maps and the contours

generally lie below the actual topographic surface. 51

Subenvelope map contours and topographic contours coincide only in the contoured stream channels.

In order to interpret subenvelope maps one can con­ sider the isopleths to represent base-level contours.

Abrupt steepening of the contours show steepening of stream channels gradient and if regional in extent, they are seen as linear features on the subenvelope map. Local steep­ ening of stream channel gradient may be due to geologic constraints but regional steepening is more likely to be tectonic in origin.

More general methods of cartographic topographic analysis have been discussed by King (1966, p. 231-272) and include areal analysis, profiling, altimetric analy­ sis and block diagrams. In a general sense, altimetric analysis consists of sampling elevation from a contour map and describing'the resultant frequency distributions.

Altimetric analysis is often helpful in describing ero- sional surfaces.

Altimetric Analysis Altimetric analysis (King, 1966) of the area is based on study of U.S. Geological Survey 1:24000 and

1:62500 scale topographic maps and airphoto interpretation.

The topography was digitized by overlaying a grid on the

1:62500 scale Pine quadrangle and sampling every 250 in, 52 resulting in a matrix of 3600 elevations. The elevation matrix was punched on computer cards and processed in order to obtain a histogram of frequencies and basic sta­ tistics. The frequency analysis shows that four distinct topographic zones exist. These zones are called, in order of descending elevation, 1, 1-t, 2, 2-t, where "t" sig­ nifies base-level transition.

Zone 1 is an erosional surface, cut on Coconimo sandstone or Supai rocks, that decreases in elevation to the South. Zone 2 is a transport surface upon which the

Buckhead Mesa gravels and basalts lie, and also decreases in elevation southward. Zones 1-t and 2-t are steep- sloped transitional zones (see Fig. 16).

Significance of Topographic Zones

Zone 1 represents an initial reversal of drainage from northeast flowing to south flowing. The Rim gravels

(Price, 1950) of Eocene-Oligocene age represent a time of northeast flowing drainage from the Mogollon Highlands to the Plateau (Cooley and Davidson, 1963). Zone 1 which has been cut onto Supai rocks on Milk Ranch Point (Shafiqullah, oral communication) reflects the establishment of a drain­ age divide on the Plateau that separated north flowing from south flowing drainage systems, at least locally.

The age of this early divide is bracketed by the Eocene 53

ZONE / - /

MILK RANCH POINT ZONE Z / ZONE /

MOGOLLON • RIM

BUCKHEAO PINE MESA CREEK ZONE 2 E. VERDE RIVER ZONE 2‘ t RTE.87

KILOMETERS

Fig. '1 6 . Topographic zones of Mogollon Rim Buckhead Mesa area plotted on a three dimensional diagram. 54

Oligocene Rim gravels and by volcanics from Baker Butte which flowed down this surface. The oldest basalt from

Baker Butte is dated at 14 m.y. by K-Ar (Shafiqullah, oral

communication, 1978). Denudation of .significant magnitude

separates zone 1 and zone 2 and must have required a large

time period. Using the Anhert equation (Anhert, 1970)

implies that 10 m.y. (denudation at 3 cm/1000 years) would

be needed to account for differences in elevation of zone

1 and zone 2. Establishment of the initial drainage

divide likely occurred about 25 m.y. ago. One may specu­

late that modern analog for what the Rim north of Pine

looked like 25 m.y. ago may be found in the. area of

Carrizo Creek or east of Carrizo Creek. In that area, which

lies east of the Canyon Creek fault (Finnell, 1962), the

Mogollon Rim is a much more subdued feature.

Zone 2 was a transport surface upon which gravels

of local derivation were being moved from northwest to

southeast. Zone 2 includes Buckhead Mesa, Black Mesa, and

extends north towards Pine which is built on this surface.

Clearly, zone 2 must already have existed when basalts cov­

ered parts of it 12 m.y. ago. This surface, which extends

into the Rim as an embayment, means that the Mogollon Rim

north of Pine must have existed 12 m.y. ago. Those workers

(Peirce et al., 1978) who use the age date of the Buckhead

Mesa basalt to estimate Rim retreat as 1 kilometer per 55 million years for the last 12 million years are therefore calculating an upper bracket or a maximum possible value for retreat. Zone 2 may indicate that pedimentation pro­ cesses were operating 12 m.y. ago on the already existing escarpment and the rate of base-level fall had waned.

Zone 1-t represents a transitional zone indicating that a rapid fall in base^level occurred between 25 m.y. ago and 12 m.y. ago. Pine Creek was possibly flowing into a basin-type structure that was developing between the

Mazatzal Mountains and the Sierra Anchas; thus Pine Creek was tributary to the Tonto drainage system. This con­ clusion supports the work of Pederson and Royse (1970) who believed the East Verde river to have been part of the Tonto Drainage system in Miocene time.

Zone 2-t represents a transitional zone indicating base-level fall post-dating the 12 m.y. zone 2. This zone may be related to Verde Valley faulting which subsequently resulted in the beheading of part of the Tonto drainage system by the modern East Verde river. The canyon cutting of Pine Creek is for the most part due to the lower base- level control exerted by the East Verde river, and possi­ ble faulting between Buckhead Mesa and the East Verde river. Drainage Network Modifications

A drainage network is the spatial expression of stream systems' distribution of work (or “network"). Many workers have established the concept that a network repre­ sents a most probable state or a state of least work

(Leopold and Langbein, 1962 ; Shreve, 1967; Woldenberg,

1968; Jarvis, 1977). Branching within networks have been

studied (Woldenberg, 1966; Howard, 1971a,b; Dacey and

Krumbein, 1976) but without yielding information readily usable for field study (Unwin, 1977).

The ability to delineate and document four zones within the Pine Creek catchment offers an opportunity to

examine network change that may have occurred on zones

1-t and 2-t. These zones are transitional between zone 1

and zone 2 and are due to rapid lowering of the base-level

within time periods that have been discussed above. The

assumption is made that network adjustments on these zones

is in response to base-level drop.

One can reason, on the basis of Woldenberg's

(1966) pioneering study that a base-level drop of magni­

tude x will cause a network change y by the relation of

equation 4:

y = axb (4)

Equation 4 is a power function which in this context means 57 that the network will allometrically adjust to a base- level fall and adjustment will commence after some threshold value has been reached.

The enigma in solution of this equation has been the problem of selecting a parameter for a network (y in the equation). The present author defines the term

"split-point" as the confluence of Strahler-ordered stream segments of equal order. Split-points are therefore the locations where, in a Strahler-ordered scheme, the order of segments increases by magnitude 1. Thus in a network with a bifurcation ratio of 2, every bifurcation point would be a split-point. Constructing random-walk networks in a manner described by Leopold and Langbein (1962) indicates that the distribution of split-points tends to be random. A corollary of. random distribution is the ten­ dency to have similar density (split-point occurrence per unit area) on consecutive constructions. Over 80 random- walk networks were examined. Apparently, split-point density would satisfy the needs of simple quantification.

The upper part of the Pine Creek network was traced from the 15 minute Pine quadrangle topographic sheet,

Strahler-ordered and split-points delineated (see Fig. 17).

The density of split-points was calculated by using the same grid as used for digitizing. The results show a 58

A - second order split-points O - third order split-points O - fifth order split-points X - non split-point confluences

. 17. Pine Creek drainage network fleft) and split-points (right). 59

disparity in the split-point densities on the four zones

(see Fig. 18). Based on this differentiation, reflecting supposed sensitivity, split-point density was chosen as the parameter to examine Woldenberg's allometric adjust­ ment scheme in a tectonic context. Figure 19, though based on few points, does not contradict Woldenberg's hy­ potheses as applied to the problem of network change. Fur­ thermore, these results provide additional evidence

confirming the reality of these four zones.

Perhaps most interesting at this stage is the

regression line exponent which is less than one. Wolden-

berg had attempted to explain efficiency of space, fitting

hexagons in terms of a maximum bifurcation ratio of 7

(Woldenberg, 1968). The exponent of less than one implies

for many real situations there will be a maximum density

of split-points, which may corroborate the space filling

approach to networks.

Bull and McFadden (1977) note that in tectonically

active mountain fronts, basins tend to be elongated and

become more circular after cessation of tectonism. Fur­

thermore, after cessation of tectonism stream power tends

to approach critical power (Bull, in press) resulting in

valley widening. Elongated basins may be contradictory

to high split-point densities for base-level lowering i. 8 Feunyhsorm fr split-points for histograms Frequency 18.Fig.

NO. SPLIT-POINTS . DENSITY per 250m sq. nte oorpi zones. topographic the on ZONE ZONE (or wface) B)

> H 5 z

1to

RELIEF (ft)

19. Regression equation and line of split-point density as a function of relief. 62

regimes. A possible explanation may be that there is a

lag-time involved in increasing the split-point density.

Assuming the above described relationship between split- point density and relief to be representative,, the hypoth­

esis that valley widening and increased split-point den­

sities are related was tested. Figure 20 implies that

valley widening and split-point densities may be corre­

lated and perhaps in part caused by the tendency to

increase split-point density. Thus the lag-period of

valley widening and split-point density increase may be

similar. Bull (in press) suggests a period of a million

years to widen valley floors in metamorphic rock of arid

regions.

These results indicate that zones 1-t and 2-t are

separated by a period of stability of base-level that

lasted at least a million years.

Denudation and Network Change

Denudation is a measure of the material removed

from a drainage basin. Many factors may influence the

rate at which this process proceeds including relief

(Anhert, 1970), lithology (Schumm and Chorley, 1966),

and climate (Langbein and Schumm, 1958; Wilson, 1973;

Gregory, 1976; Douglas, 1976). Recognizing the multi­

variate nature of denudation, matters may be simplified 63

RELIEF (ft)

Fig. 20. Regression equation and line of valley widening is a function of relief. 64 by considering the denudation rate a reflection of the realized demand for sediment within a drainage basin.

Changes in the denudation rate may be due to fire, con­ struction activities, logging, etc. Regardless of how these agencies interreact with lithology and climate, the result will be noted as a change in denudation or a change in the realized demand for sediment.

Sediment will be supplied to the mouth of a drain­ age basin by the sum work of the existing channel network.

Woldenberg (1968) compares networks to marketing systems where there is a tendency towards maximizing the effi­ ciency of supply. One may wonder therefore, about the relationship of supply and demand in the Pine Creek drain­ age basin.

Anhert (1970) demonstrated that denudation data could be fitted by a linear relationship, or that the rate of denudation is directly proportional to relief.

The high correlation coefficient observed by Anhert justi­ fies using this relationship to define (only) a tendency that exists at any one particular time. This report has used split-point density as a measure of network change and thus will be used as an index of sediment supply rates.

The nature of the supply and demand curves is il­ luminating. The supply curve is a power function (equa­ tion 4) with an exponent of less than 1.0. Plotting these 65 curves (see Fig. 21) shows that there are two intersec­ tions. The intersection in the lower left of the graph represents an equilibrium between supply and demand of sediment. Feedback mechanisms near the equilibrium point tend to re-establish or establish equilibrium. For ex­ ample, if relief of a drainage basin is increased to a value at point A, demand will increase linearly while split-point (supply) density will increase at a faster rate. This initiates a feedback mechanism by which the mean slope increases and in turn increases demand. This is a self-enhancing feedback mechanism which tends towards equilibrium. Above the equilibrium point is a self-- regulating feedback zone. In the lower part of this zone supply can increase at a much faster rate than demand which tends to minimize morphologic change. A large storm may increase demand for sediment by the network can expand or contract rapidly near equilibrium. A logging or defo­ liation program may however shift the demand curve and therefore establish a new and different equilibrium which will be approached rapidly. The curve's intersection in the upper right of the graph represents a threshold.

Above this threshold demand can increase at a faster rate than supply. A change in any number of variables, such as tectonic base-level fall, may push demand beyond this PI-ON DENS SPLIT-POINT

RELIEF (REALIZED) network's.split-point adjustments (curve). S demand for sediment (straight line) and a drainage Fi#' Fi#' 21. Possible relationship between denudational

NOLLVOnNaO 67 threshold. Above the threshold a small increase in demand initiates a network change that occurs at a very slow rate.

This may be due to space-filling constraints (Woldenberg,

1968), One should note that on erodible materials the demand function may have a significantly steeper slope which in effect lowers the threshold value and the rate of network response. Lower threshold values would be obtain­ able by smaller perturbations and initiate more rapid network expansion. Conversely, decreasing demand below equilibrium on erodible materials would initiate a rapid decrease in split-point density causing rapid backfilling of channels (perhaps in response to climatic variations as in Schumm, 1956). An analogous relationship may be true for longitudinal profiles. Leopold and Langbein

(1962, p. 4) note that "... relatively short intervals are needed to reach a state approaching the maximum probable, although the rate of adjustment to the theoretic most probable state thereafter may be quite slow if ever

achieved."

Rate of Denudation and Scarp Retreat

Denudation rates were calculated for the Pine

catchment from the town of Pine northward. The volume of material removed was assumed to be equal to the mean volume of material removed per unit area, between zone 1 68 and zone 2. This volume per unit area was then averaged over 12 m.y. The results indicate that denudation has proceeded at an average rate of 5 cm per thousand years for the Pine canyon area. Since denudation has continued on topographic zone 1, the denudation rate of 5 cm per thousand years is a minimum value.

Using the rate of denudation of 5 cm per thousand years, it is a simple geometrical exercise to calculate the rate of scarp retreat, though one must assume a mode of retreat. In this case parallel retreat is the likely mode. An idealized slope profile was constructed (see

Fig. 22) on graph paper. Knowing that in one million years the mean denudation would be 50 meters it is a straight­ forward construction to trace on the same graph the scarp after it has retreated. Forty vertical lines were drawn in to illustrate the amount of land surface lowering distrib­ uted along the profile. The average length of these lines is equal to the average denudation, thus one"can- calibrate the units on the graph paper. Using the dimensional value of the units one.simply measures the amount of retreat on the graph. In this case the Mogollon Rim has been retreat­ ing at an average rate of 354 meters per million years.

Maximum denudation in this example is more than twice the mean denudation (128 meters). Using this minimum rate of :::::::

Geometric construction used to calculate scarp retreat from denudation rates. Ox to 70 scarp retreat, the Mogollon Rim would be just north of the Diamond Rim fault 30 million years ago. Extrapolation beyond 30 m.y. is not advised since rim gravels were still being deposited on the plateau.

The geometrical construction used is sensitive to the overall slope angle chosen to represent the scarp.

The steeper the overall scarp slope used, the smaller the rate of scarp retreat for a given denudation rate and the larger the denudation rate for a given value of scarp retreat. The relationship between overall scarp slope, denudation rate and scarp retreat can be approximated by equation 5 for parallel retreat.

R = 2D/tan& (5) where R is the rate of scarp retreat, D is the denudation rate and 6 is the overall scarp slope in degrees. Thus scarp retreat is dependent on the average lowering of a land surface along given slope. The rate of scarp retreat is not directly dependent on scarp height though the denu­ dation rate may be dependent on scarp height.

Bracketing values of escarpment retreat and denu­ dation can be approximated by solving for D in equation 5.

A maximum value for the rate of retreat on the Mogollon

Rim may be calculated by measuring the Rims' average distance from the Diamond Rim fault and dividing this value by the age of the capping basalt (12 m.y.) plus pedimentation time (2 m.y.). The maximum value of Rim retreat so calculated is 857 meters per million years, which according to equation 5 would mean that denudation along the Mogollon Rim proceeded at a rate of 115 meters per million years. The maximum values for scarp retreat and denudation are therefore more than twice the minimum values of 354 meters per million years for scarp retreat and 50 meters per million years for denudation.

Preliminary Evaluation of Post Miocene Tectonic Activity Along the Diamond Rim Pault Near Pine

Hillslopes with identical boundary conditions

(i.e., base-level and lithologic sequence) should have a characteristic slope value which, when studied over a small area, should vary with credibility of the rock- type. Certain formations may be slope formers and others ledge formers.

In order to define a central tendency of slope i values on each rock type a compositing (or overlay) method was used. The topographic map of the study area

(part of the Buckhead Mesa 7.5 minute quadrangle) was digitized by overlaying a grid and sampling every one hundred meters for elevation. These elevations were punched onto computer cards. Computer programs were 72 written in FORTRAN IV by the author to take the data and output line-printer inventory maps. Line-printer # maps are inexpensive and require no special hardware. The computer program COMPOS does the actual printing and is listed and explained in the Appendix.

Another FORTRAN program, SLOPE, was written to con­ vert the topographic map into a slope map. The program algorithm moves from one grid position to the next position along rows. At each position the eight adjoining cells are tested to obtain the maximum elevation difference. The program uses this maximum difference to calculate the slope for that grid position. This operation continues until all of the data (except the edges) have been pro­ cessed. Program SLOPE is listed and documented in the

Appendix.

Line-printer inventory maps for topography and slope (see Figs. 23, 24) represent 3360 points and each line printer character represents a 100 mty 100 m square.

Errors that are not corrected will be transmitted through the compositing process (see framed area, Figs. 23-26).

A section of the geologic map was also (see Fig.

25) digitized in order to facilitate an inventory of slope on particular rock units. A third separate FORTRAN pro­ gram, named ADD, was written to perform the actual :@X%xZ M^OXg-

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26. Computer line-printer inventory jnap showing slopes greater than their mean value on a particular rock type. 77 compositing. Program ADD overlays one map on another and creates a file containing the composite map. The program user can group data or filter data as the purpose demands.

The mean slope for a particular rock type was used as the index of a central tendency or adjustment. Slopes higher than their mean value for particular geologic formations are displayed in Figure 26. Having a slope index for rock type enables one to examine slope values that are high (or low) which cannot be explained by rock type. The difference between the actual slope and the central ten­ dency is called a geomorphic residual (equation 6):

GR = S - S (6)

If GR is positive, the residual is described as a positive geomorphic residual and if GR is negative then it's a negative geomorphic residual. In the case where boundary conditions do not vary, positive geomorphic residuals

imply base-level fall and negative geomorphic residuals

imply formation of planar surfaces during base-level

stability (in the past possibly).

The areas of positive geomorphic residuals can be

divided into three separate domains. One domain lies

adjacent to the downcutting Pine Creek. A second lies underneath a basalt flow. The third domain lies on the 78 upthrown side of a major fault and just north of its

trace. Domain one may indicate a lowering of base-level

in Pine Creek. Domain two is likely due to the basalt

caprock. Domain three cannot be explained in terms of

boundary condition changes unless one infers movement on

the fault, and is thus termed a geomorphic anomaly. While

there is no surviving fault scarp the anomaly may repre­

sent fault movement. The other boundary is the top of the

hill where downwasting may have exposed a unit that be­

haves as a caprock.

Though it is impossible to conclude whether or not

tectonism has resulted in the geomorphic anomaly of domain

three, the general procedure remains a useful tool to gain

insights as to the variables and processes involved.

Pine Creek is the longest stream in the study area

and traverses the major fault. A longitudinal profile

(see Fig. 27) clearly reveals an abrupt steepening of

channel slope about 1500 m north (upstream) of the fault.

Without geologic information this feature could be inter­

preted as a tectonic nickpoint. Actually Pine Creek tra­

verses quartzites of the Mazatzal Formation, forming a

series of waterfalls. The data are therefore somewhat

equivocal as to the origin on the nickpoint.

Using equation 3, SL values were calculated for

reaches of Pine Creek from headwaters to well downstream 1000 10000 DISTANCE FROM HEADWATERS (X3.3 ft)

Fig. 27. Longitudinal profile of Pine Creek channel plotted on semi- logarithmic graph; SL values are calculated for each reach along the profile. to 80 of the fault. The channel reach that contains the nick- point has a high SL value. The dilemma is, how much of

the SL value is merely due to the quartzite steepening

the channel and how much, if any, is tectonically induced.

The procedure adopted to solve this dilemma was to

assume that the SL values of Pine Creek downstream from the

fault were representative of a channel slope adjusted to

flowing oh quartzite. The SL values of five reaches below

the fault were averaged. From equation 3, we have:

H2 = H1 - ST(lnL2-lnL1) (7)

where H 2 is now the elevation of the channel at the end of

a reach and ST is the value assumed to reflect and adjusted

channel slope. The difference in elevation between the

actual channel elevation and the calculated litholog­

ically adjusted channel elevation (H2) may reflect the

magnitude of a tectonic displacement(s) (equation 8):

D = (Hi-ST(lnL2-lnLi))-H2^ (8)

D represents possible tectonic displacement. Using the

values from Pine Creek,

D = (5250-2473(Inl3500-lnl2500))-5000

D = 5060-5000 = 60 ft or 18 m

The result, at first glance, implies a minimum of 18 meters 81 elevation difference that cannot be explained by the resis­ tant nature of the quartzite in the channel. The

"fortuitous" location of the fault allows one to suggest tectonism. Perhaps 18 meters of the fault displacement(s) have not been allowed to disappear because the quartzite is retarding recession of the nickpoint. Although this data is highly suggestive of faulting and constitutes a positive geomorphic residual, there may be other variables that can account for this feature. At the point Pine Creek begins to traverse the quartzite, it starts to pick up quartzite bed load. The quartzite load is more efficient in eroding the channel than the sedimentary debris derived from the

Paleozoics, thus the value of D may only reflect a transi­ tion in the nature of the bed load. Unfortunately, I know of no way to practically test this hypothesis, thus the value of D can be considered a geomorphic anomaly.

Conclusions

Near Pine, Arizona, four distinct topographic zones exist which are called, 1, 1-t, 2, 2-t. Portions of zones

1 and 2 are preserved by basalts, thus their altimetry represent pre-basaltic configurations. Zones 1-t and 2-t can be fixed only relative to zones 1 and 2. The minimum ages of zones 1 and 2 inferred from the basalts are 14 m.y. and 12 m.y. respectively. The maximum age of zone 1, 82 based on denudation and scarp retreat methods, is about

25 m.y. Since basalt flowed south on zone 1 from Baker

Butte, and the zone decreases in elevation from north to south, it can be inferred that drainage, was also flowing southward. Thus the maximum age bracket for establishment of south flowing streams (at least locally) is 25 m.y.

Topographic zone 1-t, which formed sometime between the inception of zone 1 and the basalt flows on 1 zone 2 marks the tectonic drop in base-level. Rapid base- level fall initiated drainage network change witnessed by increased split-point density. Base-level fall appears to be related to faulting along the Diamond Rim fault. The upper boundary of zone 1-t generally coincides with the drainage basin boundary in the Pine Creek headwaters while in other places it coincides with the Mogollon escarpment.

This allows one to use the denudation rate from the Pine

Creek watershed to represent the denudation rate along the

Mogollon Rim (locally).

Faulting had waned sufficiently by 15 m.y. ago to allow pedimentation to occur. Pedimentation is represented by topographic zone 2. Following basalt flows on zone 2

(12 m.y. ago) base-level again' dropped (but this time occurred south of Buckhead Mesa) which initiated zone 2-t and its high split-point density. 83 The rate of scarp retreat based on denudation rates yields -a minimum value of 354 m/10^years. The rate of scarp retreat based on scarp distance from fault yields a maximum value of 857 m/10^ years. Denudation rates corresponding with these scarp retreat rates are

50 m/10^years and 115 m/10^years respectively. According to the minimum rate of scarp retreat, tectonic base-level fall may have commenced 30 m.y. ago.

Geomorphic anomalies are present on hillslopes and channels above the Diamond Rim fault which may imply

Quaternary tectonism. The equivocal and subdued nature of the anomalies, however, lead me to infer that none of the possible tectonism is Holocene. CHAPTER 4

TECTONIC IMPLICATIONS OF MOGOLLON RIM DEVELOPMENT

Can the evolution of the Mogollon Rim be related to regional tectonics? The regional nature of the Mogollon

Rim and the relationship of the Mogollon Rim near Pine to base-level fall south of the escarpment and faulting along the escarpment suggests a connection between the Mogollon

Rim and tectonically controlled base-level. From the data presented above, it would appear that the history of the

Mogollon Rim began in the mid-Tertiary. Therefore, I feel it would be useful to review the present geophysical signature of Mogollon Rim country and explore possible ties between mid-Tertiary tectonics, geophysical character­ istics and Mogollon Rim development.

Geophysical Setting

The present crustal configuration in Arizona can be schematically outlined from existing geophysical studies

(see Fig. 28). Seismic-refraction surveys by Warren (1969) show that from Gila Bend to the Mogollon Rim, crustal thick­ ness increases from about 22 .kilometers to 37 kilometers thickness near Winslow. A series of seismic-lines nearly

84 85

110° 00’ 33*00'

I

32*00' 112*00 CONTOU* - 20011 (Aim) KIIOMITIRS

Fig. 28. Subenvelope map of Tucson 2° sheet, 86

PRESENT

EXPLANATION

SEISMIC LINES

/ GRAVITY TRANSITION

CORf COMPLEX DISTRIBUTION

ca. 2S m.y. ago SEISMIC BELT

CRUST

LOCATION OF FIG, 28 a s 2 7 0 km Is s 3 6 0 km

SUBDUCTED LITHOSPHERE

Fig. 29. Location map showing characteristics of Mid-Tertiary extensional zone. 87 perpendicular to the Gila Bend-Mogollon Rim lines, show crustal thickness to vary about a 36 kilometer value.

Thus crustal thickness contours trend north-northwest in central Arizona.

Sumner, Schmidt and Aiken (1976) note a transition zone from zero free-air gravity values to more negative values. This zone trends approximately along 110° 30W longi­ tude. They interpret this transiton zone (Sumner et al. ,

1976, p. 11) as demarcating fundamentally different litho­ sphere. Sumner (1976) delineates a belt of seismicity in

Arizona that coincides with the free-air gravity transition zone and trends north-northwest. Of interest is the topo­ graphic expression of this transition. A geomorphic tool to examine such regional' topographic elements is an isopleth map of stream channel elevations, or a subenvelope map.

The subenvelope map of the Tucson 2-degree topographic sheet illustrates the physiographic contrasts across this zone (see Fig. 28). Studies of seismicity by Smith (in prep;) reveal a belt of seismicity peripheral to the

Colorado Plateau. The geography of this seismicity may be due to the rigid nature of the plateau crust relative to its neighbors. Sumner’s^ seismic transition zone in southeastern Arizona may therefore be a diffuse splay of this seismic belt. 88 Other seismic studies (Julian, 1970) have shown that the seismic low velocity zone in the upper mantle is thicker and shallower under the Basin and Range and deeper and less developed under the Colorado Plateau. Geophysical models by Porath (1971) reveal a ridge of highly conductive

(2 OHMmeter) material running 15 km beneath the Colorado

Plateau-Basin and Range transition zone, essentially coin­ ciding with the Wasatch Line in Utah. A similar (but deeper) ridge may underlie the Rio Grande rift zone.

Tectonic Setting

During the early-to mid-Tertiary two major litho­ spheric plates, the Pacific and Farallon plates, separated by the East Pacific ridge and various transform faults lay west of the American plate (Atwater, 1970). The Farallon plate, which likely consisted of hot (young) oceanic litho­

sphere, was being subducted along a trench on the western margin of North America at a rate faster than its rate of

formation. Subduction along the trench occurred at a

shallow angle, perhaps 20°, which in the southern

Cordillera resulted in arc magmatism nearly 1000km inboard

of the trench during the mid-Tertiary (Coney and Reynolds,

1977; Keith, 1978). Calc-alkalic magmatism is associated

with the subduction of the Farallon plate (Christiansen

and Lipman, 1972). 89

Within the arc terrain, lies a zone of uietamorphic core-complexes (see Figs. 1, 29}. Metamorphic core­ complexes are now thought to represent "mega-boudinage" features (Davis, 1978) or crustal necking due to extension.

During their mid-Tertiary history, core-complexes formed uplifts off which gravity-gliding took place (Davis, 1975,

1977). Ignimbrites with high initial strontium 87/86 ratio, indicating crustal contamination or origin (Damon, 1971) where extruded in volumnous quantities and often flank the core-complexes in Arizona (Davis and Coney, 1979). The ignimbrites and the resetting of K-Ar clocks of Precambrian age rocks to mid-Tertiary ages (Damon, oral communication,

1977) in parts of southeastern Arizona bear witness to a dramatic thermal event. Contemporaneously, basins were forming depocenters for Pantano Formation and equivalents.

Sometime between 30 m.y. ago and 24 m.y. ago

(Atwater, 1970; Nilsen and Clarke, 1975) the East Pacific spreading ridge intersected the subduction zone causing a change in plate configuration and initiating the San

Andreas transform fault. By late Tertiary time magmatism became predominantly basaltic (Shafiqullah et al., 1978).

A study of orientations of mid-Tertiary (<30 m.y.) dikes, veins and stocks (Rehrig and Heidrick, 1976) suggest a fundamental "stress" direction change from compression in 90 the Laramide to extension during the mid-Tertiary. The extension directions parallel Sumner's transition zones.

Interestingly, there appears to be a sequence in the nature of the extensional faulting. Early core-complex faulting has been described as "ductile normal faulting" (Davis,

1978). Following this faulting was a period of normal faulting accompanied by block rotation. I interpret the block rotation to signify listric normal faults. The period of listric normal faulting essentially ceased by

15 m.y. ago in southeastern Arizona (Shafiqullah et al.,

1978) and by 13 m.y. ago in southwestern Arizona (Eberly and Stanley, 1978). Following the period of listric normal faulting, extension was characterized by high-angle normal faults.

The extensional zone in Arizona is characterized by the general geographical coincidence of (see Fig. 29)

1. Sumner's gravity and seismic transition zones

2. Significant physiographic transition

3. The gradient of crustal thickening

4. High geothermal gradients

5. Metamorphic core-complexes

6. Rapid geochemical transitions for rocks between

29-22 m.y. from high K calc-alkalic to alkali-

calcic (Keith, 1978) 91

7. Steep gradients in K-depth to Benioff zone for

rocks between 29-22 m.y. old (Keith, 1978).

Similar relationships may be true for areas to the north of Arizona. Blackwell, for example, (after Smith, in preparation) has mapped a linear zone of high thermal ener­ gy that parallels the north-south zones of, seismicity, thin crust, and low Pn velocity mantle along the eastern

Great Basin-Colorado Plateau transition zone.

Tectonic Interpretations

The data reviewed above suggest that the subducted lithoshperic slab was ruptured or fissured along a zone that was characterized by uplift and extension in the mid-

Tertiary (see Fig. 29). The rupture(s) may represent zones of weakness in the subducted lithosphere which opened up when active subduction along the trench ceased, after the initiation of the San Andreas fault.

Anomalous mantle (low Pn velocity) may have prefer­ entially traversed the lithospheric slab by way of the fissures, resulting in a diapiric upwelling and convective heat flow regime that was initially geographically local­ ized by the fissures. The transition from somewhat ductile extension of the core-complex type, through a period of listric normal faulting to normal faulting can be explained

in terms of the cooling off of the mid-Tertiary thermal 92 event in a "continuous" extensional environment. The exten­ sion was initially caused by upper mantle diapirism but as the San Andreas system grew, oblique extension propagated eastward from the Pacific-American plate boundary became dominant. The transition period between listric normal and normal faulting was accompanied by a relative lull in volcanism. This lull in volcanism between 18 m.y. to about

13 m.y. ago is apparent in the Mountain Region of Arizona

(Shafiqullah et al., 1978) but is even more apparent in

New Mexico (Chapin and Seager, 1975).

Structural studies in progress in southeastern

Arizona may provide orientation data from faults and slick- ensides that show a distinct change in preferred fault orientations from the mid-to late-Tertiary (Menges, person­ al communication, 1978) suggesting the timing and orien­ tation of diapir and San Andreas extension can be discerned.

The timing of the transition between mantle upwelling and oblique extension should get younger to the north as the San Andreas system extended northward.

The geographic coincidence as well as the similar

ages for the extensional zone and initial drainage reversal

along at least one section of the Mogollon Rim is very sug­

gestive of some sort of connection. The Mid Tertiary extension and basin formation may therefore provide a straightforward mechanism to account for tectonic base- level fall along and south of the present Mogollon Rim. CHAPTER 5

SUMMARY OF THE EVOLUTION OF THE MOGOLLON RIM NEAR PINE

During Eocene-01igocene time drainage was flowing northward from the Basin and Range province into the

Colorado Plateau in Arizona (see Fig. 30) while at the

western margin of North America the Farallon plate was

being subducted along a trench. In Miocene time (between

30 and 24 m.y. ago) the East Pacific ridge began to inter­

sect the trench which resulted in the initiation of the San

Andreas fault,' that is to say plate motions were accommo­

dated by strike-slip movement instead of subduction. Com­

pression, associated with subduction, ceased first in the

southern Cordillera and then northward as the San Andreas

grew. When compression ceased, mantle with anomalously

low Pn velocity began to rise through ruptures or fissures

in the remnant subducted lithospheric slab.

Above the rising diapirs, local uplifts and basins

formed. At this stage in their evolution metamorphic core­

complexes represented topographic highs off which gravity

gliding took place. The rock fabric (which may be substan­

tially older) within the core-complexes is thought to

reflect extension related to mega-boudinage. Tremendous

94 S5W NNE DRAINAIM DIRECTION

30 my* ago

INITIAL DRAINAGE ZONC I

25 my. ago

ANCESTRAL MOOOLLON RIM

DIAMOND

BASALTS

PEDIMENT

12 my. ago

CANTON CUTTING

present

Fig. 30 • Schematic cross section's showing development of Mogollon Rim near Pine. 96 quantities of ignimbrites were extruded simultaneously with core-complex emplacement.

Mid-Tertiary basin formation resulted in reversal of drainage from north flowing to south flowing about

25 m.y. ago. The location of the divide separating north

and south flowing drainage in the mid-Tertiary approxi­ mately coincides with the present Mogollon Rim, at least

locally. Sometime between 25 m.y. ago and 15 m.y. ago,

crustal extension and faulting along the Diamond Rim

fault had waned enough to allow retreat and pedimentation

of the fault scarp, which at that time had relief compara­ ble to the present relief on the Mogollon Rim. The average denudation rate along the escarpment

has been between 50-115 m per million years resulting in

escarpment retreat at a rate between 354-857 m per

million years.

In late-Miocene (12 m.y. ago) basalts flowed over

the pediment and fault. Following or accompanying the

basalt extrusion, base-level again fell initiating canyon

cutting into the pediment. The location of the base-level

fall lay to the south of Buckhead Mesa and may be related

to local faulting or may be related to events in the Verde

Valley. Post 12 m.y. old faulting along the Diamond Rim

fault is minor, none of which appears to be Holocene. programs is 110K for a 10,000 cell matrix. Execution time Execution matrix. cell 10,000 a for 110K is programs computer CDC ofArizona’s University the on developed were by the present author. Maximum core requirements for these for requirements core Maximum author. present the by is less than 2 seconds. An average cost for a computer run computer a cost for average An seconds. 2 than lessis is around $1.00. is around C NCAT=NUMBER OF CATEGORIES OF NCAT=NUMBER C nnnononnnnnnnn 4 OMT” ,I2,2X,I2) FORMAT(”” 14 DIMENSION CAT(20) DIMENSION DIMENSION DATA(100,100) DIMENSION DIMENSION SYMBOL(3,20) DIMENSION A=UBRO AEOISTA AAWL E DIVIDED BE DATA WILL THAT CATEGORIES OF CAT=NUMBER PROGRAM COMPOS(INPUT,OUTPUT,TAPE5=INPUT,TAPE6=OUTPUT) PROGRAM PROGRAM COMPOS LARRY MAYER LARRY COMPOS PROGRAM XMAP(100,100) DIMENSION WRITE(6,11)NCAT SYMBOL=THE LINE PRINTER CHARACTER(S) TO REPRESENT TO CHARACTER(S) PRINTER LINE SYMBOL=THE XMAP=THE DIMENSIONS (IN CELLS) OF THE DIGITIZED MAP. DIGITIZED THE OF (INCELLS) DIMENSIONS XMAP=THE DATA”THE SIZE OF THE (MAXIMUM) MATRIX CONTAINING THE CONTAINING MATRIX (MAXIMUM) THE OF SIZE DATA”THE WRITE(6,12)(CAT(I),I=1,NCAT1) NCAT1=NCAT+1 RT(,4 NROW,NCOL WRITE(6,14) READ(5,10)NCAT READ(5,15)(CAT(I),I=1,NCAT1) ED52) NROW.NCOL READ(5,20) The computer programs listed and documented below documented and listed programs computer The GEOPHYSICAL ANOMALIES OR DIFFERENT ROCK UNITS. ROCK DIFFERENT OR ANOMALIES GEOPHYSICAL INTO. THESE MAY BE TOPOGRAPHIC ELEVATIONS TOPOGRAPHIC BE MAY THESE INTO. DIGITIZED MAP. DIGITIZED PROGRAM LISTING.AND DOCUMENTATION LISTING.AND PROGRAM EACH CATEGORY. THE USER MAY SELECT UP TO UP SELECT MAY USER THE CATEGORY. EACH THREE LINE PRINTER CHARACTERS FOR EACH FOR CHARACTERS PRINTER LINE THREE OVERPRINTING ALLOWS GRAY SCALE USAGE. SCALE GRAY ALLOWS OVERPRINTING CATEGORY, WHICH WILL BE OVERPRINTED. BE WILL WHICH CATEGORY,

APPENDIX

UNIVERSITY OFARIZONA UNIVERSITY

97 TUCSON,AZ,85704

C 7/8/9 GOES HERE GOES 7/8/9 C n o o n 1001 FORMAT("+",6 FORMAT("+",6 1001 0A1) ",60A1) FORMAT(" 1000 400 CONTINUE 400 401 CONTINUE 401 CONTINUE 200 402 CONTINUE 402 0 CONTINUE 201 0 CONTINUE 202 100 CONTINUE 100 0 CONTINUE 60 0 CONTINUE 50 0 FORMAT(10X,II) 10 30 FORMAT(5(Al)) 30 FORMAT(F7.2) 15 3 OMT" ",5A1) FORMAT(" 13 12 rFORMAT '',11)(" " FORMAT(" 11 ,F7.2) FORMAT(14X,I2,9X,I2) 20 FORMAT(10(F7.2,IX)) 1 CTK1) XMAP(I,J)=SYMBOL(l,K) +CAT(K+1)) CTKl) MPI,J)-SYMBOL(3,K) XMAP(I +CAT(K+l)) XMAP(I,J)“SYMBOL(2,K) +CAT(K=l)) RT(,3 (SYMBOL(I,J),J=1,NCAT) WRITE(6,13) OCAG TI STATEMENT. THIS CHANGE TO FORMAT IN GIVEN IS DATA THE OF FORMAT THE 1=1,56 60 DO RT(,00 (XMAP(I,N),N=l,NCOL) WRITE(6,1000) ED53) (SYMBOL(I,J),J=1,NCAT) READ(5,30) 1=1,3 50 DO DO 400 K=1,NCAT 400 DO 1=1,NROW 100 DO RT(,01 (XMAP(I,N),N=1,NCOL) WRITE(6,1001) K=1,NCAT 401 DO J=l,NCOL 201 DO DO 200 J=l,NCOL 200 DO SURE BE FORMAT, THE ALTER 1. TO STATEMENT (DATA(I,J),J=1,60) READ(5,1) O42 K=1 402 DO ,NCAT' J=l,NCOL 202 DO F DT(,) G. A() AD DT(,) .LT .AND. DATA(I,J) .GE. CAT(K) (DATA(I,J) IF RT(,01 (XMAP(I,N),N=l,NCOL) WRITE(6,1001) F DT(,) G. A() AD DT(,) .LT .AND. DATA(I,J) CAT(K) .GE. (DATA(I,J) IF F DT(,) G. A() AD DT(,) .LT .AND. DATA(I,J) .GE. CAT(K) (DATA(I,J) IF END STOP

' 99

The format of the control cards is illustrated in

Figure 30. The cards following "THERE ARE 16CATEGORIES" are the lower and upper limits for each category in sequence. Thus the first category contains all values greater or equal to 10.0 but less than 10.8; the second, greater or equal to 10.8 but less than 20.0; the third, greater or equal to 20.0 but less than 20.6 etc. The symbols for printing (last three cards in Figure 31) are overprinted. Thus for category 4 (column 4) a "D" and will be overprinted while for category 8

(column 8) a "=" and " q " will be overprinted.

Program ADD is a utility that sums two digitized maps and punches the composite onto cards for use with program COMPOS. Program ADD can easily be modified to output data such as areal coincidence of map units and basic statistics of the distributions. In its present from ADD divides the scored composite map into eight categories. The number of categories may be expanded by changing the appropriate DIMENSION statement and DO statements.

PROGRAM ADD(INPUT,OUTPUT,PUNCH, TAPE5=INPUT +TAPE6=OUTPUT,TAPE7=PUNCH) DIMENSION CATEGS(9) DIMENSION COUNT(8) DIMENSION CATAVG(8) DIMENSION CATSUM(8) DIMENSION DATA1(100,100) . N + ' •’« s 4 % % 7 |vs *mi •mBaoi«ii»rty#i®soseMn»4 »ss«i»w$s40 4»4i%*4 4 «e«<4T«e4ectsi to a » a »* a t* +j t* r* ja

t»»«iSMST *ss• **-!*.

fKr"rMTR7!i"is,!.?.V,?.Lr.... »f Bnux b y s b L: n u L _ _t ______: u l/r o. ------COS 5.30 ------"*

0 0 7 0 . 4 3 ------U07U. 0 0 6 0 . 5 0 ' ...... 0060.______■ 0050." 50______J______U050. '0040.50 0040. ------.0030.5.0 0030. i s ? 4 - 'ouiot'5'1' ----- THERE "ARE j aCATEGOR IE3 '

<5 ■ « i 4 > » r t tetuaiSHeerTft ew'»nu»«t»»Ft7*a»ao3«MX3>4»»ii 37 3e>»«o*«a*e**«<4r*«e:6#«2n i i j 4 » • 7 • • * ii sis m % » »7 • *teatyoieaMvzar4Sosi»ss>4SiMS7w»«

OOOOOOCUOOOOOOOOOOOCOOOGOOOOOOOCCOOOOOOOOCOOOOOOOOOOO i » i « i i 7 i

6 6 6 S 6 B 6G B B B £ G 6 6 6 6 6 B 6 B G 6 8 6 6 6 E B G S G B G G B S G 6 S 6 6 G 6 S £ S G GB 6 8 B i i i i s i i i «tinanwnw 17w a 2» a a a 2< a a a a a r t a a a i < « x a a a 4 « 4 i <7 47<441<4<74i

[ 8 8 8 8 8 8 8 8 8 8 8 J 3 8 8 8 E J 8 8 8 8 8 ? 8 8 8 J 8 8 8 8 3 8 J 8 8 8 8 8 8 3 8 8 8 8 8 8 8 S S 8 1 2 3 4 5 1 7 1 S l§ n D O K tt IS H 13 IS 29 21 a a 24 25 2127 219 J9 j l l i 33 34 M S n S31 48 41 42 4344 454S 47 414S56 51 52 53 []99999999S9998S9995399999999339939g9999999S939999999S 3:45171 I 11H121314 fj ^ T7 IS il J3 21 22 22 2< 25 tS Zi 7123 M 31 3? 73 24 35 2S T» j; 3* 40 <1<2 C 44 4f 47 4MS S3 51 52 IT ______25«___srs«es«D_Foww______1______— ------

Fig. 31. Control statements used in execution of program COMPOS. C READ DATA FROM SECOND DIGITIZED MAP DIGITIZED SECOND FROM DATA READ C C ADD TWO MAP WEIGHTS TO SCORE NEW MAP NEW SCORE TO WEIGHTS MAP TWO ADD C C READ DATA FROM FIRST DIGITIZED MAP DIGITIZED FIRST FROM DATA READ DIVISIONS MAP SUPPLIED CATEGS=USER C C C CLUAEMA AU I OBND CATEGORY COMBINED IN VALUE MEAN CALCULATE C n n n n n 500 CONTINUE 500 3 FORMAT(13,IX,13) 333 4 CONTINUE 54 1 FORMAT(10(F7.2,IX)) 11 51 CONTINUE 51 53CONTINUE 52 CONTINUE 6 CONTINUE 56 57 CONTINUE 57 5 CONTINUE 55 FORMAT(10(F7.2,IX)) 1 FORMAT(FS.2) 3 CTG(+) COUNT(K)=COUNT(K)+1 +CATEGS(K+l) CTG(+) CATSUM(K)“DATA(I,J)-CATEGS(K)+CATSUM(K) +CATEGS(K+l)) O 1 1=1,NROW 51 DO TEST AND CALCULATION LOOP CALCULATION AND TEST DO 500 K-1,8 500 DO DATA(I,J)=DATA1(I,J)+DATA2(I,J) O 2 1=1,NROL 52 DO ED51) DT2IJ ,J=1,NCOL) (DATA2(I,J) READ(5,11) DIMENSION DATA(100,100) DIMENSION O 3 1=1,NROW 53 DO COUNT(K)=0 54 J=1,NCOL DO ED53 (CATEGS(I),1=1,9) READ(5,3) DIMENSION DATA2(100,100) DIMENSION O 5 1=1,NROW 55 DO FREQUENCY IS THE COUNT CATSUM(K)=0 ED51 (DATA1(I,J),J=1,NCOL) READ(5,1) ED533 NROW,NCOL READ(5,333) O 57K=1,8 DO 1=1 56 DO ,NCOL O AHCTGR INMAPI CATEGORY EACH FOR MAPS OF WEIGHTS OF CATSUM=SUM CATAVG(K)=CATSUM(K)/COUNT(K) +++ O 61K=l,8 DO FDT(,) G. AESK .N. AAIJ .LT. .AND. DATA(I,J) .GE. CATEGS(K) IF(DATA(I,J) FDT(,) G. AESK .N. AAIJ .LT. .AND. DATA(I,J) .GE. CATEGS(K) IF(DATA(I,J)

101

102

TOPOG(I+1,J)) TOPOG(I+1,J+1)) TOPOG(I,J-l)) TOPOG(I,J+l)) TOPOG(I+l,J-l)) TOPOG(I-1,J-1)) T0P0G(I-1,J+l)) TOPOG(I-1,J))

Program SLOPE calculates an approximate slope TOPO(6)= ABS(TOPOG(I,J) TOPO(7)= ABS(TOPOG(I,J) TOPO(8)= ABS(TOPOG(I,J) TOPO(9)= ABS(TOPOG(I,J) TOPO(l)= ABS(TOPOG(I,J) TOPO(3)= ABS(TOPOG(I,J) TOPO(4)= ABS(TOPOG(I,J) TOPO(2)= ABS(TOPOG(I,J) DO DO 20 1=2,55 CALCULATE THE LOCAL RELIEF DO DO 10 J=2,59 READ(5,11) READ(5,11) (TOPOG(I,J)J,=l,60) DIMENSION TOPOG(56,60) DO 100 1=1,56 DIMENSION SLOPE(56,60) PROGRAM SLOPE(INPUT,OUTPUT,TAPE5=INPUT,TAPE6=OUTPUT) DIMENSION TOPO(9) STOP DO DO 1701=1,NROW END WRITE(6,1000) K,CATAVG(K) WRITE(7,171) (DATA(I,J),J=l,NCOL) + 15, 'IS' ,F20.10) 'IS' 15, + 11 11 FORMAT((10(F5.0,3X))) 61 61 CONTINUE 100 100 CONTINUE 171 171 FORMAT(10(F7.2,IX)) 170 CONTINUE 1000 FORMAT(' ' ,4(/) , ' MEAN MAP2 ' VALUE FOR CATEGORY', , ,4(/) 1000 FORMAT(' ' coarse grid may be used. approximations a fine gridmust be used for digitizing. C C PUNCH COMPOSITE MAP ON CARDS FOR based on interpolation from the digitizinggrid. For good C C PRINTING BY PROGRAM COMPOS To To look at generalized slopes (not a real slope map) a u u u the DIMENSION statements and DO loops will have to be to have will loops DO and statements DIMENSION the given size matrix. To use SLOPE with other sized matrices sized other with SLOPE use To matrix. size given adjusted. n n n n o o n 0 CONTINUE 200 0 CONTINUE 300 0 CONTINUE 40 0 CONTINUE 10 50 RUN=100 50 2 OMT( " 30(1X,F3.2))) ", FORMAT((" 12 CONTINUE 20 3 OMT" ",20F5.0) FORMAT(" 13 30 CONTINUE 30 RT(,3 (TOPOG(I,J),J=41,60) WRITE(6,13) (TOPOG(I,J),J=1,20) WRITE(6,13) RUN=141 TOPMAX=TOPO(1) RT(,2 (SLOPE(I,J),J=1,60) WRITE(6,12) 1=1,56 200 DO RT(,3 (TOPOG(I,J),J=21,40) WRITE(6,13) DO 40 K-1,9,2 40 DO SLOPE THE CALCULATE CALCULATE THE MAXIMUM ELEVATION DIFFERENCE WITHIN DIFFERENCE ELEVATION MAXIMUM THE CALCULATE O 300.1=1,56 DO END LP(,)(OMXRN* .3048 SLOPE(I,J)=(TOPMAX/RUN)* 40 TO GO 30K=1,9 DO STOP FTPA .E TP() G O 50 TO GO .NE. TOPO(K)) IF(TOPMAX TOPMAX=TOPO(K) .GT. TOPMAX) IF(TOPO(K) INTERPOLATION SCAN INTERPOLATION Program SLOPE was written speciffically for a for speciffically written was SLOPE Program

103

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104 105

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Hamblin, U.U. K., and Best, M. G., 1975, The geologic boundary between the Colorado plateau and the basin and range province (abstract): Geol. Soc. America, Abstracts with Programs, v. 7, no. 7 p. 1097.

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______, 1971b, Stream networks by headward growth and branching: Geog. Analysis, v. 3, p. 29-50.

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