Magnetostratigraphy of the 

San Francisco Volcanic Field, Arizona 
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Magnetostratigraphy of the 

San Francisco Volcanic Field, Arizona 

By K.L. TANAKA, T.C. ONSTOTT, and E.M. SHOEMAKER 

Polarity-chronostratigraphic data that document the detailed 

eruptive history of upper Cenozoic volcanic rocks in the 

San Francisco Mountain area of the southern Colorado Plateau 

U.S. GEOLOGICAL SURVEY BULLETIN 1929 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1990 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Ubrary of Congress Cataloging-In-Publication Data 

Tanaka, Kennethl. 

Magnetostratigraphy of the San Francisco volcanic field, Arizona I by KL. 

Tanaka, T.C. Onstott, and E.M. Shoemaker. 

p. em.- (U.S. Geological Survey bulletin; 1929) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1929 

1. Paleomagnetism-Arizona-Flagstaff region. 2. Geology, Stratigraphic-Cenozoic. 3. Volcanism-Arizona-Flagstaff region. I. Onstott, T.C. 

{Tullis Cullen) II. Shoemaker, Eugene Merle, 1928- . Ill. Title. IV. Series. 

QE75.B9 no. 1929 557.3 s-dc20 90-2914 

[QE501.4.P35) [538'.78791'33) CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Previous investigations 2 

Geologic setting 2 

Acknowledgments 3 

Paleomagnetic sampling and laboratory methods 3 

Magnetic properties of the volcanic rocks 6 

Polarity chronostratigraphy 7 

Determination of polarity chronozones 7 

Pre-Matuyama Chronozone 9 

Silicic and intermediate rocks 9 

Basaltic rocks 9 

Matuyama Chronozone 10 

Silicic and intermediate rocks 10 

Basaltic rocks 10 

Brunhes Chronozone U 

Silicic and intermediate rocks U 

Basaltic rocks U 

Virtual geomagnetic pole positions 12 

Migration of volcanism 12 

Conclusions 13 

References cited 13 

FIGURES 

1. Map showing late Cenozoic volcanic fields in Arizona and New Mexico 2 

2. Map showing outlines of detailed geologic maps and site-location grid system of 

samples of San Francisco volcanic field, Arizona 4 

3. Map showing major features of San Francisco volcanic field S 

4. Hemispherical plots showing average paleomagnetic vectors of sample sites 

having pre-Matuyama, Matuyama, and Brunhes ages in San Francisco volcanic 

field 6 

5. Correlation of polarity chronologie units in San Francisco volcanic field 7 

TABLES 

1. Correlation of map symbols of Wolfe and others (1987) with epochs and 

polarity chrons for basaltic units in the San Francisco volcanic field 9 

2. Mean remanent magnetic directions and virtual geomagnetic pole positions of 

polarity chronozones in the San Francisco volcanic field sites 12 

3. Rotation and flattening statistics of virtual geomagnetic pole positions of the 

San Francisco volcanic field 12 

4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the 

San Francisco volcanic field 1S 

• 

Contents Ill 
• 
Magnetostratigraphy of the 

San Francisco Volcanic Field, Arizona 

By K.L. Tanaka, T.C. Onstott,1 and E.M. Shoemaker 

Abstract 

We present remanent magnetizations determined for 

657 sites of volcanic rocks in the San Francisco volcanic field, 

an area of about 4,800 km2 in the southern part of the 

Colorado Plateau. The field includes scattered basaltic cinder 

cones and flows as well as silicic and intermediate rocks 

mostly in voluminous eruptive centers. About 90 percent of 

the sites yielded clear polarity determinations; the remainder 

have scattered data (a95 > 40°) or peculiar directions. Comprehensive stratigraphic controls-paleomagnetic polarity 

data, K-Ar and other absolute-age determinations, superposition relations, and lithologic associations-and state of 

preservation of the cinder cones provide a basis for age 

assignments of 503 separate eruptions related to basaltic 

vents and flows and 80 silicic to intermediate domes, flows, 

and flow sequences. The eruptions are assigned to three 

magnetopolarity sequences (polarity chronozones): the preMatuyama Chronozone (about 5.0 to 2.48 Ma), the Matuyama Reversed-Polarity Chronozone (2.48 to 0.73 Ma), and the 

Brunhes Normal-Polarity Chronozone (0.73 Ma to present). 

This stratigraphy documents a progression of volcanism, first 

to the northeast and then to the east: volcanic activity was 

centered along the Mesa Butte fault zone during preMatuyama and early Matuyama time and turned eastward 

through San Francisco Mountain during late Matuyama and 

Brunhes time. Site averages of magnetic vectors indicate that 

no appreciable crustal translations or rotations occurred in 

the field during eruptive activity. 

INTRODUCTION 

For several reasons, the San Francisco volcanic 

field in north-central Arizona (fig. 1) has been a region of 

considerable geologic investigation since the mid-1970's. 

First, the field is late Cenozoic in age. The most recent 

volcanic eruption occurred about 925 years ago, and the 

field may be considered to be dormant but potentially 

active (given the eruptive recurrence interval of 3,000 to 

1

Present address: Department of Geological and Geophysical 

Sciences, Princeton University, Princeton, NJ 08544. 

Manuscript approved for publication, December 20, 1989. 

4,000 yr; Wolfe and others, 1983). Second, this potential 

led to an assessment of the geothermal activity of the 

field, particularly beneath San Francisco Mountain. 

Third, many of the cinder cones in the eastern part of the 

field are late Pleistocene in age, prompting detailed 

investigations of stratigraphy and absolute age. Finally, a 

comprehensive understanding of continental volcanic 

fields requires that their chronology be thoroughly recorded, thus contributing to an integrated approach 

toward understanding the volcanic evolution. 

In 1976 the U.S. Geological Survey began a Geothermal Research Program to study this area. Most of 

our paleomagnetic investigations were conducted from 

1976 to 1980. Our primary aim was to assign all known 

volcanic materials representative of discrete eruptions 

(as interpreted from detailed geologic mapping) to a 

position in the magnetostratigraphic column that has 

been developed for the late Cenozoic. Therefore, we 

determined the magnetic vectors for most of these rocks 

and correlated the magnetic polarities with geologic 

relations and about 150 K-Ar ages. The polarity, geologic, and isotopic age data were compiled on five 1:50,000-

scale maps of the volcanic field (fig. 2): the central sheet 

(Wolfe and others, 1987a), the eastern sheet (Moore and 

Wolfe, 1987), the southwestern sheet (Newhall and others, 1987), the northwestern sheet (Wolfe and others, 

1987b ), and the SP Mountain quadrangle (Ulrich and 

Bailey, 1987). In this report, the maps are collectively 

referenced as "Wolfe and others (1987)." The K-Ar ages 

presented on these maps include many that were previously unpublished; the ages were obtained by E.H. 

McKee (U.S. Geological Survey) and P.E. Damon and 

Muhammed Shafiqullah (Laboratory of Isotope Geochemistry, University of Arizona). A preliminary magnetostratigraphy of the field was reported by Tanaka and 

others (1986). Wolfe and others (1987) also made extensive use of the paleomagnetic data in their stratigraphic 

assessment of the volcanic rocks; their maps include our 

paleomagnetic sample sites and the sites' polarities. In 

the present paper, we also provide the details of the 

paleomagnetic data and discuss assumptions, individual 

key relations, and the reliability of interpretations upon 

which the stratigraphy rests. 

Introduction 1 
Previous Investigations 

Before this research program was begun, workers 

dealt primarily with the geology and stratigraphy of the 

northern and eastern parts of the volcanic field (Robinson, 1913; Colton, 1936; Cooley, 1962; Moore and others, 1976), where erosional levels of the Little Colorado 

River valley provide a basis for stratigraphic correlations. 

Earlier paleomagnetic and radiometric studies were centered on these northern and eastern basalt flows and on 

the prominent silicic centers such as San Francisco 

Mountain, Kendrick Peak, and O'Leary Peak (Opdyke 

and Runcorn, 1956; Babbitt, 1963; Damon, 1966; Coe, 

1967; Strangway and others, 1968; Damon and others, 

1974). From this work, northeastward progression of 

volcanism along the Mesa Butte fault system (Ulrich and 

Nealey, 1976) and overall eastward migration of volcanic 

field activity (Smith and Luedke, 1984) were recognized. 

A summary of the geology and stratigraphy of the 

field, based largely on unpublished maps, K-Ar ages, and 

paleomagnetic polarities, was given by Wolfe and others 

(1983). Also on the basis of that unpublished work, 

Tanaka and others (1986) presented a comprehensive 

description of the migration and evolution of volcanism 

and determined the positions and ages of volcanic vents 

and volumes of eruptive material. They further proposed 

a model for generation of magmas by shearing at the base 

of the lithosphere, and they suggested that the eastward 

volcanic migration since Matuyama time is a product of 

westward absolute motion of the North American plate. 

Geologic Setting 

The San Francisco (SF) volcanic field in northern 

Arizona is one of several dominantly basaltic volcanic 

fields of late Cenozoic age on or near the south margin of 

the Colorado Plateau (fig. 1). The field consists of more 

than 600 Pliocene and Quaternary volcanoes and associated lava and pyroclastic flows and tephra. The volcanic 

rocks, which cover approximately 4,800 km2

, rest on 

erosional surfaces of low relief cut in Permian and 

Triassic sedimentary rocks. The volcanic field is elongate 

in plan, extending somewhat more than 100 km east -west 

and about 70 km north-south (fig. 3). 

0 150 KILOMETERS 

Figure 1. Late Cenozoic volcanic fields in Arizona and New Mexico (after Wolfe and others, 1983). Dark areas, volcanic rocks 

younger than 5 m.y.; outlined areas, volcanic rocks 5 to 16+ m.y. old. Dashed lines, approximate borders between geographic 

provinces. 

2 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
An extensive volcanic field, mostly Miocene and 

commonly referred to as the "rim basalts," lies along the 

south end of the SF volcanic field, roughly parallel with 

its long axis. Here we include the andesite dome of 

Mormon Mountain and other basaltic volcanic rocks 

surrounding it in the rim basalt field (because of their 

petrologic similarities), although Mormon Mountain was 

included in the SF volcanic field by Robinson (1913) and 

has a Pliocene age. The rim basalts are generally more 

strongly offset by normal faults and are more dissected by 

erosion than the lavas of the SF field. Most K-Ar ages 

obtained in the rim basalts range from 5 to 8 Ma (Luedke 

and Smith, 1978). The oldest volcanoes and lava flows of 

the SF volcanic field are found where they overlap the 

basalts along the southwest margin of the field; it is not 

clear whether there is a break in time between volcanism 

of the rim basalt and that of the SF field. Hence, the 

boundary of the field is ill defined on the southwest; we 

have roughly drawn it on the basis of morphology and 

petrography at the limit of detailed geologic mapping by 

Wolfe and others (1987). The relations of these rim 

basalts to the petrogenetic evolution of the SF field and 

to the deep-seated processes along the south margin of 

the Colorado Plateau remain topics for future analysis. 

Five major centers of intermediate to silicic rocks 

are located within the SF volcanic field (fig. 2). From 

west to east they are Bill Williams Mountain ( dacitic and 

andesitic domes and flows), Sitgreaves Mountain (rhyolitic domes), Kendrick Peak (andesitic to rhyolitic domes 

and flows), San Francisco Mountain (a stratovolcano 

dominantly made up of andesitic flows with dacitic and 

rhyolitic domes and flows) and O'Leary Peak ( andesitic 

to rhyolitic domes and flows). 

Several regional normal fault systems of late Cenozoic age (fig. 2) cut the Paleozoic sedimentary rocks and 

locally affect rocks of the SF field as well. These fault 

systems have been shown by Shoemaker and others 

(1978) to be related to large, ancient systems of faults 

that cut the Proterozoic crystalline basement. A major 

one, the Mesa Butte fault system, trends northeast across 

the SF volcanic field. Several silicic to intermediate 

volcanic centers, including Bill Williams Mountain, Sitgreaves Mountain, and Kendrick Peak, occur along or 

close to this fault system, which cuts some of the volcanic 

rocks (Ulrich and Nealey, 1976). The north-trending Oak 

Creek Canyon fault system cuts some cinder cones north 

of Oak Creek Canyon (Wolfe and others, 1987a). The 

north limit of this system is unknown because of burial; 

however, its projection places it beneath San Francisco 

Mountain. Minor faults of the Cataract Creek fault 

system trend northwest across the eastern part of the SF 

volcanic field. Many basaltic cinder cones, as well as 

silicic volcanoes, are aligned along exposed faults or form 

chains parallel with the faults in each system. Deepseated crustal structures clearly control the location of 

many of the volcanic vents. 

Acknowledgments 

We are grateful for the extensive assistance of 

Edward W. Wolfe and George E. Ulrich of the U.S. 

Geological Survey and Richard F. Holm of Northern 

Arizona University in matters relating to the geology of 

the volcanic field. Christopher D. Condit of the University of Massachusetts and George E. Ulrich provided 

helpful reviews of the manuscript. 

PALEOMAGNETIC SAMPLING AND 

LABORATORY METHODS 

The rocks sampled at the 657 paleomagnetic sites 

in this study include most of the mapped volcanic units of 

Wolfe and others (1987). Some of these units, particularly those from basaltic vents and lava flows, represent 

many distinct eruptions. Volcanic rocks west of and near 

San Francisco Mountain were sampled comprehensively 

because of the scarcity of other information from which 

to interpret the stratigraphy. East of San Francisco 

Mountain, paleomagnetic sampling was done by J.N. 

Kellogg (unpublished work) and Champion (1980, table 

1) to help define the chronology of the informal stratigraphy developed by Moore and others (1976). This 

stratigraphy is based on terrace levels related to downcutting in the Little Colorado River valley; it includes 

(from oldest to youngest) the Woodhouse, Tappan, Merriam, and Sunset age groups. The three youngest groups 

correlate with middle and late Brunhes time, whereas the 

Woodhouse group corresponds to early Brunhes and 

older times. 

All localities whose paleomagnetic vectors were 

analyzed in this study are listed in table 4. Virtually all 

paleomagnetic sites sampled in the SF volcanic field since 

the mid-1970's are included in table 4, which lists rock 

type, location, and paleomagnetic, stratigraphic, and KAr age data. Site locations are shown on the samplelocality maps of Wolfe and others (1987). The preface of 

table 4 gives more details on its structure and the labeling 

scheme used. 

The basic polarity chronostratigraphic unit of this 

study comprises the products of an individual eruptive 

episode (or an eruptive unit) that constructed a vent or, 

in some cases, produced only flows or tephra; flows or 

tephra effused during vent construction are considered 

part of that vent's polarity chronostratigraphic unit. Flow 

sequences, including those not sampled comprehensively, are also considered products of an individual eruptive 

episode. Thus many eruptive units consist of both vent 

and flow materials, and more than one paleomagnetic 

sample site was obtained for many of the eruptive units. 

(In table 4, additional sites for each eruptive unit are 

referred back to the first site under the heading "Field 

relations," following the phrase "Same as".) 

Paleomagnetic Sampling and Laboratory Methods 3 
We separated the rocks into (1) basaltic and (2) 

silicic and intermediate categories on the basis of their 

general difference in eruption style rather than on strictly 

lithologic and chemical distinctions. Therefore, the character of the vent (for example, cinder cone or dome) and 

the apparent viscosity of the lava flows were the primary 

criteria used to distinguish these categories. This approach is based on the organization of map units employed by Wolfe and others (1987), although most "'f 

their geologic units comprise several eruptive units. The 

basaltic rocks include basalt, basaltic andesite, andesite, 

and benmoreite. They include flows and a single tuff that 

demonstrably or presumably were effused from mapped 

or buried vents. Where the vent is known, Wolfe and 

others (1987) labeled the associated basaltic flows and 

tephra by that vent number. Where andesites and benmoreites form part of a major eruptive center consisting 

of at least several units, or where they form domal 

structures, they are included with silicic and intermediate 

rocks (which also consist of dacite, trachyte, and rhyolite). Careful reconsideration of some sites of intermediate lithology presented by Tanaka and others (1986) 

required reassignment of some sites to either a basaltic 

or a silicic category. These changes, however, do not 

appreciably affect the results. 

112°30' 112°15' 112°()()' 

T R1W 28N 

54 __ 55--

43 __ 44-- 45--

32-- 33 __ 34-- 35--

sw 

22-- 23-- 24-- 25--

12-- 13-- 14-- 15 __ 

R2W 35°00' 

For silicic and intermediate rocks, 92 sites representing 80 different domes, tephra, flows, and flow sequences were sampled, including a thick section of 

layered andesite and dacite flows on San Francisco 

Mountain that was sampled in detail. Babbitt (1963) had 

determined the polarity of a few of these units and of the 

dacite of O'Leary Peak, which we did not sample. 

The 565 sample sites of basaltic vents and lava 

flows represent 503 separate eruptions. The eruptions 

include 32 lava flows, 1 tuff from buried or unknown 

vents, and 2 flows from local fissures. A few other flows 

were not sampled, particularly those whose stratigraphic 

positions had already been determined by known field 

relations. J.N. Kellogg (unpub. data, 1976) sampled 13 

sites east of San Francisco Mountain on younger Woodhouse lava flows to distinguish rocks of Brunhes age from 

those of Matuyama age. Champion (1980, table 1) measured magnetic vectors of 11 sites of Merriam- and 

Sunset-age vents and lava flows to determine absolute 

ages according to the secular variation of the Earth's 

magnetic dipole position for the past few thousand years. 

Kellogg's and Champion's data are included in table 4. 

We obtained oriented core samples, mostly by 

using a portable rock drill similar to that described by 

Doell and Cox {1965). Because of logistic difficulties for 

111°45' 111°30' 111°15' 111°00' 

R13E 

71-- 8 T 

61-- 26 

SP AREA OF MAP N 

T 

56 -- 57 __ 25 

N 

46 __ 49--

36:..._ 37-- 39-- 30--

c E 

26-- 27 __ 29-- 20--

16--

I 

I 

0 5 10 MILES 

I I 

I I I 

0 5 10 T 

19 

N 

Figure 2. Outlines of detailed geologic maps of San Francisco volcanic field, Arizona (heavy lines; Wolfe and others, 1987), 

and site-location grid system for samples listed in table 4. Boxes show township and range squares identified by grid 

notations (explained in table 4 preface). Maps of San Francisco volcanic field identified by letters: C, central; E, east; NW, 

northwest; SW, southwest. SP, SP Mountain. 

4 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
a few sites high up on Kendrick Peak and San Francisco 

Mountain, some samples were collected as oriented 

blocks that were taken from outcrops and drilled in the 

laboratory. Usually six to eight samples (cores or blocks) 

were taken per site, but as many as 24 samples were 

taken from outcrops where well-defined magnetic vectors were desired. Generally, the samples were taken tens 

of centimeters to meters apart along one or more nearby 

outcrops. For a few sites (in particular for broad flows), 

samples were taken tens of meters to 100 m apart. 

Sample azimuths were measured by a sun compass when 

possible, and all samples were oriented by a magnetic 

compass. Because lightning has extensively remagnetized 

the volcanic rocks, we sampled oxidized vent rocks rather 

than lava flows where possible, as discussed below. 

Appreciable rotations have occurred in the tops and 

flanks of some blocky flows and domes, which are mostly 

intermediate to silicic in composition. We could sample 

some vents only from large cinder bombs protruding 

through loose cinders. If samples from scoria bombs 

yielded discordant data, we assumed that the samples 

represent ~lumped or rotated material, and therefore we 

discarded them. 

112°30' 112°15' 112°00' 

R2W 

35°45' 

8 

AREA OF MAP 

35°30' 

35° 15' 

35•oo· 

Because most of the rocks we sampled are strongly 

magnetized, we made measurements using either (1) a 

high-rpm, air-driven, spinner magnetometer on 2.5-cmdiameter, recored samples generally weighing 15 to 25 g 

or (2) a superconducting magnetometer for ·wafershaped samples 2.5 em in diameter and 3 to 7 mm thick, 

mostly weighing 3 to 8 g. Even so, some of the basalt 

samples had natural remanent magnetization (NRM) 

intensities beyond the range of the instrument, especially 

samples suspected of having a lightning-induced, isothermal remanent magnetization (IRM) component. For 

cross-checking, we measured some samples with both 

instruments. For this purpose, we took more than one 

sample from some of the cores; however, we. report only 

the measurements of one sample per core. All samples 

were subjected to alternating field ( AF) demagnetization 

on either of two tumbling AF demagnetizers. Generally, 

samples were step-wise demagnetized at intervals of 250 

oersteds to a maximum of 1,000 oersteds, on the basis of 

the step in which optimal cleaning of the IRM component occurred. For 21 sites, we present NRM data 

because of optimal statistics at this step or because 

samples were lost following NRM measurements; fortu111°45' 111°30' 111°15' 

Figure 3. San Francisco volcanic field, Arizona (after Tanaka and others, 1986). Gray pattern, Pliocene and Pleistocene 

volcanic rocks; silicic centers within volcanic field are white. Numbers in parentheses indicate ages in millions of years. Faults 

dotted where concealed; bar and ball on downthrown side. 

Paleomagnetic Sampling and Laboratory Methods 5 
nately, however, the statistics on the latter samples are 

adequate. Onstott, who worked mainly on the sites in the 

SP Mountain quadrangle, used mostly demagnetization 

intervals of 170, 270, 330, 500, 660, and 750 oersteds. 

A 

w 

B 

w 

c 

w 

N 

+ + .... + 

+ .f + + 

+; tt+~A + + -~+1+ .. +; + + + + 

+ +* + 

+ +-f:t.:t 

+ 0 

0 

8 0 & ~0 0 0 

0 0 0 0 0~0 0 0 ocf'o o Cillo oo ~ 

o 8o 0 q] cP ~oo c9 ~o ct>o8 

0 0 

s 

N 

* 

+" ... 

+ +#++ + 

+ + + ++ 

+ 

+o 0 0 0 

o 8o o o ~o:§P o 

0 

oo o~~ Oo o~go o o~Cib 0 o 0 10 o 

OCD~~ 0~1' 0 0 0 0 

o 10 o oo 

0 cP ~ %0 

o 't ~ oo 

0 0 0 0 

0 

s 

N 

s 

E 

0 

E 

E 

Samples that probably retain a large component of 

IRM, as indicated by either high magnetic intensity or 

large deviation of direction from the majority of directions at a given sample site, were not included in calculations of the average direction of magnetization. This 

selection process did not alter polarity determinations; 

however, data from about 15 sample sites were insufficiently coherent to determine a polarity and were discarded. Also, the magnetic vectors of 66 sites were of 

poor precision ( a95 > 40°) or peculiar direction, even 

following several demagnetization steps. (Reasons for 

poor data are discussed in the following section.) The 

polarities of these sites are queried in table 4, and their 

paleomagnetic data are omitted. Samples taken by J.N. 

Kellogg (unpub. data, 1976) and D.E. Champion (1980, 

table 1; written commun., 1983) were acquired and 

measured by those workers using the methods described 

above. All measurements were performed at the U.S. 

Geological Survey in Flagstaff, Ariz., except those by 

Champion, which were performed at the U.S. Geological 

Survey in Menlo Park, Calif. The average magnetic 

vectors for all sites that have reliable data in table 4 are 

plotted by polarity chronozone in figure 4; polarities of 

the rocks at eruptive sites are shown in Tanaka and 

others (1986, figs. 4, 5). 

MAGNETIC PROPERTIES OF 

THE VOLCANIC ROCKS 

Paleointensity studies of the Earth's magnetic field 

that are based on volcanic rocks in the SF volcanic field 

(Babbitt, 1963; Coe, 1967; Strangway and others, 1968) 

have shown that the major magnetic component in the 

basaltic lava flows is borne by titanomagnetite. This 

mineral has a Curie point between 400 and 550 °C, 

depending on the relative abundances of iron and titanium. All of the volcanic rocks studied (except perhaps for 

the tops of some silicic and intermediate flows and 

domes) apparently came to rest at sufficiently high 

temperatures for their thermal remanent magnetization 

(TRM) to be acquired in place. 

The sampled basaltic lavas general1y have NRM 

intensities of 10-3 to 1 gauss/cm3

, made up of TRM and 

IRM components. The intensities of the individual components depend on sample mineralogy and proximity to 

lightning strikes. Despite our efforts to avoid anomalous 

Figure 4. Hemispherical equal-area plots of average paleomagnetic vectors of sample sites in San Francisco volcanic 

field, Arizona. Pluses, positive inclination. A, Sites of preMatuyama age. Circles, negative or zero inclination. 8, Sites 

of Matuyama age. Circles, negative inclination. C, Sites of 

Brunhes age. Circle, zero inclination. 

6 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
magnetism resulting from lightning strikes, the NRM's of 

most samples taken from lava flows are high in intensity 

and are dominated by an IRM component. Most samples 

taken from road cuts, cinder pits, and oxidized vent 

material have low NRM intensities and only minor IRM 

overprints. The magnetization of the vent material is 

dominated by hematite. The coercivity of hematite is 

sufficiently high that the vent materials are relatively free 

of IRM, despite their increased exposure to lightning on 

the rims of cinder cones. 

Thus oxidized vent materials commonly showed a 

tight grouping of NRM vectors (resulting in a95 < 5-7° 

and "> 100), and the vector mean generally changed only 

a few degrees upon demagnetization. Where other magnetic components apparently caused greater scattering of 

NRM vectors (particularly for magnetite-dominated 

samples), demagnetization commonly altered the site 

mean by more than 10°, and clustering of the vectors 

increased dramatically. On the other hand, nearly 10 

percent of all sites retained a high degree of their 

secondary remagnetizations (to the limit of our demagnetization capability). 

POLARITY CHRONOSTRATIGRAPHY 

Several stratigraphic systems of units have been 

used to define the ages of volcanic rocks in the SF field 

(fig. 5). In our study, we make particular application of 

the polarity reversal record for the past 5 m.y. The 

fundamental polarity-chronostratigraphic unit, called the 

"polarity chronozone," consists of rocks of a particular 

age as defined by a given polarity signature. The equivalent chronologie time span is the "polarity chron." 

Determination of Polarity Chronozones 

On the basis of polarity data, radiometric ages, and 

stratigraphic relations, we assigned mapped volcanic 

units (which may include deposits of more than one 

eruption) to polarity chronozones. The polarity chronozones for the past 5 m.y. were defined by Mankinen and 

Dalrymple (1979) on the basis of statistical analysis of 

K-Ar ages and of magnetic polarity determinations that 

meet strict requirements of precision. The Brunhes Normal-, Matuyama Reversed-, Gauss Normal-, and Gilbert 

Reversed-Polarity Chronozones defined originally by 

Cox and others (1964) are the principal units for which 

magnetostratigraphic correlations within the volcanic 

field have been attempted. Although normal-polarity 

subchronozones of the Matuyama, such as the Reunion 

Normal-Polarity Subchronozone (2.14 to 2.12 and 2.04 to 

2.01 Ma), Olduvai Normal-Polarity Subchronozone (1.87 

to 1.67 Ma), and Jaramillo Normal-Polarity Subchronozone (0.97 to 0.90 Ma), are represented in the field (for 

example, by sites 3611, 4003, 6803A, and 6804 ), sufficient K-Ar and stratigraphic controls were not available 

in most cases for us to identify consistently the volcanic 

units belonging to these polarity subchronozones (fig. 5). 

Thus normal-polarity sites of Matuyama age, for example, are not categorized by polarity subchronozone in 

table 4. Age control was also insufficient for consistent 

distinction between rocks of Gauss and Gilbert ages 

(about 5.0 to 2.48 Ma). We therefore grouped rocks 

belonging to these polarity chronozones with a few older 

rocks and considered their age to be "pre-Matuyama" 

(fig. 5). 

Age Period Epoch Informal Polarity 

(Ma) age group chron 

~ Qj Q) 

0.0- - = u • fiJ 

0 

r~ ~ 0 

:I: 

-

0.2-

fiJ 

Q) 

s:. 

c 

0.4- 2 c Ill liS 

Q. 

Q. 

> CIS 

a: Q) 1- - < c z Q) 

a: u 

w .s 1- fiJ 

0.6- < a; ::::) ii: II 0 1: 

II - 1: 

? Q) 

fiJ 

0.8 ;, 

0 

s:. 

, 

0 

0 liS 

;: 

11 

E - liS 

>-

;, 

a; ., :E 

1.0-

~ ~ ~ 

«i 

T ~l~ - - - oc 

-~J ;, 

'Q) 

a: liS 3.0- > Q) E a: c fiJ liS 

< Q) fiJ >- i= u ;_, ;, 

a: .!2 (!) a;. - w ii: :E 1-

~J I 

Q) 

0:: 

5.0- - - c; 

Figure 5. Correlation of polarity chronologie units used in 

San Francisco volcanic field, Arizona. Informal age groups 

based on stratigraphy of lava flows in Little Colorado River 

valley (Moore and others, 1976). Polarity chrons show periods of normal polarity (solid) and reversed polarity (open); 

•pre-Matuyama• is informal name for Gauss Normal- and 

Gilbert Reversed-Polarity Chrons combined. Figure modified 

from correlation chart of Moore and Wolfe (1987); reversal 

record from Mankinen and Dalrymple (1979). 

Polarity Chronostratigraphy 7 
Most of the K-Ar ages cited in this study were 

determined by P.E. Damon and Muhammed Shaffiqullah (Laboratory of Isotope Geochemistry, University of 

Arizona) and E.H. McKee (U.S. Geological Survey) and 

were published on the maps of Wolfe and others (1987). 

Ages obtained prior to 1979 were slightly revised to 

reflect new decay constants (Dalrymple, 1979). A few 

absolute ages were also obtained by secular variation 

studies (Champion, 1980, table 1; written commun., 

1985), by 14C dating (S.W. Robinson, written commun., 

1983), by fission tracks (C.W. Naesar and GA. Izett, 

written commun., 1975), and by dendrochronology (Smiley, 1958); these ages generally apply to young Brunhes 

rocks. Absolute ages that pertain to paleomagnetic sites 

used in this study are given in table 4. Units dated by 

K-Ar methods were assigned to a single polarity chron if 

the one-standard-deviation interval includes only that 

polarity chron (these units include Brunhes basaltic rocks 

categorized as "Dated by field relations" in table 4 ); 

otherwise, geomorphic or contact relations of the given 

unit with one or more dated units were used to ascertain 

the polarity chronozone. 

In addition to paleomagnetic data and absolute 

ages, we used broad and local stratigraphic designations, 

superposition relations, lithologic correlations, and geomorphic preservation as detailed by Wolfe and others 

(1987) to ascertain local volcanic stratigraphy. These 

methods and some of the general relations are described 

below. 

Fresh cinder cones and rough-surfaced lava flows 

in the eastern part of the field are clearly younger than 

the eroded vents with exposed feeder dikes and the 

smooth-topped flows in the western areas. Near the 

Little Colorado River (fig. 3), rates of downcutting have 

been rapid enough to enable distinction of younger flows 

in stream bottoms from older flows at successively higher 

terrace levels above present drainage. These relations 

enabled a relative-age classification by Colton (1936) and 

Cooley (1962) and, more recently, a stratigraphy for the 

eastern part of the volcanic field by Moore and others 

(1976). Radiometric ages indicate that lavas and tephra 

of the Tappan, Merriam, and Sunset basaltic stages of 

Moore and others (1976) are part of the Brunhes Normal-Polarity Chronozone (fig. 5). On the basis of magnetic polarity and K-Ar ages, lavas dated as Woodhouse 

age by these workers commonly can be shown to belong 

to the Matuyama or the older part of the Brunhes. 

In the eastern part of the volcanic field, all volcanic 

vents or flows suspected of being pre-Brunhes in age 

were studied for paleomagnetic polarity, and most were 

analyzed radiometrically; most units known to be of 

Brunhes age on the basis of stratigraphic position were 

not sampled. In a few cases, K-Ar ages are inconsistent 

with polarity and other stratigraphic indicators; following 

the lead of Wolfe and others (1987), we discarded these 

ages. 

In the central and western parts of the volcanic 

field, we made extensive use of superposition relations 

(chiefly of flows) in deciphering the magnetostratigraphy. 

When superposition relations are combined with radiometric ages and paleomagnetic polarity data, polarity 

chron determinations can be made for most vents. We 

correlated some vents on the basis of similar lithology 

and proximity to vents of known age. Cinder cones having 

the same rock type are commonly in clusters or linear 

patterns and can be interpreted as the products of a 

single eruptive episode. For example, Sunset Crater and 

an associated group of vents along a northwest trend 

probably all erupted within a period of200 years (Champion, 1980, p. 50). Silicic centers, on the other hand, have 

eruptive histories spanning about 1 m.y. (Damon and 

others, 1974). 

We made polarity-chronostratigraphic assignments 

for all eruptive units represented by basaltic vents, for 

most of the lava flows, and for most intermediate to silicic 

volcanic units. Some basaltic rocks having stratigraphic 

positions near polarity chronozone boundaries cannot be 

placed with certainty into a polarity chronozone. We infer 

the probable assignment of such rocks, as shown by their 

placement in a polarity chronozone in table 4, and we 

also indicate alternative possibilities (for example, a 

group of sites in the Matuyama category is headed 

"Matuyama or pre-Matuyama"). Synoptic views of our 

inferred polarity chrons (except for a few sites that we 

later changed) are shown in figures 6 and 7 of Tanaka 

and others (1986). 

Because the sampling was so comprehensive, our 

polarity data were significant in determining the stratigraphic ages of basaltic units mapped by Wolfe and 

others (1987). Many sample sites, in fact, were selected 

because they bear on local stratigraphic problems. As a 

result, the map symbols of Wolfe and others are largely 

based on those of pre-Matuyama, Matuyama, and Brunhes Chronozones. The relations between most of the map 

symbols for basaltic rocks and our polarity-chron designations are summarized in table 1. 

The geologic maps (Wolfe and others, 1987) also 

provide an index to the vent-numbering system used for 

the field; they show the locations of the geologic units, 

K-Ar dated sites, and polarity sample sites; they present 

the correlation of map units; and they indicate detailed 

superposition relations. This information is essential to 

the following detailed discussion of the stratigraphy, and 

the reader will need to refer to the maps to locate specific 

rock units and verify stratigraphic inferences. Because 

the correlation charts for the maps contain much of the 

general stratigraphic information, our discussion focuses 

on detai1ed relations among rocks of individual eruptive 

episodes. This work was complex, not only because some 

individually mapped units (particularly many of the silicic 

to intermediate flow units) may be composites of rocks 

produced over several eruptive episodes, but also be8 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
Table 1. Correlation of map symbols of Wolfe and others 

(1987) with epochs and polarity chrons for basaltic units in 

the San Francisco volcanic field, Arizona 

[Symbol is only the first one, two, or three letters of many map 

symbols used by Wolfe and others (1987)] 

Symbol Epoch(s) Polarity chron(s) 

Qbs Holocene (Sunset1

) Latest Brunhes 

Qby Latest Pleistocene Later Brunhes 

Qb Middle Pleistocene Early Brunhes 

Qbm Early or middle Late Matuyama or early 

Pleistocene Brunhes 

Om Early Pleistocene Late Matuyama 

QTm Late Pliocene, early Matuyama 

Pleistocene 

QT Pliocene or Pleistocene Pre-Matuyama or 

Matuyama 

T Miocene and Pliocene Pre-Matuyama, 

undivided 

Tm Late Pliocene Early Matuyama 

Ty Most of Pliocene Gilbert or Gauss 

To Miocene Pre-Gilbert 

1

Informal age of Wolfe and others (1987) 

cause many single eruptive episodes produced several 

mapped units (vent, flow, or tephra deposits). In the 

following discussion, site numbers (for example, 1232A) 

are independent of vent numbers. A given eruptive unit 

was commonly sampled at more than one site. 

Pre-Matuyama Chronozone 

Rocks of this informally named zone are mainly of 

the Gauss Normal- and Gilbert Reversed-Polarity Chronozones (about 5.0 to 2.48 m.y. old). Most of those in the 

San Francisco volcanic field are located in the western 

end. Most basalts older than 5 m.y. in the central and 

southern parts of the volcanic field are considered to be 

part of the rim basalts, and only a few sites in these rocks 

were sampled. There are comprehensive K-Ar ages for 

silicic volcanic units but few for basalts considered to be 

in this polarity zone. 

Silicic and Intermediate Rocks 

The silicic and intermediate rock sites of preMatuyama age consist primarily of the Bill Williams 

Mountain dome complex, nearby domes to the south and 

east, and the eastern part of the Sitgreaves Mountain 

dome complex and rhyolite domes east of it. The rocks of 

Bill Williams Mountain are dominantly dacitic, most 

have normal polarity, and the K-Ar ages for them range 

from 5.03±0.50 to 2.85±0.91 Ma. The dacite of Hell 

Canyon (site 1232A, 5.15±0.17 Ma) also is preMatuyama in age. Two sites of Sitgreaves Mountain 

rocks have ages of 2.85±0.06 and 2.84±0.02 ·Ma and 

normal polarity. Pre-Matuyama rhyolite domes east of 

the mountain have ages and polarities of 2.88±0.09 Ma 

(normal), 2.79±0.07 Ma (reversed), and 2.74±0.16 Ma 

(reversed). A dome north of Sugarloaf Mountain (unsampled, 2.78±0.13 Ma; informally named "North Sugarloaf Mountain" by Wolfe and others, 1987a; see fig. 3), 

the only pre-Matuyama silicic unit in the eastern part of 

the volcanic field, has no polarity determination. 

Basaltic Rocks 

Rim basalts and basaltic andesites in the area 

(units Tob, Toab, Tocb, and older materials of unit Tb as 

mapped by Wolfe and others, 1987) have K-Ar ages of 

6.38±0.32 to 5.62±0.19 Ma and are exposed in the 

vicinity of Flagstaff (site 1710), in the southern part ofthe 

map area (vents 0626, 1110 1222, 1232, 2135, and 

2136A), and at Cedar Ranch Mesa (vent 4609) on the 

north edge of the field. Although their extent is obscured 

by younger lavas, sparse exposures suggest that the rim 

basalts make up only a minor part of the volume of lavas 

in the map area. Because the rim basalts have similar 

ages and distinct petrographic affinities, they may represent an episode of volcanism genetically distinct from the 

one that produced the highly varied lavas of the SF 

volcanic field (Wolfe and others, 1987a). 

The largest concentration of pre-Matuyama basaltic vents occupies the western part of the field northwest 

of Bill Williams Mountain. Most of the identified vents 

are in T. 22 and 23 N., R. 1 W. and 1 E. (Site and vent 

numbers start with 2Z, 3Z, 21, and 31; Z indicates R. 1 

W.; see figure 2.) As a group, these vents overlie the rim 

basalts and appear more degraded than vents to the east; 

most of them have reversed polarity. Some of the vents 

underlie rocks of probable Gauss age (in particular, the 

flows of vents 2220 and 2222; see below). On this basis, 

Newhall and others (1987) assigned these vents and their 

flows to the pre-Matuyama Chronozone (their unit Tb). 

Most of the pre-Matuyama rocks in the southern 

and western parts of the field were assigned to basalt of 

Pliocene age (map unit symbols beginning with Ty, 5.0 to 

2.48 Ma). This group of basalts includes (1) rocks having 

K-Ar ages within this time period (materials of vents 

1211, 1233, 2519B, and 6806 and flow 2233A); (2) the 

basalt flows of Volunteer Mountain (unit Tyvb), which 

have reversed polarity, are similar in composition to 

rocks about 4 m.y. old in Volunteer Canyon in the 

south-central part of the field (E.W. Wolfe, written 

commun., 1986), and overlie rim basalts; (3) materials of 

10 vents (9 having normal polarity) mostly south of and 

predating the andesite flow of Howard Mesa (2.06±0.18 

Polarity Chronostratigraphy 9 
Ma); (4) rocks of a group of six deeply eroded vents 

aligned in a northwest trend, northwest of Howard Mesa, 

having mostly normal polarity (probably Gauss in age); 

(5) normal-polarity materials of vents 2220 and 2222, 

which are younger than andesite dome 2222A 

(3.48±0.05 Ma), and materials of other nearby vents of 

mostly normal polarity that underlie reversed-polarity, 

Matuyama rocks to the east; and ( 6) assorted other vent 

materials related stratigraphically, areally, magnetically, 

and compositionally to the first five groups. Overlying the 

several types of Tertiary units described above are 11 

vents that are probably of pre-Matuyama age but which 

might be of Matuyama age. 

Matuyama Chronozone 

The Matuyama Chronozone, having dominantly 

reversed polarity, spans the period between 2.48 and 0.73 

Ma. The Reunion, Olduvai, and Jaramillo Normal-Polarity Subchrons account for about 0.32 m.y., or 18 

percent of the chron (fig. 5). Units of Matuyama age are 

found over most of the San Francisco volcanic field; the 

greatest concentration is in the west half. 

Silicic and Intermediate Rocks 

Most of the silicic and intermediate rocks of the 

Matuyama Chronozone lie along the northeast-trending 

Mesa Butte fault, northeast of pre-Matuyama silicic 

rocks. These Matuyama rocks include (1) the silicic 

domes on Sitgreaves Mountain (2.26±0.10 and 

1.90±0.12 Ma), (2) all rock units on Kendrick Peak 

(2.37±0.21 to 1.35±0.05 Ma) except for one dome 

(unsampled, 2.70±0.05 Ma), (3) four isolated rhyolite 

domes east of Sitgreaves Mountain and Kendrick Peak 

(2.15±0.13 to 1.29±0.23 Ma), the youngest of which is a 

plug in a benmoreite dome; ( 4) the andesite flow of 

Howard Mesa (2.06±0.18 Ma), (5) the Slate Mountain 

domes (1.90±0.35 and 1.54±0.02 Ma), (6) the trachyte 

flow of Bull Basin Mesa (1.14±0.17 Ma), and (7) the 

andesite flows of Moritz Ridge (site 3401A). All but 

three of the sites yielded reversed polarity, some of which 

is questionable. Within San Francisco Mountain, several 

units have K-Ar ages of less than 1.0 Ma that place them 

in the late Matuyama, and an early rhyolite dome has an 

age of 1.82±0.16 Ma; these units were not sampled for 

magnetic polarity. 

Basaltic Rocks 

Most Matuyama vents are exposed, but several 

probably underlie younger rocks of and near San Francisco Mountain. Many of the Matuyama cinder cones are 

clustered and elongated along northwest, north, and 

northeast trends, reflecting local structures. 

For Matuyama basaltic rocks, 19 erupted deposits 

have been dated by K-Ar and measured paleomagnetically. Most rocks of these dated eruptions are in two 

groups. The first group consists of vent materials and 

flows of the SP Mountain quadrangle and the eastern 

sheet, most of which are well defined stratigraphically 

from overlap relations and erosional terrace levels. Although dominantly reversed, a few apparently were emplaced during normal-polarity subchrons of the 

Matuyama. Of this first group, the deposits of 10 eruptions have K-Ar ages in the range of 1.38±0.16 to 

0.83±0.04 Ma; 3 of these 10 have normal polarity and 

range in age from 1.04±0.14 to 0.85±0.12 Ma (vent 6736 

and flows of sites 4003 and 6803A). The ranges of 

uncertainties in their ages indicate that these normalpolarity rocks formed during the Jaramillo NormalPolarity Subchron (0.97 to 0.90 Ma). Other probable 

Jaramillo flows (sites 5033 and 5932) also have normal 

polarity, formed during the Woodhouse basaltic stage, 

and are older than rocks dated as 0.49±0.11 and 

0.80±0.11 Ma, respectively. Some of the vents and flows 

in the Little Colorado River valley do not have K-Ar ages 

but have been placed in the Woodhouse age group 

(Moore and others, 1976); they have reversed polarity 

and thus are assigned a Matuyama age. The second 

group of dated Matuyama rocks consists of benmoreites 

that crop out along and near the Oak Creek Canyon fault 

(vents 0603, 0610, 0611, 0611A, 0614, 0615, 1622, and 

1628) and south of Kendrick Peak (vents 2506 and 

3509A, domes 2530, 3423A, and 3435, and a flow sampled at site 2629). Although only the vents are grouped 

with the basaltic rocks, all the domes and the flow are 

dated, and their ages are consistent with those of the 

vents. All these sites have reversed polarity; seven K-Ar 

ages determined for them range from 1.61±0.05 Ma 

(dacite plug of vent 0603) to 0.95±08 Ma. Some units 

having no K-Ar ages have stratigraphic positions consistent with these ages. 

Most of the remaining basaltic rocks (largely not 

analyzed radiometrically) assigned to the Matuyama 

Chronozone belong to one of two groups. In the first 

group are vents, dominantly of reversed polarity, that 

overlie pre-Matuyama basalts in a stratigraphic position 

similar to that of the andesite of Howard Mesa 

(2.06±0.18 Ma) and vent 3335 (1.07±0.06 Ma). These 

vents have township and range prefix codes 31, 32, 33, 42, 

and 43. In the second group are vents and flows, mostly 

of reversed polarity, in the central part of the field 

surrounding the silicic centers of Kendrick Peak, Sitgreaves Mountain, and Slate Mountain and extending to 

the north and south borders of the mapped area. A 

Matuyama age is indicated for four of these vents (2405, 

2416, 2519, and 3433) that have reversed polarity and 

K-Ar ages of 2.46±0.11 to 0.69±0.13 Ma and for other 

10 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
vents and flows that have diagnostic stratigraphic relations with other rocks. Examples of stratigraphic relations that indicate age are vents 4507, 4508, and 4517 that 

overlie the trachyte flow of Bull Basin Mesa, which has a 

K-Ar age of 1.14±0.17 Ma. The township and range 

codes (see figure 2) for this group of rocks are 14, 15, 16, 

23, 24, 25, 26, 34, 35, 44, 45, 53, 54, 55, 64, 66, and 74. 

Four vents having normal polarity occur in areas of 

clearly defined Matuyama rocks. However, evidence is 

insufficient for us to be certain if they belong to the 

normal-polarity subchronozones of the Matuyama or to 

the Brunhes Chronozone. 

Brunhes Chronozone 

All eruptive vents and centers of Brunhes age in 

the San Francisco volcanic field are east of long 112°. 

They have several characteristics: high stratigraphic position (in the informal Tappan, Merriam, and Sunset 

basaltic stages), recent K-Ar ages, low degree of erosion, 

and exclusively normal polarity (Mankinen and Dalrymple, 1979). 

Silicic and Intermediate Rocks 

Silicic to intermediate units in the Brunhes Chronozone include most of the complex at San Francisco 

Mountain (most ages are 1.0 to 0.4 Ma), materials of 

O'Leary Peak (about 0.2 Ma), and the rhyolite of White 

Horse Hills. All 20 paleomagnetic sites on San Francisco 

Mountain have yielded normal polarity, including a stratigraphic section in Dunham Canyon (site 3729) of andesite and dacite flows having K-Ar ages of 0.75±0.07 Ma 

(at base of section) and 0.43±0.03 Ma (at top of section). 

As previously mentioned, some San Francisco Mountain 

rocks of late Matuyama age (based on K-Ar ages) were 

not sampled paleomagnetically. 

O'Leary Peak is .~omposed mainly of dacite and 

some rhyolite and andesite that have K-Ar ages of 

0.25±0.04 to 0.17±0.04 Ma and normal polarity (Babbitt, 1963). The rhyolite of White Horse Hills uplifted 

andesites of San Francisco Mountain that are about 0.4 

m.y. old, and its age has therefore been interpreted as 

Brunhes (Wolfe and others, 1987a). 

Basaltic Rocks 

Most of the sampled vents of Brunhes age are 

immediately north and west of San Francisco Mountain. 

More than 240 eruptions represented by vents and flows 

have been designated Brunhes in age (Wolfe and others, 

1987). Of these deposits, 126 have been sampled; most of 

the remainder are east of San Francisco Mountain. 

As noted above, some vents of normal polarity in 

the eastern part of the area having Brunhes rocks have 

equivocal stratigraphic positions that may place some of 

them in normal-polarity subchronozones of the Matuyama. For this reason, we provisionally designated 34 sites 

as Brunhes and categorized them as "Brunhes or 

Matuyama" in table 4. However, placement of the remaining normal-polarity rocks in the eastern part of the 

field could be done with confidence. 

More than 200 of the Brunhes vents and flows not 

assigned to vents were placed in the older part of the 

Brunhes by Wolfe and others (1987). These rocks are 

dominantly basalts, but they include a few benmoreites, 

basaltic andesites, and andesites. All the vents are located 

in areas covered by the central and eastern sheets and the 

SP Mountain quadrangle, although a few flows from 

these vents traveled into areas mapped on the east side of 

the southwest sheet and the southeast corner of the 

northwest sheet. Most of the vents in the central sheet are 

west of San Francisco Mountain, and they have 10 K-Ar 

ages ranging from 0.72±0.12 to 0.33±0.08 Ma. In the SP 

Mountain quadrangle, the older Brunhes basalts erupted 

during the Tappan basaltic stage (fig. 5); their K-Ar ages 

range from 0.77±0.04 to 0.22±0.05 Ma. In the eastern 

part of the field, older Brunhes vents range in K-Ar age 

from 0.59±0.09 to 0.17±0.06 Ma (Moore and Wolfe, 

1987); more than 100 vents in this area were not sampled 

paleomagnetically because they have been interpreted to 

be older Brunhes in age on the basis of geomorphic 

relations and their K-Ar ages (Moore and others, 1976). 

According to the Little Colorado River valley stratigraphy, the Merriam basaltic stagefollowed the Tappan 

basaltic stage. Rocks of the Merriam age group are 

equivalent in age to those of the younger Brunhes 

(generally less than about 150,000 years old). In the SP 

Mountain quadrangle, the basaltic andesite of SP Mountain (vent 5703, 71±4 ka age; Baksi, 1974) and basalts of 

vents 5734A-E are placed in the Merriam age group. The 

only verified younger Brunhes vent in the central part of 

the field is Saddle Mountain (vent 4626), from which 

pyroclastic material erupted and buried Walker Lake 

sedimentary deposits dated by 14C as 17 ka (S.W. Robinson, written commun., 1983). In the area of the eastern 

sheet, nine vents are placed in the younger Brunhes; 

these rocks have K-Ar ages of 150±30 ka (flow from vent 

3034 or 3036), 55± 14 ka (O'Neil Crater, vent 2929), and 

51±46 ka (Strawberry Crater, vent 4920). We made 

polarity determinations of all these vents and of the flow. 

The youngest eruptions of the volcanic field occurred exclusively in the area of the eastern sheet during 

the Sunset basaltic stage; their source was a line of vents 

that include Sunset Crater (vent 3824). On the basis of 

dendrochronology (Smiley, 1958) and recent secular 

variation of the geomagnetic pole position, Champion 

(1980; written commun., 1985) inferred that this volcanic 

activity lasted from A.D. 1065 to about 1220. • 

Polarity Chronostratigraphy 11 
Table 2. Mean remanent magnetic directions, virtual geomagnetic pole (VGP) positions, and other 

statistics of chronozones in the San Francisco volcanic field sites, Arizona 

[N, normal; R, reversed; Nav• number of site means averaged; N1, total number of sites in catego:ry; Dec, 

declination; Inc, inclination (minus sign, reversed inclination); cx95, Fisher's 95-percent confidence region of the 

mean (in degrees); "' Fisher's concentration parameter; Lat, latitude north (minus sign, latitude south); Long, 

longitude west; Ap and 11m, semiminor (p) and semimajor (m) axial lengths of the 95-percent confidence oval of 

the mean VGP] 

Mean remanent magnetic direction Mean VGP position (

0

) 

Chronozone Polarity 

NavfNt Dec r) 

Brunhes N 164/184 356.7 

Matuyama N 28/36 349.3 

Matuyama R 232/256 181.3 

Pre-Matuyama N 74/84 357.8 

Pre-Matuyama R 93/97 184.7 

VIRTUAL GEOMAGNETIC POLE POSITIONS 

From mean magnetic vectors of the samples (table 

4 ), we calculated the average remanence directions and 

virtual geomagnetic pole (VGP) locations for each polarity chronozone (table 2). The high dispersions of 

vector directions in each polarity chronozone (table 2; 

see also fig. 4) are due in part to secular variation, but 

they are also due to a variety of site-specific factors, 

including lack of sun-compass orientations for some 

sites, block sampling instead of on-site drilling, local 

rotations of sample outcrops, and lightning-induced remagnetization. Samples of silicic and intermediate rocks 

are particularly susceptible to these effects (see table 4). 

Because of the random nature of the effect of these 

factors on th~. resulting remanent magnetic vectors and 

the large number of sites when grouped altogether 

according to polarity chronozone, the mean of the vectors 

should closely approximate the true mean magnetic 

vector for the time period involved. 

Our derived mean VGP locations correspond 

closely with the present axial geocentric pole position. To 

evaluate the concordance of these pole positions quantitatively, we applied the method developed by Beck (1980, 

p. 7116). If the reference pole is represented by the 

present rotational pole position with a 95-percent confidence interval of 4° (Irving, 1977), our calculated rotation and flattening values indicate that all of the 

determined paleopole positions may be concordant with 

the present axial pole position, given the calculated 

standard deviations of the positions (table 3). 

MIGRATION OF VOLCANISM 

Tanaka and others (1986) reported on the migration of volcanism in the SF field on the basis of the nearly 

complited efforts of many workers in geologic mapping, 

Inc r) 

52.9 

54.5 

-52.1 

51.3 

-53.2 

cx95 r) " Lat Long flp Am 

3.1 13.2 86.6 122.0 3.0 4.4 

7.9 12.8 81.3 158.8 7.9 11.2 

2.6 13.6 -87.1 226.2 2.4 3.6 

4.2 16.2 86.2 97.3 3.9 5.7 

3.5 18.2 -85.9 181.0 3.4 4.9 

Table 3. Rotation and flattening statistics of virtual 

geomagnetic pole (VGP) positions of the San Francisco volcanic field, Arizona 

[After Beck (1980). N, normal; R, reversed. Minus signs, 

counterclockwise for rotation, southward for flattening. Statistics based on expected remanence direction (for normal polarity) of 360" declination, 54.8° inclination, and 95-percent 

confidence about the mean VGP of 4°] 

Chronozone Polarity VGP offset 

Rotation r) Flattening r) 

Brunhes N -3.3±7.1 1.9±3.7 

Matuyama N -10.7±14.5 0.3±8.1 

Matuyama R 1.3±6.5 -2.7±3.3 

Pre-Matuyama N -2.2±8.3 3.5±4.7 

Pre-Matuyama R 4.7±7.6 -1.6±4.0 

paleomagnetic analysis, and K-Ar dating. This 1986 

report showed that both basaltic and silicic volcanism 

migrated northeastward during the Pliocene (Gilbert 

Reversed- and Gauss Normal-Polarity Chronozones) at 

a little more than 1 cm/yr and that the volcanism was 

centered along the Mesa Butte fault from Bill Williams 

Mountain to Sitgreaves Mountain. During the Quaternary (Matuyama Reversed- and Brunhes Normal-Polarity Chronozones ), basaltic volcanism (accompanied by 

the more structurally controlled silicic and intermediate 

volcanism) migrated eastward at about 3 em/yr. Concomitant with the acceleration in migration rate were increased rates of magma production and eruption 

frequency. Tanaka and others (1986) used this eruptive 

history to construct a magma-generation model for the 

field that involves basal shearing of the lithosphere, which 

provided the heat to produce the magmas that formed 

the volcanic field. 

12 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
At present, detailed geologic mapping and documentation of the K-Ar ages are virtually complete (Wolfe 

and others, 1987). In this report, we have fully documented the paleomagnetism and magnetostratigraphy of the 

volcanic field. The preliminary magnetostratigraphy 

summarized in Tanaka and others {1986) has changed 

very little. (The geologic maps, K-Ar data, and paleomagnetic work were unpublished at the time but available to them.) Our modest refinements in the 

paleomagnetic work include some further demagnetizations of some sites, resulting in improved magnetic 

vectors. We also slightly changed the classification of the 

vents, adding some benmoreite, basaltic andesite,. and 

andesite vents to our "basaltic rocks" category to harmonize with the vent-numbering system on the geologic 

maps. Therefore, we now have a few more vents and a 

few less silicic and intermediate sample sites than were 

cited in Tanaka and others {1986). We carried out no 

further field work. 

Because these changes are few and insignificant, 

they do not necessitate reevaluation of the overall migrational history of the field. In other words, we judge that 

the estimates of migration of volcanism and of the 

evolution in magma production and eruption frequency 

that were reported in Tanaka and others {1986) are still 

reasonably accurate, given the uncertainties involved 

(such as degree of structural control, accuracy of volume 

estimates, and stratigraphic inferences). 

Moreover, Tanaka and others {1986) suggested 

that the recent eastward migration of volcanism was 

related to westward motion of the North American plate 

over the fiXed, deep mantle. In support of this hypothesis, 

they noted that K-Ar ages (Best and Brimhall, 1974) 

indicate eastward migration of volcanism in late Cenozoic volcanic rocks of the Uinkarets-Shivwits Plateau north 

of the Grand Canyon of the Colorado River. In the 

Springerville volcanic field rocks of east-central Arizona, 

Condit and others (1987) found (1) eastward migration 

of about 3.0 cm/yr in 101 alkali-olivine basalt vents and 

(2) eastward migration of about 2.5 cm/yr for all dated 

vents. The rocks in their study are less than 2 m.y. old and 

were dated by K-Ar ages, paleomagnetic data, and stratigraphic relations. 

CONCLUSIONS 

On the basis of paleomagnetic polarity determinations, K-Ar and other absolute ages, and stratigraphic 

relations, we have assigned about 600 separate eruptive 

units to the pre-Matuyama (Gilbert and Gauss), Matuyama, and Brunhes Chronozones. This methodology is 

efficient, and it is much less costly than radiometric 

dating alone. It is also comprehensive, raising the stratigraphy of a large volcanic field to levels of detail and 

precision previously unmatched. The stratigraphy provides a basis for speculating on the causes of magma 

generation in intraplate continental volcanic fields and on 

the absolute motion of the North American plate (Tanaka and others, 1986), and it provides a comprehensive 

framework for future considerations of petrogenetic 

processes and for assessment of volcanic hazards. 

Our dataset also allows for statistical analysis of 

secular variation and other paleomagnetic studies. Analysis of average VGP positions shows no demonstrable 

rotation or translation of the rocks in the volcanic field. 

REFERENCES CITED 

Babbitt, B.E., 1963, A paleom.agnetic study of the San Francisco volcanic field, Arizona: University of Durham, England, 

King's College, M.S.C. thesis, 58 p. 

Baksi, A.K., 1974, K-Ar study of the SP flow: Canadian Journal 

of Earth Science, v. 11, no. 10, p. 1350-1356. 

Beck, M.E., Jr., 1980, Paleomagnetic record of plate-margin 

tectonic processes along the western edge of North America: Journal of Geophysical Research, v. 85, no. B12, p. 

7115-7131. 

Best, M.G., and Brimhall, W.H., 1974, Late Cenozoic alkalic 

basaltic magmas in the western Colorado Plateaus and the 

Basin and Range transition zone, U.S.A., and their bearing 

on mantle dynamics: Geological Society of America Bulletin, v. 85, no. 11, p. 1677-1690. 

Champion, D.E., 1980, Holocene geomagnetic secular variation in the western United States: implications for global 

geomagnetic field: U.S. Geological Survey Open-File Report 80-824, 314 p. 

Coe, R.S., 1967, Paleo-intensities of the Earth's magnetic field 

determined from Tertiary and Quaternary rocks: Journal 

of Geophysical Research, v. 72, no. 12, p. 3247-3262. 

Colton, H.S., 1936, The basaltic cinder cones and lava flows of 

the San Francisco Mountain volcanic field: Flagstaf, Ariz., 

Museum of Northern Arizona, Bulletin (10], 58 p. [revised 

edit., 1967). 

Condit, C.D., Aubele, J.C., and Crumpler, L.S., 1987, Volcanic 

record of the Springerville volcanic field, east-central 

Arizona: Geological Society of America Abstracts with 

Programs, v. 19, no. 7, p. 625. 

Cooley, M.E., 1962, Geomorphology and the age of volcanic 

rocks in northeastern Arizona: Arizona Geological Society 

Digest, v. 5, p. 97-115. 

Cox, A.V., Doell, R.R., and Dalrymple, G.B., 1964, Reversals 

of the Earth's magnetic field: Science, v. 144, no. 3626, p. 

1537-1543. 

Dalrymple, G.B., 1979, Research note: critical tables for conversion of K-Ar ages from old to new constants: Geology, 

v. 7, no. 11, p. 558-560. 

Damon, P.E., 1966, Correlation and chronology of ore deposits 

and volcanic rocks: U.S. Atomic Energy Commission Annual Progress Report C00-689-60, 46 p. 

Damon, P.E., Shafiqullah, Muhammed, and Leventhal, J.S., 

1974, K-Ar chronology for the San Francisco volcanic field 

and rate of erosion of the Little Colorado River, in 

Karlstrom, T.N.V., Swann, G.A., and Eastwood, R.L., eds, 

Geology of northern Arizona, with notes on archaeology 

References Cited 13 
and paleoclimate; Part I, Regional studies: Geological 

Society of America, Rock-y Mountain Section Meeting, 

27th, Flagstaff, Ariz., 1974, p. 221-235. 

Doell, R.R., and Cox, A.V., 1965, Measurement of the remanent magnetization of igneous rocks: U.S. Geological 

Suxvey Bulletin 1203-A, p. 1-32. 

liVing, E., 1977, Drift of the major continental blocks since the 

Devonian: Nature, v. 270, no. 5635, p. 304-309. 

Luedke, R.G., and Smith, R.L., 1978, Map showing distribution, composition, and age of late Cenozoic volcanic 

centers in Arizona and New Mexico: U.S. Geological 

Suxvey Miscellaneous Investigations Series Map I-1091-

A, scale 1:1,000,000. 

Mankinen, E.A., and Dalrymple, G.B., 1979, Revised geomagnetic polarity time scale for the intexval 0-5 m.y. B.P.: 

Journal of Geophysical RC$earch, v. 84, no. B2, p. 615-

626. 

*Moore, R.B., and Wolfe, E.W., 1987, Geologic map of the east 

part of the San Francisco volcanic field, north-central 

Arizona: U.S. Geological Suxvey Miscellaneous Field 

Studies Map MF-1960, scale 1:50,000. 

Moore, R.B., Wolfe, E.W., and Ulrich, G.E., 1976, Volcanic 

rocks of the eastern and northern parts of the San Francisco volcanic field, Arizona: U.S. Geological Suxvey Journal of Research, v. 4, no. 5, p. 549-560. 

*Newhall, C.G., Ulrich, G.E., and Wolfe, E.W., 1987, Geologic 

map of the southwest part of the San Francisco volcanic 

field, north-central Arizona: U.S. Geological Suxvey Miscellaneous Field Studies Map MF-1958, scale 1:50,000. 

Opdyke, N.D., and Runcorn, S.K., 1956, Remanent magnetization of lava flows in northern Arizona: Flagstaff, Ariz., 

Museum of Northern Arizona, Plateau, v. 29, p. 1-5. 

Robinson, H.H., 1913, The San Franciscan volcanic field, 

Arizona: U.S. Geological Suxvey Professional Paper 76, 

213 p. 

Shoemaker, E.M., Squires, R.L., and Abrams, M.J., 1978, 

Bright Angel and Mesa Butte fault systems of northern 

Arizona, in Smith, R.B., and Eaton, G.P., eds., Cenozoic 

tectonics and regional geophysics of the western CordilJera: Geological Society of America Memoir 152, p. 341-

368. 

Smiley, T.L., 1958, The geology and dating of Sunset Crater, 

Flagstaff, Arizona, in Anderson, R.Y., and Harshbarger, 

eds., Guidebook of the Black Mesa Basin: New Mexico 

Geological Society Field Conference, 9th, Gallup, N.M., 

1958, p. 186-190. 

Smith, R.L., and Luedke, R.G., 1984, Potentially active volcanic 

lineaments and loci in western conterminous United 

States, in Geophysics Study Committee, ed., Explosive 

volcanism: inception, evolution, and hazards: Washington, 

D.C., National Academy Press, p. 47-66. 

Strangway, D.W., McMahon, B.E., and Larson, E.E., 1968, 

Magnetic paleointensity studies on a recent basalt from 

Flagstaff, Arizona: Journal of Geophysical Research, v. 73, 

no.22,p. 7031-7037. 

Tanaka, K.L., Shoemaker, E.M., Ulrich, G.E., and Wolfe, E.W., 

1986, Migration of volcanism in the San Francisco volcanic 

field, Arizona: Geological Society of America Bulletin, v. 

97, no. 2, p. 129-141. 

*Ulrich, G.E., and Bailey, N.G., 1987, Geologic map of the SP 

Mo~mtain part of the San Francisco volcanic field, northcentral Arizona: U.S. Geological Suxvey Miscellaneous 

Field Studies Map MF-1956, scale 1:50,000. 

Ulrich, G.E., and Nealey, L.D., 1976, Structural and eruptive 

patterns in the San Francisco volcanic field, northern 

Arizona: Geological Society of America Abstracts with 

Programs, v. 8, no. 5, p. 641-642. 

*Wolfe, E.W., Ulrich, G.E., Holm, R.F., Moore, R.B., and 

Newhall, C.G., 1987a, Geologic map of the central part of 

the San Francisco volcanic field, north-central Arizona: 

U.S. Geological Suxvey Miscellaneous Field Studies Map 

MF-1959, scale 1:50,000. 

Wolfe, E.W., Ulrich, G.E., and Moore, R.B., 1983, San Francisco volcanic field, Arizona: Volcano News, no. 13, p.1-3. 

*Wolfe, E.W., Ulrich, G.E., and Newhall, C.G., 1987b, Geologic map of the northwest part of the San Francisco 

volcanic field, north-central Arizona: U.S. Geological Survey MisceJlaneous Field Studies Map MF-1957, scale 

1:50,000. 

*These five maps are collectively referenced in this report as 

"Wolfe and others, 1987." 

14 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 
TABLE 4 

Table 4 provides paleomagnetic data acquired for sample sites in the San 

Francisco volcanic field, Arizona (for specific map locations, see Wolfe and others, 

1987). The sites are grouped according to their inferred polarity chronozone 

(pre-Matuyama, Matuyama, or Brunhes). Within these categories, silicic and intermediate rocks are grouped together according to their association with silicic centers 

and whether or not K-Ar ages have been determined (from Wolfe and others, 1987, 

unless otherwise noted). Basaltic rocks are organized according to degree of certainty 

in their age determinations: those having K-Ar ages; those having conclusive field 

relations; those dated primarily by paleomagnetic data and other, less conclusive 

information; and those whose determinations are largely uncertain. Dashes indicate 

that data are unreliable or not available. Footnotes are at end of table. 

Sample sites are identified by a four-digit numbering system developed by Wolfe 

and others (1987). The first digit of the sample number represents the township 

(second digit of the township number), the second digit represents the range, and the 

last two digits are the section number in which the site is located. (Because the second 

digit 1 could represent R. 1 W., R. 1 E., and R. 11 E., Z represents R. 1 W., and A 

represents R. 11 E. See figure 2). Where more than one site occurs within a section, 

a letter suffix has been added to subsequent samples for unique identification. Most 

of the basaltic vents, which represent discrete eruptive units, are identified by this 

same labeling method (second column); the vent identification numbers correspond 

to those used by Wolfe and others (1987). Samples having silicic to intermediate 

composition are identified according to composition and site location. The type of 

volcanic feature sampled (for example, vent, flow, or dike) is indicated in the third 

column. 

As applicable, the following information is also provided for each sample site: (1) 

Map sheet showing sample site (Wolfe and others, 1987; see fig. 2): C, central; E, east; 

NW, northwest; SW, southwest; SP, SP Mountain. (2) Latitude and longitude. (3) 

Number of samples averaged in paleomagnetic vector (Nav) and total number of 

samples taken (Nt); only the total number is shown if no average statistics are 

presented. ( 4) Polarity of magnetic vector. ( 5) Declination (Dec) and inclination (Inc) 

of average magnetic vector (minus sign = reversed inclination). (6) Fisher's 95-

percent confidence region of the mean magnetic vector (a95 ). (7) Fisher's concentration parameter (K). (8) Alternating-field demagnetization (AFD) intensity for the 

statistics (measured in oersteds; NRM = natural remanent magnetization). (9) Field 

relations to rocks at other sites. (10) K-Ar age (or other absolute age, where available) 

in million years. Where polarity determinations have high dispersion ( a95 > 40°) or 

questionable mean direction, the polarity is queried and the paleomagnetic data are 

not included. Field relations are based on superposition relations and eruptive 

associations (for example, the relation of flows to the vents from which they issued) as 

portrayed on the geologic maps. (Where applicable in these relations, vent numbers 

of basaltic rocks are used; otherwise, site numbers are used.) Paleomagnetic studies 

were not made for rocks noted as "unsampled." Field relations that are queried relate 

to the uncertainty in the identification of the eruptive source of the sampled unit, not 

to the uncertainty of the field relation. 

James N. Kellogg of the U.S. Geological Survey graciously provided unpublished 

paleomagnetic results. Field, laboratory, and other assistance was provided by 

personnel of the U.S. Geological Survey Paleomagnetics Laboratory in Flagstaff, 

Ariz., including Donald P. Elston, James H. Hiekey, Edmund G. Kelley, William 

Power, and Cecilia S. Tanaka. 

Table 4 15 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, Arizona 

[Abbreviations are explained on preceding page) 

Location Mean remanent magnetism 

sne No. 

2233 

1209B 

1203 

1218 

1218A 

1207 

1217 

1217A 

2222A 

2221 

1122 

1205 

1202A 

1204 

1209A 

1221A 

3428 

3433A 

Rock type 

or vent No. 

Dacite 

Dacite 

Dacite 

Dacite 

Dacite 

Dacite 

Dacite 

Dacite 

Andesite 

Andesite 

Benmoreite 

Andesite 

Dacite 

Dacite 

Dacite 

Dacite 

Rhyolite 

Rhyolite 

3428A Rhyolite 

1232A 

3422 

2410 

3434 

1222 

2135 

1710 

5634 

1233 

1233A 

2520 

Dacite 

Rhyolite 

Rhyolite 

Rhyolite 

1222 

2135 

Basalt 

4609 

1233 

1233 

2519B 

Feature 

Flow 

Dome 

Flow 

Dome 

Dome 

Dome 

Flows 

Dome 

Dome 

Dome 

Flow 

Flow 

Dome 

Dome 

Dome 

Dome 

Dome 

Flow 

Flow 

Dome 

Dome 

Dome 

Dome 

Vent 

Vent 

Flow 

Flow 

Dike 

Vent 

Vent 

Map 

sheet 

sw 

SW 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

c 

c 

c 

sw 

c 

c 

c 

sw 

SW 

c 

SP 

sw 

SW 

c 

35.24 

35.21 

35.23 

35.20 

35.20 

35.22 

35.21 

35.22 

35.27 

35.27 

35.18 

35.24 

35.23 

35.23 

35.22 

35.20 

35.35 

35.34 

Nav!Nt 

(orNt) Polarity 

PRE-MATUYAMA ROCKS 

SILICIC AND INrERMEDIATE ROCKS 

Bill Willinms Mountain rocks, dated 

11218 

11219 

112.19 

112.23 

112.22 

112.23 

11221 

11221 

11217 

11218 

11227 

112.21 

6/6 

6/6 

6/6 

5/6 

5/6 

4/8 

6/6 

4/6 

5!6 

6/6 

6/6 

6/6 

N 

N 

N 

N 

R 

N 

N 

N 

N 

N 

R 

N 

5 

14 

16 

13 

163 

14 

24 

354 

316 

335 

188 

7 

0 

71 

57 

36 

-41 

14 

6 

32 

20 

11 

-40 

30 

Bill Williams Mountain rocks, undated 

11215 

11218 

112.20 

11219 

111.98 

111.98 

515 

6 

6/6 

6 

R 

R? 

R 

N? 

190 -38 

175 ...:39 

Sitgreaves Mountain rocks, dated 

6!6 

6!6 

N 

N 

3 

'331 

47 

41 

Sitgreaves Mountain rocks, undated 

35.35 111.98 5!6 N 57 

35.15 

35.36 

35.30 

35.33 

35.19 

35.24 

35.22 

35.51 

35.15 

35.16 

35.27 

11221 

111.96 

111.% 

111.96 

112.17 

112.25 

111.64 

111.73 

11218 

112.18 

111.88 

Miscellaneous rocks, dated 

6/6 

6/6 

7/9 

4/6 

R 

N 

R 

R 

196 

346 

217 

176 

BASALTIC ROCKS 

Dated 

6!6 

4/6 

4/6 

6/6 

6/6 

6 

6/6 

R 

R 

R 

R 

R 

R? 

N 

168 

176 

188 

170 

141 

345 

-56 

30 

-58 

-43 

-48 

-50 

-45 

-56 

-61 

54 

16 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

7 

4 

4 

6 

3 

9 

6 

18 

8 

8 

16 

10 

104 

275 

306 

145 

545 

106 

115 

26 

94 

71 

18 

50 

7 117 

10 47 

AFD 

(Oe) 

500 

250 

250 

250 

250 

750 

500 

500 

250 

500 

250 

250 

50 

500 

Field relations 

Younger than basalt 1710. 

Younger than 

1209. 

Older than 1202----

Older than 2222----

Same as site 

2222A. 

Younger than basalt 1710, 2232 

5 

10 

181 NRM 

48 250 Older than 3433, 

rhyolite 3433B. 

8 71 

6 

13 

8 

13 

7 

12 

9 

7 

7 

7 

138 

28 

62 

51 

98 

57 

100 

87 

93 

81 

250 Younger than rhyolite 3433A. 

250 

250 

250 

250 

250 

500 

500 

330 

250 

250 

Older than rhyolite 

2405A, 3421. 

Older than 1211, 

1227. 

Older than 2133----

Older than 1219; 

younger than 

1232 

Same as site 1233--

Older than 2519A -

K-Arage 

(Ma) 

5.03±0.50 

4.22±0.26 

4.17±1.06 

3.88±0.44 

3.72±0.21 

3.62±0.33 

356±0.38 

3.49±0.06 

3.48±0.05 

294±057 

285±0.91 

2.85±0.06 

284±0.02 

5.15±0.17 

288±0.09 

279±0.07 

274±0.16 

6.38±0.32 

6.13±0.15 

5.82±0.34 

5.62±0.19 

4.17±0.39 

4.12±0.20 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

sne No. 

2233A 

6806 

1211 

0102 

0305 

0506 

0616 

0626 

1101 

1102 

1104 

1105 

1109 

1110 

1123 

1133 

1134 

1134A 

1202 

1209 

1216 

1221 

1221B 

1223 

1224 

1224B 

1226 

1227 

1232 

1234 

1234A 

1236 

1319 

1328 

1330 

1330A 

1331 

1331A 

1331B 

1332 

1505 

Rock type 

or vent No. 

Basalt 

6806 

1211 

0102 

0305 

0506 

0616 

0626 

1101 

1102 

1104 

1105 

1109 

1110 

1123 

0104 

1134A 

0103 

1202 

1209 

Basalt 

1221 

1221A 

1223 

1224 

1224B 

1226 

1227 

1232 

1234 

1234A 

1236 

1319 

1334 

1330 

1330A 

1331 

1331A 

Basalt 

1329 

1505 

1505A 1505 

Feature 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Dike 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Map 

sheet 

sw 

SP 

sw 

sw 

sw 

c 

c 

c 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

SW 

sw 

sw 

sw 

sw 

sw 

SW 

sw 

sw 

SW 

sw 

sw 

c 

c 

Location Mean remanent magnetiSm 

35.24 

35.66 

35.22 

35.14 

35.15 

35.14 

35.12 

35.08 

35.23 

35.22 

35.22 

35.23 

35.22 

35.22 

35.17 

35.15 

35.15 

35.15 

35.23 

35.22 

35.20 

35.18 

35.16 

35.18 

35.19 

35.19 

35.17 

35.17 

35.16 

35.16 

35.16 

35.16 

35.18 

35.17 

35.17 

35.17 

35.16 

35.16 

35.16 

35.16 

35.23 

Dec 

Polarity ( o ) 

PRE-MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Dated-Continued 

11218 

11158 

11216 

11226 

112.10 

111.90 

111.n 

111.74 

11224 

11225 

11229 

11231 

11229 

11228 

11226 

11228 

11227 

11228 

11215 

112.18 

11218 

112.19 

112.16 

11215 

11213 

11214 

11215 

11216 

11221 

112.17 

112.16 

11213 

112.12 

11208 

11211 

112.12 

112.11 

11212 

11211 

11210 

111.88 

6/6 

6/6 

6/6 

5/6 

6/6 

8/9 

5!6 

6/6 

6/6 

6/6 

4/6 

6/6 

6/6 

6/6 

6 

5!6 

5/6 

6/6 

6/6 

5/6 

4/6 

6/6 

6/6 

6 

6/6 

6 

4/6 

5/6 

5/6 

6/6 

6/6 

6/6 

6!6 

4/6 

6/6 

6/6 

5!6 

6/6 

616 

5/6 

6n 

R 

N 

N 

Undated 

R 

N 

R 

R 

R 

R 

R 

N 

N 

R 

N 

R? 

N 

N 

N 

N 

R 

N 

R 

N 

N? 

N 

N? 

N 

R 

N 

R 

R 

R 

R 

R 

R 

R 

N 

R 

R 

R 

R 

207 

355 

9 

-57 

47 

73 

199 -44 

353 61 

165 -57 

214 -45 

115 -47 

178 -41 

181 -44 

3~5 49 

6 51 

172 -46 

355 35 

350 50 

6 40 

5 46 

338 26 

190 -46 

335 58 

168 -59 

347 48 

346 48 

5 42 

227 -59 

59 

188 -48 

121 -35 

158 -36 

219 -49 

182 -52 

184 -56 

174 -9 

4 50 

160 -34 

184 -57 

179 -56 

180 -42 

8 

21 

2 

75 

11 

1229 

3 760 

2 812 

7 68 

6 161 

4 305 

4 282 

3 556 

2 2181 

5 214 

4 235 

5 218 

5 203 

1 4324 

5 203 

3 475 

33 6 

12 60 

3 655 

5 157 

3 485 

18 28 

23 12 

5 240 

2 1676 

6 110 

2 1018 

6 115 

7 188 

2 1227 

2 1382 

2 1367 

4 360 

3 425 

12 39 

12 31 

35.2l 111.89 6/6 R 172 -42 29 6 

AFO 

(Oe) 

250 

750 

250 

250 

250 

250 

500 

250 

250 

250 

500 

250 

250 

250 

250 

250 

250 

250 

500 

500 

500 

250 

250 

250 

500 

250 

250 

250 

250 

250 

250 

250 

250 

250 

250 

250 

250 

250 

Field relations 

Older than dacite 

2233, andesite 

(uosampled. 

3.20±0.60 Ma). 

andesite 1205. 

Younger than 

1222, 1224. 

Younger than 

1331. 

Older than Oak 

Creek fault. 

Older than 2124 ----

Older than 2124----

Younger than dacite 1203. 

Older than dacite 

1209B. 

Older than 1211----

Older than 1224A -

Younger tban 

1222. 

Older than 1233---

Younger than 

1234A. 

Older than 1234 ----

Older than 0305, 

1331; younger 

than 1331A. 

Older than 1505A, 

2531. 

500 Same as site 1505 --

K-Arage 

(Ma) 

4.03±051 

3.13±0.39 

284±0.25 

Table 4 17 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

1508 

2Z10 

2Z22 

2Z23 

2Z23A 

2Z23B 

2Z24 

24A 

2'Z25 

2'Z25A 

2Z'lf:J 

2101 

2102 

2104 

2105 

2105A 

2105B 

2110 

2110A 

2111 

2113 

2114 

2114A 

2116 

2116A 

2117 

2122 

2122A 

2123 

2124 

2124A 

2125 

2125A 

2126 

2127 

2127A 

Rock type 

or vent No. 

1508 

2Z03 

2Z27 

2Z23 

2Z23A 

2Z23A 

2Z24 

2119 

2'Z25 

2'Z25A 

2Z26 

2101 

2102 

2104 

2105 

2105A 

2105? 

2110 

2110A 

2112 

2113 

211~ 

2114A 

2116 

2109 

2108 

2122 

2127 

2123 

2124 

2124C 

2125 

2125B 

2126 

2127B 

2128 

Feature 

Vent 

Flow 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Dike 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Flow 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Dike 

Vent 

Vent 

Vent 

Vent 

Map 

sheet 

c 

SW 

sw 

sw 

sw 

sw 

sw 

SW 

sw 

sw 

sw 

SW 

SW 

sw 

SW 

sw 

sw 

sw 

SW 

sw 

sw 

sw 

sw 

SW 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

Location Mean remanent magnetism 

35.22 

35.30 

35.27 

35.27 

35.27 

35.27 

35.27 

35.27 

35.26 

35.26 

35.25 

3531 

3531 

35.32 

35.32 

35.32 

35.32 

35.30 

35.30 

35.30 

35.29 

35.28 

35.28 

35.29 

35.29 

35.29 

35.27 

35.26 

35.25 

35.27 

35.27 

35.26 

35.26 

35.25 

35.26 

35.26 

Nav!Nt 

(or Nt) Polarity 

AFD 

(Oe) 

PRE-MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

111.90 

11238 

112.39 

11236 

112..15 

112.36 

11235 

112.34 

112.35 

11235 

11236 

112.25 

11225 

11229 

112.31 

112.30 

11231 

11227 

112.27 

11225 

11224 

112.25 

11225 

11228 

112.29 

11230 

11227 

112.27 

11225 

11223 

112.24 

11223 

112.23 

112.25 

112.27 

11229 

5!9 

6/6 

6/6 

6/6 

5!6 

6/6 

4/6 

4/6 

6/6 

5!5 

6/6 

• 5!6 

5/6 

6!6 

6/6 

6/6 

4/6 

6/6 

6!6 

4/6 

5!6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

6/6 

5/6 

516 

6/6 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

N 

R 

R 

N 

N 

N 

R 

R 

R 

R 

N 

N 

R 

R 

R 

R 

R 

N 

R 

R 

R 

R 

R 

R 

N 

R 

169 -48 

219 -44 

180 -67 

199 -37 

162 -78 

147 -46 

207 -53 

183 -45 

204 -35 

181 -66 

341 38 

177 -72 

212 -69 

12 68 

3 51 

335 68 

183 -59 

157 -58 

156 -63 

205 -70 

32 54 

46 39 

190 -64 

216 -36 

225 -57 

1n -57 

176 -50 

24 55 

147 -49 

169 -65 

213 -72 

175 -59 

185 -59 

235 -32 

357 46 

175 -52 

5 210 250 

9 54 500 

6 108 500 

7828 250 

15 27 750 

25 8 750 

19 25 750 

10 92 250 

3 515 250 

5 210 500 

3 541 250 

3 490 250 

3 684 250 

3 406 250 

6 127 250 

3 633 250 

32 7 250 

15 20 500 

3 499 250 

5 320 250 

2 1083 250 

21 11 250 

4 224 500 

2 1849 250 

4 339 250 

5 212 500 

4 236 250 

8 71 250 

9 62 1000 

3 715 250 

3 489 250 

4 311 250 

3 438 250 

4 325 250 

22 13 1000 

2 724 250 

18 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

FJeld relations 

Older than 1505A, 

2531A. 

Older than 2122, 

3132A; younger 

than 3Z33. 

Older than 2Z03-

Younger than 

2'Z25A. 

Younger than 

2119,2122. 

Same as site 

2Z23A. 

Older than 2Z23AOlder than 2Z26 ---

Older than 2Z03, 

2Z2.:t 

Younger than 

2'Z25. 

Younger than 

2105, 2110, 2122. 

Older than 2104----

Older than 2104? --

Older than 2104, 

2112, 2122. 

Older than 2113, 

2220; younger 

than 2110, 

2125B. 

Younger than 

2112, 2125B. 

Younger than 

2122. 

Older than 2Z23A, 

2104, 2108, 2127, 

2133, 3132A; 

younger than 

2Z03, 2110. 

Younger than 

2122 

Younger than 

1101. 

Older than 2125C 

(unsampled). 

Older than 2133? --

K-Arage 

(Ma) 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

sne No. 

2128 

2128A 

2133 

2133A 

2136 

2136A 

2214 

2215 

2217 

2217A 

2218 

2219 

2219A 

2219B 

2219C 

2222 

2230 

2232 

2319 

2319A 

2319B 

2319C 

23190 

2320 

2421A 

2435 

2531B 

3Z13 

3Z23 

3Z23A 

3Z28 

Rock type 

or vent No. 

2133 

2127A 

2133B 

2133A 

2136 

2136A 

2214 

2215 

2217 

2220 

2218 

2219 

2219 

Basaltic 

andesite 

Andesite 

2222 

22.10 

2232 

2319 

2319 

2319 

2319A 

2319B 

2320 

2421A 

2436 

1506 

3Z13 

3Z23 

3Z23A 

3Z.13A 

Feature 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Flow 

Flow 

Vent 

Flow 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Map 

sheet 

SW 

SW 

SW 

sw 

sw 

SW 

sw 

SW 

SW 

SW 

SW 

SW 

SW 

SW 

SW 

SW 

sw 

SW 

SW 

SW 

SW 

SW 

SW 

SW 

c 

c 

c 

sw 

sw 

SW 

SW 

Location Mean remanent magnetism 

35.25 

35.26 

35.24 

35.25 

35.24 

35.24 

35.29 

35.29 

35.29 

35.29 

35.29 

35.27 

35.27 

35.27 

35.27 

35.27 

35.26 

35.25 

35.27 

35.27 

35.27 

35.27 

35.28 

35.27 

35.27 

35.24 

35.23 

35.37 

35.36 

35.36 

35.34 

NavfNt 

(or Nt) Polarity 

PRE-MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

11229 

112.28 

112.29 

112.29 

11224 

112.24 

112.15 

112.16 

11220 

112.21 

11222 

11223 

11223 

11222 

112.22 

11217 

11222 

11221 

11212 

11211 

11211 

11212 

11212 

11209 

111.97 

111.93 

111.91 

11236 

112.36 

112.41 

515 

5/5 

6/6 

4/6 

616 

5/6 

516 

6/8 

6/6 

6/6 

5/6 

6/6 

6/6 

516 

5/6 

516 

6/6 

616 

516 

516 

5/6 

4/6 

516 

6/8 

6/6 

5n 

618 

6/6 

5/6 

6/6 

515 

R 

R 

N 

N 

R 

R 

R 

R 

R 

N 

R 

R 

R 

N 

N 

N 

R 

R 

N 

N 

N 

N 

R 

N 

R 

R 

R 

R 

R 

R 

R 

229 

171 

358 

359 

204 

195 

206 

190 

219 

352 

179 

184 

148 

10 

0 

348 

165 

181 

2 

346 

354 

346 

189 

338 

165 

174 

202 

198 

172 

180 

219 

-44 

-27 

53 

51 

-31 

-48 

-45 

-54 

-63 

52 

-28 

-54 

-52 

55 

58 

52 

-57 

-63 

56 

52 

61 

50 

-58 

44 

-42 

-55 

-40 

-56 

-61 

-74 

-41 

13 

7 

11 

6 

6 

16 

9 

4 

5 

7 

4 

2 

3 

6 

6 

7 

6 

3 

4 

28 

4 

12 

11 

21 

4 

3 

29 

33 

4 

5 

4 

37 

139 

35 

261 

149 

25 

73 

350 

180 

103 

383 

830 

544 

150 

147 

138 

122 

671 

374 

8 

343 

56 

48 

10 

260 

523 

6 

5 

427 

210 

318 

AFD 

(Oe) 

1000 

250 

500 

250 

250 

500 

250 

250 

750 

250 

1000 

250 

250 

250 

NRM 

NRM 

250 

250 

250 

750 

250 

250 

250 

250 

250 

NRM 

250 

500 

250 

500 

250 

Field relations 

Younger than 

2122, 2127B?, 

2133B, 2135, 

2136A. 

Older than 2133----

Older than 2133---

Older than 2212, 

2319A; younger 

than 2220. 

Older than 2220?, 

2222'! 

Older than 2203, 

2215, 2222, 

3229; younger 

than 2112, 

2217'!, 2218, 

3136, andesite 

2222A. 

Older than 2220----

Younger than andesite 2219C. 

Same as site 2219--

Older than 2220----

Older than 2219----

0lder than 2319A; 

younger than 

2217?, 2220, andesite 2222A. 

Older than andesite 

1205. 

Older than 2320----

Same as site 2319 --

Same site 2319------

Younger than 

2215,2222 

Older than 2303, 

2308A, 2316A; 

younger than 

2119. 

Older than 2416----

Older than 1505A, 

2531A. 

Younger than 

3Z21A, 3Z33A, 

3118. 

Younger than 

3Z23A. 

Older than 3Z13, 

3Z23. 

Older than 3Z13; 

younger th:m 

3Z33. 

K-Arage 

(Ma) 

Table 4 19 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

3Z33 

3Z33A 

3118 

3121 

3121A 

3126 

3132 

3133 

3135 

3136 

3304 

3304A 

3304B 

3307 

4202 

4226A 

4236 

4236A 

4332 

4332A 

5101 

5206 

5214 

5220 

6135 

6135A 

6135B 

6136 

6806A 

7410 

1303 

1309 

1311 

1315 

1316 

1316A 

2226 

Rock type 

or vent No. 

3Z33 

3'Z29 

3118 

3121 

3121A 

3126 

3132 

3133 

3135 

3136 

3304 

3304A 

3304B 

3307 

4202 

4226A 

4236 

4236A 

4332 

4332A 

5101 

5206 

5214 

5217 

6135 

6135A 

6126 

6136 

Basalt 

7410 

1303 

1316 

1311 

1315 

1316A 

1316A 

2226 

Feature 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

·vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Tuff 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

LocatiOn Mean remanent magnetism 

AFD 

(Oe) Field relatiOns 

PRE-MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

sw 35.33 112.40 

SW 

SW 

sw 

sw 

sw 

SW 

sw 

SW 

SW 

SW 

sw 

sw 

SW 

SW 

sw 

SW 

SW 

sw 

SW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

SP 

NW 

35.34 

35.37 

35.36 

35.36 

35.34 

35.33 

35.33 

35.33 

35.33 

35.40 

35.40 

35.41 

35.39 

35.50 

35.44 

35.41 

35.42 

35.42 

35.41 

35.57 

35.57 

35.54 

35.54 

35.59 

35.60 

35.60 

35.59 

35.66 

35.74 

11241 

11232 

112.29 

11230 

11225 

112.31 

112.13 

112.26 

112.25 

11208 

112.09 

11208 

11211 

112.14 

11214 

11212 

112.13 

112.10 

11209 

11224 

112.22 

11214 

11220 

11225 

112.25 

11226 

112.25 

111.59 

111.95 

sw 35.23 112.05 

SW 35.21 112.08 

SW 35.21 11205 

sw 35.20 112.06 

sw 35.20 112.08 

sw 35.20 

SW 35.25 

112.08 

11215 

6/6 

6/6 

6/6 

6/6 

6/6 

5/6 

5!6 

6/6 

5!6 

6/6 

7/8 

6/6 

6/6 

5!6 

6/6 

5/6 

4/6 

6/8 

6/6 

6 

6 

6/6 

6 

6/6 

6/6 

6 

6 

6/6 

6 

R 

R 

R 

N 

R 

R 

N 

N 

R 

R 

N 

N 

N 

N 

R 

N 

N 

N 

N 

N 

N? 

N? 

N 

R? 

N 

N 

N? 

N? 

N 

N? 

181 -62 

222 -38 

160 -39 

328 23 

200 -64 

254 -62 

33 

46 

165 

163 

6 

9 

338 

16 

205 

298 

5 

17 

347 

13 

338 

348 

353 

5 

48 

47 

-69 

-53 

66 

63 

59 

60 

-36 

53 

53 

62 

61 

68 

63 

58 

73 

66 

Pre-Matuyama or Matuyama 

616 

6/6 

6/6 

6/6 

6 

N 

N 

N 

R 

N? 

345 58 

9 64 

27 33 

156 -54 

3 385 

5 188 

2 751 

34 5 

4 354 

6 169 

2 

3 

3 

6 

4 

25 

24 

6 

7 

7 

15 

5 

7 

13 

15 

19 

5 

12 

1056 

424 

770 

114 

182 

8 

9 

157 

94 

118 

21 

388 

84 

23 

22 

14 

158 

31 

500 Older than 2Z03, 

250 

250 

500 

250 

500 

250 

250 

250 

500 

250 

250 

250 

250 

750 

250 

500 

250 

250 

500 

250 

250 

500 

250 

3Z33A, 3132A. 

Older than 3Z13 ---

Older than 3133, 

3136. 

Younger than 

3126. 

Younger than 

3136. 

Older than 2220, 

3135; younger 

than 3113, 3126. 

Older than 4332A -

Older than 3202, 

3306. 

Older thnn andesite 

4213, 4332A?. 

Older than andesite 

4213, 4236A. 

Older than 3306A, 

4226; younger 

than4236A. 

Older than 4236; 

younger than 

4226A. 

Older than 3304A, 

3310, andesite 

4213?, 4327?; 

younger than 

4202? 

Younger than 

4202? 

Older than 6713----

2088 250 Older than Mesa 

Butte fault. 

3 544 250 Older than 1316A4 296 250 Older than 2335A -

4 236 250 Older than 1316AOlder than 1315, 

1316. 

6 Same as site 1316--

6/6 

N? 

N 305 36 24 9 250 ------------------------

20 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

K-Arage 

(Ma) 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

sne No. 

23'1:7 

2331 

2331A 

3235 

3236C 

3503 

4534 

3503A 

3502 

4533 

3503B 

3502A 

3501 

3504 

3504A 

3512 

4522A 

4522B 

4526A 

4535 

4536A 

2405A 

3429 

2406 

Rock type 

or vent No. 

2327 

2331 

2329 

3235 

3236C 

Dacite 

Dacite 

Dacite 

Rhyolite 

Dacite 

Andesite 

Andesite 

Dacite 

Dacite 

Andesite 

Rhyolite 

Rhyolite 

Dacite 

Dacite 

Andesite 

Andesite 

Rhyolite 

Rhyolite 

Dacite 

3335A Rhyolite 

3432 

3433B 

3604 

3425 

4213 

Rhyolite 

Rhyolite 

Rhyolite 

Rhyolite 

Andesite 

Feature 

Vent 

Vent 

Vent 

Vent 

Vent 

Dome 

Dome 

Dome 

Flow 

Flow 

Flow 

Flow 

Flow 

Dome 

Flow 

Dome 

Dome 

Dome 

Dome 

Flow 

Flow 

Dome 

Dome 

Dome 

Dome 

Dome 

Dome 

Dome 

Dome 

Flow 

Location Mean remanent magnetism 

Map 

sheet Lat N. 

( 0) 

sw 

sw 

sw 

sw 

sw 

35.26 

35.24 

35.25 

35.32 

35.32 

NavfNt 

(or Nt) Polarity 

AFD 

(Oe) 

PRE-MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Pre-Matuyama or Matuyama-Continued 

11206 

111.12 

112.11 

11214 

11214 

7/8 

5/8 

6/6 

516 

6/6 

N 

R 

N 

N 

N 

23 45 

206 -42 

7 53 

3 72 

25 64 

MATUYAMA ROCKS 

SILICIC AND INTERMEDIATE ROCKS 

Kendrick Peak rocks, dated 

2 625 250 

23 12 NRM 

5 210 250 

5 196 250 

5 163 250 

c 35.40 111.85 6 R? 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

35.42 

35.41 

35.41 

35.43 

35.41 

35.40 

35.40 

35.40 

35.40 

35.39 

35.45 

35.45 

35.43 

35.42 

35.42 

35.32 

3534 

111.85 

111.85 

111.84 

111.83 

111.85 

111.84 

111.81 

111.87 

111.87 

111.82 

111.85 

111.85 

111.83 

111.82 

111.82 

111.98 

111.99 

4/6 

6 

5n 

7/8 

4/6 

10 

R 

R? 

R 

R 

R 

N? 

165 -33 

176 -39 

219 -23 

250 -51 

Kendrick Peak rocks, undated 

4/6 

6 

6/6 

6/6 

5/6 

6 

4/6 

5!6 

5/6 

R 

R? 

R 

R 

R 

R? 

R 

R 

R 

105 -77 

203 -57 

167 -46 

139 -46 

176 -51 

214 -70 

217 -59 

Sitgreaves Mountain rocks, dated 

R 

R 

173 -56 

159 -60 

Sitgreaves Mountain rocks, undated 

24 

30 

14 

37 

13 

17 

11 

26 

23 

37 

13 

16 

7 

20 

7 

49 

16 

36 

10 

17 

5 

38 

500 

750 

1000 

500 

250 

500 

250 

250 

500 

250 

250 

3 663 NRM 

11 29 250 

Field relations 

Older than 2335A -

K-Arage 

(Ma) 

Older than rhyolite 2.37±0.21 

3502 

Older than 3509---

Younger than dacite 3503, andesite 4536. 

Younger than rhyolite (unsampled, 

270±0.05 Ma). 

Older than 3511----

Older than tmchyte 

4424. 

Older than 3511----

0lder than 4522----

0lder than 4527----

Older than 4535 ----

Older than rhyolite 

3502, 45'1:7, 

4535;younger 

than dacite 4534. 

Same as site 4535 --

209±0.12 

206±0.07 

1.90±0.25 

1.79±0.03 

1.64:!:0.11 

1.35±0.05 

Older than 2405---- 226±0.10 

Older than 3430; 1.90±0.12 

younger than 

rhyolite 3335A 

sw 35.32 112.01 6/6 N 5 56 3 456 250 Younger than rhyolite 2405A. 

sw 35.33 112.04 

c 

c 

35.33 

35.33 

111.98 

111.96 

c 35.40 111.77 

c 35.34 111.91 

sw 35.46 11214 

6/8 

6/6 

6/6 

R? 

R 

R 

177 -54 

259 -55 

7 

21 

87 NRM 

11 500 

Older than rhyolite 

3429,3433. 

Same as site 3335A 

Younger than rhyolite3433A 

Miscellaneous rocks, dated 

4/6 

6/6 

6/6 

R 

R 

R 

176 -69 14 42 

239 -22 6 120 

168 -52 11 37 

500 Older than 3616---- 215:!:0.13 

250 Older than 3529---- 210::!:0.03 

500 Younger than 206±0.18 

4226A, 4332A? 

Table 4 21 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

4510 

3616A 

0603A 

4502 

3531A 

Rock type 

or vent No. 

Rhyolite 

Rhyolite 

Dacite 

Rhyolite 

Rhyolite 

Feature 

Dome 

Dome 

Dome 

Dome 

Dome 

2629 Benmoreite Flow 

2525 Benmoreite Flow 

4424 Trachyte Flow 

3505C Tmchyte Flow 

3435 Benmoreite Dome 

3423A Benmoreite Dome 

2530 Benmoreite Dome 

2529 Benmoreite Dome 

1305A 

2506 

2506A 

3401A 

4435B 

2405 

6835 

Dacite 

Dacite 

Dacite 

Andesite 

Andesite 

2405 

Basalt 

5810A Basalt 

2416 2416 

1230 

3611 

3531 

2420 

6609 

1219 

3611 

2506 

2420 

6609 

6609A 6609 

6617 6609 

6621 6609 

6622 6609 

7727 6609 

6811 6811 

Dome 

Dome 

Dome 

Dome 

Dome 

Vent 

Flow 

Flow 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Flow 

Flow 

Flow 

Flow 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

sw 

c 

c 

c 

c 

LocatiOn Mean remanent magnetism 

Polarity 

MATUYAMA ROCKS-Continued 

SILICIC AND INTERMEDIATE ROCKS-Continued 

Miscellaneous rocks, dated-Continued 

35.48 

35.38 

35.19 

35.49 

35.32 

111.83 

111.76 

111.75 

111.85 

111.90 

35.26 111.78 

35.26 111.80 

35.45 111.91 

35.40 111.88 

35.33 111.92 

35.35 111.93 

35.27 111.90 

35.25 

35.23 

35.32 

35.32 

35.41 

35.40 

111.88 

112.11 

111.90 

111.90 

111.88 

111.95 

6/6 

6 

6/6 

4/6 

4/6 

6 

4/6 

6/6 

4/6 

6!6 

•6 

6/6 

6/6 

R 

R? 

R 

R 

R 

R? 

R 

R 

R? 

R 

R? 

R 

R 

175 -48 

192 -19 

150 -49 

197 -50 

5 

4 

33 

10 

153 

307 

9 

94 

185 -43 12 56 

263 -43 13 28 

160 -58 4 324 

191 -13 10 50 

154 -42 2 813 

Miscellaneous rocks, undated 

6/6 

5/6 

5/6 

5/6 

6 

N 

R 

R 

R 

R? 

350 4 

192 -41 

189 -31 

214 -68 

BASALTIC ROCKS 

Dated 

17 16 

4 350 

13 33 

28 8 

AFD 

(Oe) 

250 

250 

250 

250 

Field relations 

Younger than 

0610. 

K-Arage 

(Ma) 

1.90:!:0.35 

1.64±0.11 

1.61±0.05 

1.54:!:0.02 

1.39±0.06, 

1.29:!:0.23 

Older than 2620, 1.29:!:0.15 

Oak Creek fault; 

younger than 

2630, 2630A. 

500 Same as site 2629 --

500 Older than 4414, 1.14±0.17 

4507,4508, 4517, 

4521;~nger 

than andesite 

3504A. 

Same as site 4424 --

250 Older than 3521---- 1.08:!:0.28 

Older than 3426---- 0.96:!:0.94 

250 Older than 3534; 0.95±0.08 

younger than 

2519B, 2530A. 

250 Same as site 2530 --

250 

250 

250 

250 

Same as site 3531 --

Same as site 3531 --

Older than 4435A -

Same as site 

3401A. 

c 35.32 111.99 6/6 R 170 -52 2 1244 250 Younger than rhyo- 246±0.11 

SP 

SP 

c 

sw 

c 

c 

c 

NW 

35.60 111.52 

35.56 111.52 

35.29 111.96 

35.17 

35.39 

35.32 

35.27 

35.65 

112.23 

111.73 

111.90 

111.99 

111.75 

SP 35.65 111.75 

NW 35.64 111.77 

SP 35.62 111.75 

SP 35.62 111.74 

SP 35.69 111.75 

SP 35.65 111.51 

6/6 

6/6 

6n 

5/6 

4/8 

6/6 

8/8 

5/6 

6/6 

3/6 

2 

6 

6 

6/6 

R 

R 

R 

R 

N 

R 

R 

R 

R 

R 

R? 

N? 

R? 

R 

lite 2405A. 

164 -47 15 22 500 Older than basalt 243±0.32 

144 -75 26 

180 -22 18 

167 -49 

358 60 

195 -34 

214 -60 

196 -43 

5 

5 

5 

20 

4 

8 

16 

272 

308 

156 

9 

405 

191 -46 14 24 

252 -42 36 13 

196 -65 34 5 

5810. 

660 Same as site 6835 --

250 Older than 3433; 

younger than 

2415, 2421A. 

250 

250 

250 

250 

250 

Younger than 

1233. 

Older than 2418, 

3433;younger 

than 2407, 2429, 

2430. 

330 Same as site 6609 --

750 Same as site 6609 --

Same as site 6609 --

Same as site 6609?-

Same as site 6609 --

750 

208±0.48 

201±0.22 

1.44±0.03 

1.41±0.13 

1.38±0.16, 

1.04±0.04 

1.20:!:0.05 

22 Magnetostratigraphy of the ~an Francisco Volcanic Field, Arizona 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

0614 

3433 

nn 

3335 

1

4007 

6804 

6803A 

6803B 

1

4003 

6603 

2519 

2415 

3509 

0603 

2418 

3325 

3511 

4412 

4517 

4520 

5822 

5828 

6817 

0602 

0611 

0611A 

0614A 

Rock type 

or vent No. 

0614 

3433 

Basalt 

3335 

Basalt 

6736 

Basalt 

Basalt 

Basalt 

Basalt 

2519 

2415 

3509 

0603 

2418 

3430 

3511 

4507 

4508 

4517 

Basalt 

Basalt 

5806 

0610 

0611 

0611A 

0615 

Feature 

Vent 

Vent 

Flow 

Vent 

Flow 

Flow 

Flow 

Flow 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Flow 

Flow 

Flow 

Flow 

Vent 

Vent 

Flow 

Map 

sheet 

Location Mean remanent magnetism 

Polarity 

AFD 

(Oe) Field relations 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Dated -Continued 

c 

c 

SP 

sw 

E 

SP 

SP 

SP 

E 

SP 

c 

35.12 

35.32 

35.70 

35.32 

35.47 

35.66 

35.67 

35.66 

35.49 

35.66 

35.28 

111.'13 

111.98 

111.61 

112.05 

111.37 

111.54 

111.53 

111.52 

111.32 

111.62 

111.91 

c 35.29 111.95 

c 35.40 111.87 

c 35.19 111.75 

sw 35.29 11201 

sw 35.34 11202 

c 

c 

c 

c 

SP 

SP 

SP 

c 

c 

c 

c 

35.38 111.82 

35.47 111.92 

35.46 111.88 

35.46 111.88 

35.53 111.52 

35.52 111.54 

35.63 111.57 

35.14 

35.13 

35.13 

35.12 

111.74 

111.72 

111.73 

111.75 

5/6 

7/7 

6/6 

7/7 

5/6 

6/6 

6/6 

6/6 

6/6 

7/7 

7/7 

R 

R 

R 

R 

R 

N 

N 

N 

N 

R 

R 

198 

165 

164 

189 

200 

348 

321 

9 

348 

182 

203 

-27 

-59 

-53 

-54 

-33 

33 

8 

34 

35 

-37 

-70 

11 

7 

21 

8 

24 

29 

29 

29 

14 

18 

24 

51 

77 

11 

60 

17 

6 

8 

6 

30 

11 

7 

500 

250 

750 

250 

500 

330 

500 

330 

500 

330 

250 

Younger than Oak 

Creek fault. 

Older than 2407, 

2408, 2416; 

younger than 

rhyolite 2405A, 

2420, rhyolite 

3433A. 

Older than basalt 

7806, basalt 

77'13A. 

Younger than 

2303, '1308. 

Same as site 

6803A. 

Older than 3018----

Older than 3521; 

younger than 

2424, 2519A, 

2530. 

Dated by field relations 

6/6 

6/6 

6/6 

5/6 

6/6 

6/6 

7/8 

4/6 

8/9 

6/6 

6/6 

6/6 

6/6 

6/6 

6 

6/6 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

R 

R 

N 

Undated 

R 

R 

N? 

R 

178 -28 4 278 

170 -35 12 30 

175 -25 6 117 

163 -49 5 207 

134 -58 28 7 

250 Older than 2416----

250 Younger than dacite 3503A. 

500 Same as dacite 

0603A. 

250 Younger than 

2407,2420. 

250 Younger than rhyolite 4510. 

Younger than andesite 3502A, 

rhyolite 3512A. 

158 -54 2 800 250 Younger than trachyte 4424. 

147 -34 11 70 1000 Younger than trachyte 4424. 

164 -52 5 133 250 Older than 4521; 

younger than 

trachyte 4424. 

212 -70 38 4 750 Older than rhyolite 

(unsampled, 

0.80±0.11 Ma).2 

170 -40 16 19 330 Same as site 5822--

350 58 10 45 500 Older than 6736; 

244 

209 

129 

-20 

-29 

-55 

14 

17 

14 

25 

16 

24 

1000 

1000 

750 

younger than 

basalt6803A. 

Older than 0603 ----

Younger than rim 

basalt (unsampled). 

K-Ar age 

(Ma) 

1.16±0.04 

1.15±0.65 

1.09±0.03 

1.07±0.06 

1.07±0.15 

1.04±0.14 

1.01±0.13 

0.85±0.12 

0.83±0.04 

0.69±0.13 

Table 4 23 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Location Mean remanent magnetism 

sne No. 

1301 

1403 

1403A 

1413 

1414 

1414A 

1419 

1430 

1505B 

1615 

1617 

1618 

1622 

1622A 

1628 

1636 

2203 

2212 

2301 

2301A 

2308 

2308A 

2315 

2316 

2316A 

2317 

2324 

2325 

2335A 

2407 

2408 

2409 

2415A 

2421 

Rock type 

or vent No. 

1407 

Basalt 

Basalt 

Basalt 

Basalt 

Basalt 

1419 

1430 

1505A 

1615 

1617 

1618 

1622 

1621 

1628 

1625 

2203 

2212 

2301 

2301A 

2308 

2308A 

2315 

2316 

2316A 

2317 

2324 

2325 

2335A 

2407 

2408 

2416A 

2415A 

2421 

Feature 

Flow 

Flow 

Flow 

Flow 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Map 

sheet 

sw 

c 

c 

c 

c 

c 

sw 

sw 

c 

c 

c 

c 

c 

c 

c 

c 

sw 

35.23 

35.23 

35.22 

35.19 

35.20 

35.20 

35.16 

35.17 

35.23 

35.21 

35.20 

35.20 

35.19 

35.19 

35.18 

35.16 

35.32 

sw 35.30 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

c 

c 

c 

c 

35.32 

35.32 

35.30 

35.31 

35.29 

35.29 

35.28 

35.29 

35.27 

35.26 

35.24 

35.30 

35.30 

35.29 

35.28 

35.27 

Polarity 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

112.03 

111.% 

111.95 

111.93 

111.94 

111.93 

112.01 

112.01 

111.88 

111.75 

111.78 

111.80 

111.74 

111.75 

111.77 

111.71 

112.17 

112.16 

112.02 

112.03 

112.11 

112.09 

112.06 

112.07 

112.08 

112.11 

112.03 

112.01 

112.04 

112.00 

111.98 

111.96 

111.96 

111.97 

517 

6/6 

4/6 

6 

4/6 

12/13 

6/6 

6/6 

3/7 

517 

7 

3/9 

6/6 

6/6 

5/8 

5!6 

7/7 

4/6 

6 

5/6 

8/9 

8/9 

5/6 

5/8 

8/9 

8 

6/6 

7 

5!6 

7/7 

6/6 

8/8 

6/6 

6/6 

R 

R 

R 

R? 

R 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

N 

N 

R 

N? 

R 

R? 

R 

R 

R 

R 

R 

R 

190 -n 

190 -56 

255 -57 

156 -25 

173 -50 

219 -22 

153 -66 

181 -46 

183 -40 

193 -35 

142 -55 

165 -59 

206 -57 

168 -67 

181 -42 

178 -52 

152 -12 

182 -57 

190 -43 

333 31 

284 48 

184 -54 

165 -52 

154 -63 

145 -67 

175 -56 

184 -54 

166 -58 

174 -31 

24 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

35 

13 

21 

18 

5 

4 

2 

18 

7 

13 

22 

2 

10 

9 

4 

AFD 

(Oe) 

6 1000 

26 500 

21 250 

27 500 

75 250 

287 500 

1220 250 

50 250 

138 NRM 

92 750 

10 750 

1297 250 

63 NRM 

74 750 

266 NRM 

Field relations 

Older than 2335A, 

2420, 3521; 

younger than 

1419. 

Same as site 1403 --

Same as site 1403--

Same as site 1403 --

Same as site 1403 --

Older than 1407----

Older than 1520----

Younger than 

1505/1506/ 

1508/2436. 

Older than 1602----

Younger than rim 

basalt (unsampled). 

Younger than rim 

basalt (unsampled). 

Older than 1602, 

1625, Oak Creek 

fault; younger 

than rim basalt 

(unsampled, 

6.01±0.50 Ma). 

Younger than rim 

basalt (unsampled). 

Younger than 

1622. 

Younger than 

2220. 

2 1864 NRM Younger than 

7 116 

3 387 

22 7 

8 104 

38 5 

8 44 

7 82 

16 24 

6 93 

33 5 

8 51 

5 193 

4 330 

250 

250 

250 

250 

500 

250 

250 

1000 

250 

250 

250 

250 

250 

2215. 

Younger than 

2308,2320. 

Younger than 

2320. 

Older than 2420, 

2325A. 

Younger than 

1311, 1407, 2327, 

2335. 

Older than 2418, 

2420,3433. 

Older than 3433----

0lder than 3433 ----

K-Arage 

(Ma) 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

2424 

2425 

2425A 

2429 

2430 

2509 

2517 

2517A 

2522 

2530A 

2531 

2531A 

2533 

2525A 

3202 

3218 

3220 

3221 

3226 

3226A 

3229 

3236 

3236A 

3236B 

3301 

3305 

3306 

3306A 

3310 

3311 

3323 

3324 

3326 

Rock type 

or vent No. 

2423 

2424 

2530 

2429 

2430 

2509 

2517 

2517A 

2522 

2530A 

2531 

2531A 

2533 

2630 

2604 

Basalt 

Basalt 

Basalt 

3202 

3113 

3229 

3221 

3226 

3226A 

3230 

3236 

3331 

3236B 

3301 

3305 

3306 

3306A 

3310 

3311 

3325A 

3324 

3325 

Feature 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Flow 

Map 

sheet 

c 

c 

c 

c 

sw 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

E 

E 

E 

Location 

NaviNt 

(or Nt) 

Mean remanent magnetism 

Polarity 

AFD 

(Oe) Field relations 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

35.28 

35.27 

35.27 

35.26 

35.26 

35.30 

35.28 

35.28 

35.27 

35.27 

35.24 

35.24 

35.24 

35.26 

111.93 

111.92 

111.92 

111.95 

112.Ql 

111.88 

111.89 

111.88 

111.85 

111.90 

111.90 

111.91 

111.87 

111.80 

35.31 111.77 

35.37 111.20 

35.42 11130 

3539 111.30 

6/6 

5n 

6/6 

1n 

1n 

6/6 

5n 

6!6 

4!6 

6/6 

8!9 

4/6 

5/6 

6n 

5 

4/6 

5/6 

5/6 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

162 -27 

224 -50 

187 -27 

170 -58 

140 -62 

201 -4 

144 -31 

177 -47 

209 -60 

187 -24 

164 -45 

153 -50 

206 -55 

191 -49 

7 63 250 

33 7 NRM 

9 58 250 

5 140 250 

6 113 250 

16 18 500 

24 11 250 

2 1750 250 

22 18 500 

13 27 250 

12 22 250 

10 82 250 

8 85 NRM 

4 229 250 

Older than 2519, 

3521. 

Older than 2519----

0lder than 2519----

0lder than 2420, 

3521. 

Older than 2420----

Older than basalt 

2616. 

Older than basalt 

2616. 

Older than benmoreite 2530. 

Younger than 

1505/1506/ 

1508/2436. 

Older than 3534----

Older than benmoreite 2629. 

168 -77 20 22 500 Same as site 3002 --

140 -65 26 10 500 Older than 3018----

148 -79 14 31 500 Same as basalt 

3002 

sw 35.40 112.16 6 R? Younger than 

3229,3307. 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

SW 

sw 

sw 

35.37 

35.35 

3536 

35.34 

35.34 

35.34 

35.33 

35.33 

3533 

35.40 

35.40 

112.23 

112.20 

11219 

112.16 

112.14 

112.21 

112.13 

112.12 

112.13 

112.02 

112.09 

sw 35.40 112.11 

sw 

sw 

sw 

SW 

sw 

sw 

35.40 

35.39 

3539 

35.36 

3536 

35.35 

11212 

112.06 

112.04 

112.05 

112.03 

112.04 

6/6 

6/6 

5/6 

6n 

4/6 

8/8 

5!6 

4/6 

5!6 

6/6 

5!6 

6 

6/8 

5/8 

6/6 

6!6 

5/6 

6/6 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

R 

R 

R 

156 -50 

183 -55 

187 -43 

193 -48 

178 -54 

177 -60 

176 -56 

185 -29 

183 -54 

187 -58 

154 -47 

181 

208 

171 

176 

178 

204 

-48 

-67 

-56 

-6 

-33 

-63 

6 147 

7 105 

9 74 

7 87 

6 208 

3 439 

15 28 

4 436 

3 602 

6 148 

24 11 

4 

4 

8 

24 

5 

3 

280 

411 

76 

9 

270 

458 

250 

250 

250 

250 

250 

250 

250 

250 

500 

250 

750 

500 

500 

250 

750 

500 

250 

Older than 3229; 

younger than 

3136. 

Older than 3202, 

3221;younger 

than 2220,3113. 

Younger than 

3229. 

Same as site 3331--

Older than 3310; 

younger than 

3306. 

Older than 3305; 

younger than 

3307. 

Younger than 

4236. 

Younger than 

3305, 3306?' 

3407, 4332A. 

Older than 3407? --

Younger than 

3407. 

K-Ar age 

(Ma) 

Table 4 25 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

3327 

3331 

3401 

3404 

3406 

3407 

3416 

3417 

3423 

3424 

3505 

3505A 

3505E 

3508 

3509A 

3517 

3517A 

3518 

3528 

1

4023 

4226 

4301 

4302 

4303 

4311 

4311A 

4314 

4323 

4324 

4324A 

4324B 

4326 

4327 

4335 

4336 

4405 

4409 

4413 

Rock type 

or vent No. 

3327 

3331 

3401 

3404 

3406 

3407 

3416 

3417 

3423 

3424 

3505 

3505A 

3508 

3508A 

3509A 

3517 

3518 

3507 

3528 

Basalt 

4226 

4301 

4302 

4303 

4311 

4311A 

4314 

4323 

4324 

4313 

4323C 

4326 

4327 

4325 

4336 

4405 

4409 

4413 

Feature 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Map 

sheet 

sw 

sw 

c 

c 

sw 

sw 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

E 

sw 

sw 

sw 

sw 

sw 

sw 

SW 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

c 

c 

c 

Location Mean remanent magnetism 

35.35 

3533 

35.41 

35.41 

35.40 

35.39 

3537 

35.37 

35.36 

35.35 

35.40 

35.40 

35.40 

35.38 

35.39 

35.38 

3537 

35.38 

35.35 

35.46 

35.44 

35.47 

35.48 

35.49 

35.49 

35.47 

35.46 

35.45 

35.45 

35.45 

35.45 

35.44 

35.44 

35.42 

35.41 

35.49 

35.47 

35.46 

Polarity 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

112.06 

112.13 

111.92 

111.98 

11200 

11201 

111.97 

111.99 

111.94 

111.92 

111.90 

111.90 

111.90 

111.88 

111.88 

111.88 

111.88 

111.90 

111.87 

11130 

11216 

11203 

11204 

11206 

11204 

112.05 

11209 

112.05 

112.03 

11202 

11203 

112.04 

112.06 

112.04 

112.02 

111.98 

111.98 

111.92 

6/6 

6/6 

4/6 

6/6 

5/6 

,6/6 

6/6 

1n 

6/6 

5/6 

6/6 

6/6 

6/6 

6/6 

6/6 

5/6 

5/6 

5/6 

5/6 

5/6 

6/6 

9/9 

5/6 

6/6 

6/10 

5!5 

6/8 

5/6 

6/6 

6/6 

5/6 

3/6 

5/8 

5/6 

6/6 

5/6 

9/9 

5/6 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

N 

200 -46 

177 -26 

210 -54 

164 -61 

162 -46 

165 -60 

217 -51 

144 -46 

170 -47 

175 -42 

174 -43 

175 -38 

172 -47 

242 -49 

189 -45 

174 -42 

170 -37 

140 -67 

218 -38 

171 -46 

193 -59 

178 -52 

179 -54 

152 -51 

219 -45 

154 -52 

158 -61 

167 -51 

122 -40 

162 -73 

202 -50 

181 -45 

153 -49 

183 -41 

187 -63 

173 -25 

175 -53 

332 59 

2 

2 

6 

2 

14 

5 

10 

9 

4 

10 

5 

8 

22 

18 

28 

14 

21 

5 

33 

21 

7 

4 

3 

9 

11 

5 

8 

27 

8 

20 

5 

5 

25 

11 

13 

26 

12 

9 

26 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

AFD 

(De) 

1400 250 

1201 500 

204 250 

984 250 

31 500 

200 250 

49 250 

45 250 

239 250 

58 250 

164 250 

69 250 

10 250 

15 250 

7 250 

30 250 

14 250 

240 250 

6 250 

15 500 

87 250 

169 250 

608 250 

54 750 

40 250 

271 750 

75 250 

9 750 

75 250 

12 500 

202 250 

563 250 

10 250 

54 250 

29 1000 

9 250 

19 250 

72 250 

Field relations 

Younger than 

2303. 

Older than 4435A -

Older than 3310?, 

3325A, 4325; 

younger than 

3301, 3311, 4430. 

Older than 3420----

0lder than 3518----

0lder than 3426----

Younger than 

3509A. 

Older than 3508A -

Older than 3522, 

3523. 

Older than 3523, 

3529, 3608; 

younger than 

3423. 

Older than 3523----

Same as site 3002 --

Younger than 

4236. 

Older than 4408, 

4425, 5430; 

younger than 

4311. 

Older tb.'\0 4301----

0lder than 5335 ----

Older than 4425; 

younger than 

4323A. 

Older than 4326----

0lder tb.'\0 4323C, 

4425. 

Younger than 

4324. 

Younger than 

4323. 

Younger than 

4332A? 

Younger than 

3407. 

Older tb.'\0 4435A -

Older tb.'\0 trachyte 

4424? 

K-Ar age 

(Ma) 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

4416 

4417 

4417A 

4417B 

4418 

4418A 

4418B 

4419 

4427 

4427A 

4428 

4429 

4429A 

4432 

4432A 

4435 

4435A 

4436 

4506 

4522 

4526 

4527 

1

5033 

5309 

5310 

5321 

5334 

5334A 

5335 

5411 

5413 

5415 

5416 

5419 

5421 

5431 

5431A 

5432 

5432A 

5432B 

Rock type 

or vent No. 

4416 

4417 

4417A 

4418A 

4418 

4418B 

4418C 

4419 

4427 

4427A 

4432 

4429 

4429A 

4432 

4432A 

4435 

4435A 

4436 

4506 

4522 

4526 

4527 

Basalt 

5309 

5310 

5321 

5334 

5335 

5335A 

5411 

5413 

5415 

5416 

5419 

5422 

5431 

5430 

5432 

5432A 

5432B 

Feature 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Yent 

Vent 

Vent 

Vent 

Vent 

Map 

sheet 

c 

c 

c 

c 

sw 

sw 

sw 

sw 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

E 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

Location Mean remanent magnetism 

35.46 

35.47 

35.44 

35.46 

35.46 

35.46 

35.47 

35.45 

35.43 

35.43 

35.43 

35.43 

35.44 

35.42 

35.42 

35.43 

35.41 

35.42 

35.49 

35.44 

35.44 

35.43 

35.50 

35.56 

35.56 

35.53 

35.51 

35.51 

35.51 

35.56 

35.54 

35.54 

35.54 

35.53 

35.53 

35.51 

35.51 

35.51 

35.50 

35.51 

NavfNt 

(or Nt) Polarity 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

111.98 

111.99 

11200 

112.00 

112.01 

112.00 

112.01 

112.01 

111.96 

111.96 

111.97 

111.99 

111.99 

111.99 

11200 

111.94 

111.94 

111.92 

111.90 

111.85 

111.84 

111.84 

111.33 

112.07 

112.07 

112.07 

112.05 

112.05 

112.04 

111.94 

111.92 

111.94 

111.97 

112.00 

111.96 

112.00 

11200 

112.00 

111.98 

111.98 

5!6 

7!7 

6/6 

6/6 

6!6 

5/6 

6/6 

4/6 

6!6 

5!6 

7/8 

6!6 

6/6 

5!6 

6/6 

4/6 

6!6 

4/5 

6!9 

6 

6 

6/6 

5!6 

6/6 

5/6 

6 

4/6 

5/6 

5/6 

6/8 

4/4 

7/9 

4/7 

6/6 

6 

5/6 

5/6 

5/6 

6/6 

5!6 

R 

R 

R 

R 

R 

R 

R 

N 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R? 

R? 

R 

N 

R 

R 

N? 

N 

N 

R 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

R 

R 

172 

184 

147 

123 

196 

149 

140 

355 

167 

150 

173 

196 

167 

164 

175 

179 

175 

182 

193 

187 

339 

218 

213 

36 

24 

190 

150 

228 

148 

158 

163 

153 

200 

161 

210 

222 

-49 

-57 

-45 

-49 

-39 

-44 

-46 

40 

-64 

-70 

-45 

-50 

-3 

-57 

-50 

-48 

-11 

-32 

-45 

-45 

41 

-28 

-51 

61 

59 

-51 

-64 

-69 

-62 

-54 

-56 

-64 

-41 

-49 

-55 

-53 

17 

5 

3 

11 

33 

7 

15 

15 

17 

10 

13 

2 

5 

13 

19 

25 

14 

14 

15 

8 

25 

12 

6 

4 

7 

2 

8 

11 

18 

11 

6 

6 

8 

7 

8 

7 

AFD 

(Oe) 

22 500 

173 250 

667 500 

40 250 

5 500 

110 500 

22 1000 

41 250 

16 250 

58 250 

22 250 

872 250 

200 250 

35 250 

14 250 

15 NRM 

23 NRM 

42 NRM 

22 250 

68 250 

10 500 

35 500 

153 250 

563 1000 

139 250 

1447 250 

72 250 

66 1000 

13 250 

67 250 

114 250 

193 500 

78 250 

111 250 

79 250 

130 250 

Field relations 

Younger than 

4418B. 

Older than 4419----

0lder than 4418A; 

younger than 

4418C. 

Older than 4418B--

Younger than andesite 4418. 

Older than 4425 ----

Same as site 4432 --

Younger than 

4430. 

Older than 4425; 

younger than 

3401, andesite 

3401A, 4405, 

5422, 5434. 

Younger than rhyolite 4522A. 

Older than 4521; 

younger than 

dacite 4522B?, 

andesite 4536A. 

Older than 3018----

Younger than 

4311A. 

Older than 5413, 

5529; younger 

than 5416,6422 

Older than 5529; 

younger than 

5411. 

Older than 5411----

Older than 4435A -

Younger than 

4301. 

K-Ar age 

(Ma) 

Table 4 27 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

5432C 

5434 

5525 

5526 

5836 

6403 

6409 

6412 

6413 

6414 

6422 

6604 

6604A 

6604B 

6618 

6619 

6619A 

6621A 

6733 

6802 

6803 

7408 

7417 

7421 

7433 

0502 

0617 

1201 

1212 

1214 

1215 

1225 

1305 

1318 

1630 

Rock type 

or vent No. 

5432A 

5434 

5630 

5526 

Basalt 

Basalt 

6403 

6409 

6412 

6413 

6414 

6422 

6604 

6604 

6604 

6618 

6619 

6619A 

Basalt 

5704 

6802 

6803 

7408 

7417 

7421 

7433 

0502 

0608 

1201 

1212 

1223A 

1215 

1224A 

1305 

1305 

1629 

Feature 

Flow 

Vent 

Flow 

Vent 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow· 

Vent 

Map 

sheet 

NW 

NW 

NW 

NW 

SP 

E 

NW 

NW 

NW 

NW 

NW 

NW 

NW 

SP 

SP 

NW 

NW 

NW 

SP 

SP 

SP 

SP 

NW 

NW 

NW 

NW 

c 

c 

sw 

sw 

SW 

sw 

SW 

sw 

sw 

c 

Location Mean remanent magnetism 

35.51 

35.51 

35.52 

35.52 

Nav/Nt 

(or Nt) Polarity 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

111.98 

111.95 

111.80 

111.83 

4/6 

5/6 

4/6 

R 

R 

R 

212 -50 

233 -47 

89 -83 

217 -46 

35.50 111.50 

6/6 

6 

R 

R? 

35.50 111.46 

35.67 

35.65 

35.65 

35.64 

35.64 

35.62 

35.66 

35.66 

35.67 

35.64 

35.62 

35.62 

35.61 

35.60 

35.66 

35.66 

35.74 

35.73 

35.71 

35.68 

35.14 

35.11 

35.23 

35.22 

35.19 

35.20 

35.19 

35.22 

35.21 

35.19 

111.96 

111.97 

111.92 

111.91 

111.92 

111.96 

111.75 

111.75 

111.75 

111.78 

111.80 

111.80 

111.75 

111.65 

111.50 

111.53 

111.98 

111.98 

111.97 

111.94 

111.84 

111.79 

112.13 

112.13 

112.15 

112.16 

112.14 

112.11 

112.11 

111.79 

7 

6/6 

4/6 

6/6 

4/6 

5/6 

6/6 

5/6 

8/8 

4/6 

5!6 

3/6 

5/6 

7/7 

6/6 

8/8 

7/8 

6 

6/6 

5/6 

5/6 

N? 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R? 

R 

R 

R 

161 -59 

130 -49 

186 -55 

238 -45 

174 -60 

156 -58 

186 -75 

197 -51 

222 -49 

206 -74 

168 -44 

205 -65 

196 -45 

208 -32 

149 -40 

153 -75 

198 -58 

166 -57 

128 -60 

Matuyama or pre-Matuyama 

5/6 

4/6 

5!6 

6/6 

5/5 

6/6 

6/6 

3/6 

5/6 

7/8 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

187 -60 

215 -35 

220 -65 

130 -50 

148 -45 

193 -60 

226 -45 

121 -59 

182 -34 

190 -44 

11 67 

3 680 

19 24 

6 113 

AFD 

(Oe) 

1000 

250 

1000 

250 

2 992 250 

13 52 500 

5 176 250 

37 7 750 

8 97 500 

2 1295 250 

19 16 250 

4 233 330 

3 1145 500 

14 29 1000 

24 28 1000 

13 35 500 

13 23 330 

37 4 330 

6 95 330 

39 3 500 

2 728 250 

2 1048 250 

9 66 500 

4 

23 

5 

13 

4 

2 

4 

6 

16 

11 

301 

17 

232 

29 

315 

872 

228 

472 

23 

29 

250 

500 

250 

250 

250 

250 

250 

500 

500 

250 

28 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

Field relations 

Same as site 

5432A. 

Older than 4435A -

Older than 5535, 

4606/5536. 

Older than rhyolite 

(unsampled, 

0.80±0.11 MaV1 

Older thnn andesite 

3707 A, 5703, 

rhyolite (onsampled, 

0.80±0.11 Ma).2 

Older than 6422----

Older than 5411; 

younger than 

6409. 

Same as site 6604 --

Same as site 6604 --

Older than 6609----

Younger than rim 

basalt (unsampled). 

Older than 1305?; 

younger than 

1226. 

Older than 2332; 

younger than 

1224A?, dacite 

1305A. 

Same as site 1305 --

Younger than rim 

basalt (unsampled). 

K-Ar age 

(Ma) 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

1631 

1631A 

2303 

2332 

2335 

2507 

2519A 

2630 

3203 

3212 

3215 

3328 

4226B 

4323A 

4323B 

4326A 

4430 

3420 

Rock type 

or vent No. 

1631 

1525 

2304 

2332 

2335 

2507 

2519A 

2630A 

3203 

3212 

3215 

3328 

4225 

4323A 

4323B 

4326A 

4430 

3420 

3505B 3505B 

3505D 3504 

4311B 

3729 

3614 

2713 

2705 

2601 

2703 

4302A 

Andesite/ 

dacite 

Dacite 

Dacite 

Rhyolite 

Andesite 

Andesite 

Feature 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Section 

Flow 

Dome 

Flow 

Flow 

Flow 

Map 

sheet 

c 

c 

sw 

sw 

sw 

c 

c 

c 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

sw 

c 

c 

c 

sw 

c 

c 

c 

c 

c 

c 

Location Mean remanent magnetism 

35.15 

35.16 

35.32 

35.24 

35.24 

35.30 

35.27 

35.27 

35.41 

35.38 

35.37 

35.34 

35.43 

35.45 

35.44 

35.43 

35.43 

Nav/Nt 

(or Nt) Polarity 

MATUYAMA ROCKS-Continued 

BASALTIC ROCKS-Continued 

Matuyama or pre-Matuyama-Continued 

AFD 

(Oe) Field relations 

111.81 5/6 R 195 -36 13 38 500 Younger than rim 

basalt (unsampled). 

111.81 

112.07 

112.10 

112.04 

111.89 

111.91 

111.79 

112.16 

112.14 

112.17 

112.07 

112.14 

112.04 

112.04 

112.04 

112.01 

6 

6/6 

617 

6/6 

5!6 

517 

5/6 

5/6 

717 

5!6 

5!6 

6!6 

4/6 

517 

5/6 

6/6 

N? 

N 

R 

N 

N 

N 

N 

R 

R 

R 

N 

R 

N 

N 

N 

N 

7 56 

256 -62 

331 62 

342 61 

54 79 

8 50 

152 -47 

187 -58 

173 -61 

333 53 

214 -35 

4 64 

352 61 

291 78 

350 62 

Matuyama or Brunhes 

2 1109 250 

13 28 NRM 

2 1793 250 

10 56 250 

21 15 250 

31 7 500 

13 36 

5 141 

20 16 

4 343 

24 9 

15 38 

8 101 

36 5 

14 23 

500 

250 

250 

250 

500 

250 

250 

750 

250 

Younger than rim 

basalt (unsampled). 

Older than 2335A -

Older than 2519; 

younger than 

2519B. 

Older than benmoreite 2629. 

Older than 4314; 

younger than 

4323. 

Older than 4429----

35.36 112.00 6 N? Younger than 

3417. 

35.40 111.90 6/6 N 352 67 14 23 

35.40 111.88 5/6 N 341 65 5 200 

35.48 

35.34 

35.37 

35.30 

35.32 

35.32 

35.24 

112.04 6/6 N 36 65 

BRUNHES ROCKS 

SILICIC AND INTERMEDIATE ROCKS 

San Francisco Mountain rocks, dated 

111.67 88 N 

111.73 5/5 N 16 11 

111.61 6/6 N 352 43 

111.67 4/6 N 45 66 

111.71 6 N? 

San Francisco Mountain rocks, undated 

5 • 211 

11 50 

3 309 

21 21 

111.64 6/6 N 13 51 12 32 

250 Younger than trachyte 4424. 

500 Younger than andesite 3504A. 

250 

250 Older than andesite 

3729; younger 

than dacite 

3718? 

250 Older than dacite 

2818A; younger 

than andesite 

2703,2818. 

1000 Younger than andesite 2703. 

Older than basalt 

2616. 

500 Older than dacite 

2705; younger 

than rhyolite 

2705. 

K-Ar age 

(Ma) 

0.75±0.07, 

0.43±0.03 

0.75±0.17 

0.75±0.04 

0.70±0.10, 

0.87±0.15 

0.60±0.08 

Table 4 29 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

2704 

2705A 

2732 

2733 

2818A 

3614A 

3707 

3707A 

3711 

3711A 

3711B 

3718 

3829 

4804 

2736 

1807 

2726 

2726A 

3612 

6713 

6818 

6701 

7833 

2616 

3633 

3634 

4623 

5622 

3522 

4536 

Rock type 

or vent No. 

Dacite 

Andesite 

Andesite 

Dacite 

Dacite 

Dacite 

Andesite 

Andesite 

Dacite 

Dacite 

Andesite 

Dacite 

Andesite 

Andesite 

Dacite 

Dacite 

Dacite 

Dacite 

Rhyolite 

6713 

6713 

6713 

Basalt 

Basalt 

3633 

3634 

4624 

4624 

3522 

4536 

Feature 

Dome 

Flow 

Flow 

Pyroclastic 

breccia. 

Flow 

Dome 

Flow 

Flow 

Flow 

Flow 

Flow 

Dome 

Flow 

Flow 

Dome 

Pyroclastic 

breccia. 

Dome 

Dome 

Dome 

Vent 

Flow 

Flow 

Flow 

Flow 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Map 

sheet 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

E 

c 

c 

c 

c 

c 

SP 

SP 

SP 

SP 

c 

c 

c 

c 

SP 

c 

c 

Location Mean remanent magnetism 

35.33 

35.32 

35.24 

35.24 

35.30 

35.38 

35.39 

35.38 

35.40 

35.40 

35.39 

35.37 

35.34 

35.49 

35.23 

35.26 

35.27 

35.26 

35.38 

35.63 

35.63 

35.66 

35.67 

35.29 

35.34 

35.33 

35.45 

35.54 

35.37 

35.42 

Polarity 

BRUNHES ROCKS-Continued 

SILICIC AND INTERMEDIATE ROCKS-Continued 

San Francisco Mountain rocks, undated-Continued 

111.65 

111.67 

111.69 

111.67 

111.58 

111.73 

111.69 

111.69 

111.62 

111.62 

111.61 

111.70 

111.57 

111.54 

111.60 

111.58 

111.61 

111.63 

111.71 

111.60 

111.58 

111.59 

111.55 

111.76 

111.75 

111.74 

111.72 

111.74 

111.86 

111.81 

4/6 

6/8 

4/6 

5/6 

6 

4/6 

4n 

4/6 

4/6 

6/6 

6 

5/6 

6/6 

6/6 

N 

N 

N 

N 

N? 

N 

N 

N 

N 

N 

N? 

N 

N 

N 

309 

5 

3 

341 

354 

14 

19 

5 

2 

347 

72 

38 

Miscellaneous rocks, dated 

5/5 N 2 

MiscelLmeous rocks, undated 

6/6 

6/6 

6/6 

4/6 

N 

N 

N 

N 

339 

299 

302 

12 

BASALTIC ROCKS 

Dated 

9/9 

6/6 

9/9 

8/8 

6 

6 

6/6 

5/6 

6 

6 

6/6 

N 

N 

N 

N 

N? 

N? 

N 

N 

N? 

N? 

N 

358 

347 

354 

340 

326 

15 

344 

35 

70 

14 

56 

49 

49 

58 

72 

41 

39 

40 

45 

5 

17 

23 

11 

8 

18 

30 

10 

8 

7 

17 

8 

0 38 

48 

36 

54 

46 

61 

56 

25 

57 

41 

47 

54 

9 

22 

8 

7 

27 

29 

31 

4 

2 

11 

6 

30 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

362 

17 

17 

51 

145 

26 

10 

89 

69 

123 

16 

80 

5 

63 

10 

65 

196 

5 

6 

4 

169 

904 

47 

112 

AFD 

(Oe) 

250 

250 

500 

250 

250 

500 

500 

500 

250 

250 

750 

250 

Field relations 

Younger than dacite 2726. 

Same as site 2704 --

Younger than dacite 2713. 

Same as site 3718? 

Older than rhyolite 

3612. 

Older than dacite 

3614. 

Older than dacite 

3614, andesite 

3729; younger 

than andesite 

3707. 

Older than 3705?, 

4711,4819. 

K-Arage 

(Ma) 

250 ------------------------ 0.57±0.03, 

250 

250 

250 

250 

330 

330 

750 

330 

250 

250 

250 

Older tlu.m dacite 

2733. 

Same as site 2726 --

Younger than 

3601, andesite 

3707, andesite 

3729. 

Same as site 6713 --

Same as site 6713 --

Same as site 2616--

Same as site 2616 --

Younger th...'ln 

4606/5536,4609. 

Same as site 4623 --

Younger than 

4521,4631, 5535, 

5536. 

0.49±0.06 

o.n±o.04 

0.74±0.08 

0.72±0.12 

0.66±0.11 

0.56±0.08 

0.53±0.08. 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

8833 

1

5033A 

1

4017 

7817 

7735 

2526 

3628 

3631 

2513 

3621 

3621A 

3617 

3616 

Rock type 

or vent No. 

4536 

Basalt 

3018 

Basalt 

Basalt 

2620 

3621/ 

3621A 

3621/ 

3621A 

3621/ 

3621A 

3621 

3621A 

3608 

3616 

3528C 3521 

3534A 3521 

2433 3521 

1417 3521 

1602 

2731 

5831 

5833 

3

4A35 

5703 

6726 

3

6734 

8

1904 

8

4920 

8

3910 

3

3934 

8

3929 

1602 

1602 

5831 

5831 

3034/3036 

5703 

5703 

5703 

2929 

4920 

3824 

2902 

3929 

Feature 

Flow 

Flow 

Flow 

Flow 

Flow 

Flow 

Flow 

Flow 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Flow 

Flow 

Vent 

Flow 

Vent 

Flow 

Flow 

Vent 

Flow 

Flow 

Flow 

Flow 

Flow 

Vent 

Vent 

Map 

sheet 

SP 

E 

E 

SP 

SP 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

SP 

E 

SP 

SP 

SP 

E 

E 

E 

E 

E 

Location 

NaviNt 

(or Nt) 

Mean remanent magnetism 

Polarity 

AFD 

(Oe) Field relations K-Ar age 

(Ma) 

BRUNHES ROCKS-Continued 

BASALTIC ROCKS-Continued 

Dated-Continued 

35.76 

35.50 

35.46 

35.72 

35.68 

35.26 

35.39 

111.54 

111.33 

111.36 

111.56 

111.62 

111.82 

111.75 

35.33 111.78 

35.29 111.81 

35.37 

35.37 

35.39 

111.76 

111.75 

111.78 

35.37 111.77 

35.36 111.86 

35.33 111.85 

35.24 111.% 

35.20 112.00 

35.27 

35.25 

35.50 

35.50 

35.43 

35.58 

35.61 

35.59 

35.24 

111.73 

111.70 

111.58 

111.56 

111.20 

111.63 

111.62 

111.63 

111.44 

35.45 111.46 

35.39 111.43 

35.33 111.42 

35.35 111.46 

8/8 

5/6 

5/6 

6/6 

6/6 

6 

4/5 

17/20 

18/23 

6/6 

6 

6/6 

4/6 

6/6 

5/5 

4/6 

5/6 

5!5 

5/6 

2/2 

6/6 

8/12 

9/9 

9/9 

8/13 

11/12 

6/12 

19/20 

22/24 

21/21 

N 

N 

N 

N 

N 

N? 

N 

N 

N 

N 

N? 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

31 

13 

351 

11 

310 

52 

26 

62 

54 

71 

5 129 

11 46 

9 70 

3 

19 

43 

14 

358 40 22 19 

2 53 5 46 

354 49 10 13 

359 18 24 11 

8 44 10 49 

6 38 19 25 

352 65 19 14 

333 79 16 25 

332 61 8 142 

349 64 6 155 

288 

341 

1 

28 

9 

2 

80 

7 

355 

67 

54 

52 

69 

32 

65 

57 

55 

53 

10 

10 

8 

33 

4 

10 

61 

61 

1087 

5 

189 

19 

15 13 

4 259 

1 1407 

330 Same as site 4536 --

500 Older than 3018 - 0.50±0.09 

500 Younger than ba- 0.49±0.11 

500 

330 

salt 4035, basalt 

5033A. 

Same as basalt 

7817. 

0.46±0.05 

Younger than ba- 0.44±0.18 

salt 2616, benmoreite 2629, 

3534. 

500 Older than 3616, 0.42±0.06 

3619; younger 

than basalt 2616, 

3630. 

250 Same as site 3628 --

250 Same as site 3628 --

250 Same as site 3628 --

Same as site 3628 --

250 Younger than 0.39±0.11 

3518, 3523. 

250 Younger thnn rhyo- 0.35±0.13 

lite 3604, 

3621/3621A. 

250 Younger than 0.34±0.21 

1407, 2423, 2429, 

2519, basalt 

2616, 3523A, 

benmoreite 

3435,3534. 

500 Same as site 

3528C. 

500 Same as site 

3528C. 

500 Same as site 

3528C. 

500 

500 

330 

330 

300 

330 

Younger than 

1615, benmoreite 

1622, 1625. 

Same as site 1602--

Same as site 5831 --

Merriam basaltic 

stage. 

Merriam basaltic 

stage. 

750 Same as site 5703 --

400 Same as site 5703 --

0.33±0.08 

0.22±0.05 

0.15±0.03 

0.071±0.04 

300 Merrinm basaltic 0.055±0.014 

stage. 

358 53 5 213 400 Merriam basaltic 0.051±0.046 

stage. 

354 65 2 406 NRM Sunset basaltic A.D.1065 

stage. 

347 62 3 221 NRM Sunset basaltic 4

A.D.ll00 

stage. 

345 61 2 407 NRM Sunset basaltic 4

A.D.1100 

stage. 

Table 4 31 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. Rock type 

or vent No. 

3824 

3824 

2515 3534 

2521 3534 

2621A 2621A 

3534 3534 

3619 3619 

3619A 3619 

4705 4708 

5718 5718 

Feature 

Flow 

Vent 

Flow 

Flow 

Vent 

Vent 

Vent 

Flow 

Flow 

Flow 

5719 4708 Flow 

5723 5725 Flow 

5736 5725? Flow 

5815 Basalt Flow 

5815A Basalt Flow 

5816 5713/5725 Flow 

5830 5725 Flow 

5831A 5733 Flow 

6701A Basalt Flow 

6711 Basalt Flow 

6807 6807 Vent 

8

2A06 3036B Flow 

3812 Flow 

4626 4626 Vent 

5734A 5734E Flow 

5734B 5734B Vent 

5734C 5734E Flow 

Map 

sheet 

E 

E 

c 

c 

c 

c 

c 

c 

c 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

E 

E 

c 

SP 

SP 

SP 

Location 

NavfNt 

(or Nt) 

Mean remanent magnetism 

Polarity 

BRUNHES ROCKS-Continued 

BASALTIC ROCKS-Continued 

Dated-Continued 

AFD 

(Oe) Field relations 

35.38 11152 29130 N 346 58 1 499 NRM Sunset basaltic 

stage. 

35.37 111.50 

35.28 111.86 

35.27 111.86 

35.27 111.76 

35.32 111.84 

35.35 111.80 

35.36 111.80 

35.49 111.68 

35.57 111.69 

35.57 111.70 

35.54 111.62 

35.51 111.60 

35.55 111.52 

35.55 111.53 

35.54 111.55 

35.51 111.57 

35.51 11158 

35.66 111.59 

35.65 111.61 

35.65 11158 

35.33 111.26 

35.40 111.43 

35.44 111.73 

35.51 111.63 

35.51 111.64 

35.51 111.63 

22/25 N 350 59 2 398 

Dated by field relations 

6/6 

5!6 

4/6 

6/6 

4/6 

5/6 

6/6 

6 

6!6 

6/6 

6!6 

5 

6 

6/6 

7/8 

9/9 

4/6 

8/8 

12/12 

8/13 

6/6 

8/8 

6/6 

6/6 

N 

N 

N 

N 

N 

N 

N 

N? 

N 

N 

N 

N? 

N? 

N 

N 

N 

N 

N? 

N 

N 

N 

N 

N 

N 

N 

21 43 14 23 

6 59 13 35 

2 37 35 8 

7 61 6 127 

290 74 18 26 

307 54 15 29 

21 27 4 238 

7 43 9 53 

14 53 18 14 

290 55 31 6 

347 57 10 44 

14 49 3 346 

14 50 6 70 

357 66 6 218 

359 45 24 34 

9 29 4 150 

5 56 4 163 

343 46 5 153 

50 33 10 33 

20 45 8 75 

19 52 6 115 

400 Sunset basaltic 

stage. 

500 Same as site 3534 --

750 Same as site 3534 --

250 Younger than basalt 2616. 

250 Older than 2620, 

3521; younger 

than benmoreite 

2530, 2533, basalt 2616. 

250 Older than basalt 

2616,3523, 

3621/3621A, 

3630. 

500 Same as site 3619 --

750 Younger than 

5718. 

Younger than basalt 7817. 

330 Same as site 4 705 --

170 Younger than rhyolite (unsampled, 

0.80±0.11 Ma).a 

500 Same as site 5723 --

Younger than rhyolite (unsampled, 

0.80±0.11 Ma).a 

Same as site 5815 --

270 Older than 5725 ----

330 Same as site 5723 --

330 Younger than 

5831. 

500 Younger than 

6713. 

Older than 5703; 

younger than 

basalt 7817. 

330 Younger than 

6713. 

200 Merriam basaltic 

stage. 

400 Merriam basaltic 

stage. 

250 Merriam basaltic 

stage; younger 

than Walker 

Lake sediment 

(unsampled, 

16.79±0.13 ka).6 

330 Merriam basaltic 

stage. 

250 Merriam basaltic 

stage. 

250 Same as site 

5734A. 

32 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

. K-Arage 

(Ma) 

4A.D.1180 

4A.D.1220 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

sne No. 

1436 

1520 

2621 

3517B 

3523A 

3601 

3605 

3606 

3607 

3607A 

3627 

3705 

3817 

3817A 

3818 

4603 

4606A 

4613 

4614 

4625 

4627A 

4629 

4632 

4635 

4704 

4704A 

4707 

4709 

4710 

4714 

4714A 

4715 

4715A 

4715B 

4715C 

4717 

4717A 

4719 

4720 

4726 

Rock type 

or vent No. 

1520 

1520 

2621 

3523 

3523A 

3601 

Basalt 

3606 

3607 

3512 

3627 

3705 

3817 

3808 

3818 

4603 

3606 

4613 

4614 

4625 

4635A 

4629 

4631 

4635 

4704 

5733 

4707 

4703 

4710 

4714 

4711 

4715 

4715A 

4715B 

4715C 

4717 

4708A 

4719 

4720 

4726 

Feature 

Flow 

Vent 

Vent 

Flow 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Map 

sheet 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

E 

E 

E 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

Location Mean remanent magnetism 

35.15 

35.19 

35.27 

35.37 

35.34 

35.40 

35.41 

35.40 

35.39 

35.39 

35.35 

35.41 

35.39 

35.39 

35.39 

35.49 

35.49 

35.47 

35.46 

35.44 

35.43 

35.44 

35.43 

35.42 

35.49 

35.49 

35.47 

35.48 

35.48 

35.46 

35.47 

35.47 

35.48 

35.46 

35.46 

35.47 

35.47 

35.44 

35.47 

35.44 

NaviNt 

(or Nt) Polarity 

BRUNHES ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated 

111.92 

111.89 

111.78 

111.88 

111.84 

111.71 

111.79 

111.81 

111.79 

111.81 

111.75 

111.67 

111.57 

111.57 

111.59 

111.74 

111.80 

111.70 

111.72 

111.71 

111.74 

111.77 

111.78 

111.72 

111.67 

111.65 

111.69 

111.65 

111.63 

111.63 

111.63 

111.64 

111.63 

111.64 

111.64 

111.68 

111.67 

111.69 

111.68 

111.62 

11/20 

7/8 

6/6 

6/6 

5!5 

5!6 

5!6 

4/6 

617 

517 

5/6 

5/6 

517 

517 

5!6 

4/6 

8/10 

6!6 

717 

5!6 

5!6 

4/6 

5!6 

6/6 

5!5 

4!6 

6/6 

6!6 

6!6 

5!5 

5!6 

5!6 

6/6 

6/6 

5/5 

5/8 

4/6 

5!6 

8/8 

6!6 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

3 

359 

21 

32 

336 

305 

13 

305 

299 

9 

311 

284 

330 

292 

30 

339 

321 

26 

300 

34 

336 

347 

0 

5 

351 

4 

51 

41 

339 

14 

344 

329 

335 

28 

7 

348 

2 

324 

356 

4 

45 

45 

47 

31 

46 

39 

49 

31 

27 

54 

45 

50 

45 

35 

48 

29 

33 

54 

47 

38 

75 

54 

51 

83 

42 

56 

43 

49 

37 

42 

46 

41 

37 

50 

50 

56 

40 

54 

52 

56 

19 

3 

21 

25 

31 

27 

28 

27 

19 

7 

38 

3 

8 

11 

18 

24 

10 

4 

16 

27 

4 

23 

8 

19 

24 

10 

7 

14 

10 

14 

20 

15 

14 

14 

19 

37 

20 

36 

14 

12 

AFD 

(Oe) 

7 NRM 

519 250 

11 250 

8 250 

7 500 

9 1000 

8 500 

12 750 

14 250 

133 250 

5 500 

741 250 

91 250 

52 250 

20 250 

15 250 

30 250 

319 250 

15 250 

9 250 

425 250 

17 750 

76 250 

13 1000 

11 500 

83 250 

95 250 

33 500 

63 250 

33 500 

16 250 

26 250 

24 250 

24 250 

18 500 

5 750 

22 250 

6 750 

17 250 

31 500 

Field relations 

Same as site 1520 --

Younger than 

1430, 1505/1506/ 

1508/2436. 

Older th.'Ul 3608, 

3619; younger 

than 3507, 3517, 

3518. 

Older th.'Ul 3521, 

3523. 

Older than rhyolite 

3612. 

Older than 3621/ 

3621A. 

Older th.'Ul 

4625?; younger 

than andesite 

4804? 

Younger than 4614 

Older th.'Ul 4613, 

5626. 

Older than 4715, 

4728; younger 

th.'ln 3705?, 

4726. 

Older than 4536----

Younger than 

4715A. 

Younger th.'ln andesite 4804. 

Younger th.'ln 

4625. 

Older than 4710----

Older th.'Ul 3705?, 

4625. 

K-Arage 

(Ma) 

Table 4 33 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Site No. 

4729 

4729A 

4819 

1

4912A 

5615 

5624 

5702 

5702A 

5711 

5714 

5717 

5728 

5808 

5833A 

6725 

6726A 

7806 

2818 

3520 

3523 

3528A 

3528B 

3610 

3622 

3630 

4402 

4402A 

4408 

4414 

4426 

Rock type 

or vent No. 

4729 

4728 

4819 

4836 

5626 

4603/4614 

5702 

5715 

5712 

5713 

5716 

5732 

5712? 

3705? 

6725 

6735 

Basalt 

2818 

Basalt 

3426 

3529 

3523 

3528A 

3528A 

3610 

3615 

3630 

4402 

4402 

4408 

4414 

4425 

Feature 

Vent 

Vent 

Vent 

Flow 

Flow 

Flow 

Vent 

Flow 

Vent 

Vent 

Flow 

Flow 

Flow 

Flow 

Flow 

Vent 

Flow 

Vent 

Flow 

Flow 

Vent 

Vent 

Vent 

Flow 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Vent 

Flow 

Location Mean remanent magnetism 

Map 

sheet Lat N. 

(0) 

c 

c 

c 

E 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

SP 

c 

E 

c 

35.44 

35.44 

35.45 

35.47 

35.58 

35.54 

35.58 

35.56 

35.56 

35.55 

35.55 

35.52 

35.56 

35.50 

35.61 

35.60 

35.55 

35.30 

35.25 

35.34 

Polarity Inc 

CO> 

BRUNHES ROCKS-Continued 

BASALTIC ROCKS-Continued 

Undated-Continued 

111.67 

111.66 

111.59 

111.38 

111.74 

111.70 

111.61 

111.62 

111.61 

111.61 

111.66 

111.65 

111.56 

111.56 

111.60 

111.61 

111.53 

111.58 

111.40 

111.95 

5/6 

5/6 

6/6 

5/6 

6/6 

6/6 

8/8 

6/6 

5/5 

8/8 

8/8 

4/6 

717 

6/6 

6/6 

6/6 

6/6 

N 

N 

N 

N 

N? 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

290 

8 

28 

345 

340 

30 

8 

15 

2 

10 

357 

1 

344 

353 

8 

29 

Brunhes or Matuyama 

5!6 

5/6 

6/6 

N 

N 

N 

11 

350 

349 

57 

61 

12 

55 

19 

53 

64 

58 

55 

48 

61 

55 

58 

42 

56 

47 

50 

35 

49 

c 3536 111.86 8/8 N? 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

c 

35.34 111.84 

35.36 

35.36 

35.39 

35.37 

35.34 

35.49 

35.49 

35.47 

35.46 

35.44 

111.86 

111.86 

111.74 

111.75 

111.80 

111.94 

111.94 

111.99 

111.93 

111.94 

6 

4/6 

5!6 

6/6 

4/6 

6/6 

8/8 

4/6 

7/8 

4/6 

4/6 

N? 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

354 

261 

308 

31 

350 

11 

351 

13 

23 

344 

37 

63 

31 

34 

30 

85 

76 

61 

58 

63 

22 

4 

20 

15 

18 

10 

10 

10 

7 

5 

4 

10 

10 

19 

6 

17 

9 

13 

12 

32 

29 

19 

9 

22 

6 

11 

3 

25 

7 

34 Magnetostratigraphy of the San Francisco Volcanic Field, Arizona 

13 

447 

12 

26 

15 

33 

50 

65 

60 

155 

472 

50 

47 

13 

152 

16 

73 

35 

34 

9 

8 

13 

103 

10 

91 

70 

323 

14 

172 

AFD 

(Oe) 

500 

250 

1000 

500 

330 

270 

170 

330 

330 

330 

330 

500 

170 

270 

270 

500 

500 

500 

250 

500 

500 

1000 

NRM 

250 

250 

250 

250 

250 

250 

Field relations 

Younger than 

4625. 

Older than andesite 

4804. 

Older than 3812----

Younger than 

4603/4614. 

Older than 5626 ----

Tappan basaltic 

stage. 

Tappan basaltic 

stage. 

Tappan basaltic 

stage. 

Tappan basaltic 

stage. 

Tappan basaltic 

stage. 

Tappan basaltic 

stage. 

Same as site 5711 --

Tappan basaltic 

stage. 

Older than 4536; 

younger than 

basalt n23. 

Older than dacite 

2713. 

Younger than benmoreite 3423A, 

3424. 

Younger than rhyolite 3425, 3518. 

Older than 3608, 

3619;younger 

than 3507, 3517, 

3518. 

Same as site 

3528A. 

Older than 3619, 

3621!3621A. 

Same as site 4402 --

Younger than 

4301. 

Younger than trachyte 4424. 

Younger than 

4301,4427A, 

4435A. 

K-Arage 

(Ma) 
Table 4. Paleomagnetic, stratigraphic, and chronologie data for sample sites in the San Francisco volcanic field, ArizonaContinued 

Location Mean remanent magnetism 

sne No. Rock type Feature Map AFD FJeld relations K-Ar age 

or vent No. sheet Lat N. LongW. NaviNt Polarity Dec Inc " (Oe) (Ma) 

(0) (0) (or Nt) (0) (0) «e (0) 

BRUNHES ROCKS-Continued 

BASALTIC ROCKS-Continued 

Brunhes or Matuyama-Continued 

4522C 4521 Flow c 35.45 111.85 6/6 N 347 53 7 99 250 Same as site 

4528A 

4526B 4535 Vent c 35.43 111.83 5/6 N 2 25 31 7 750 Younger than dacite 4526A, andesite 4536A. 

4528 4528 Vent c 35.44 111.87 5!6 N 351 61 5 239 250 ------------------------ 4528A 4521 Vent c 35.44 111.87 6/6 N 37 61 10 45 750 Older than 4536; 

younger than 

trachyte 4424, 

4527,4517. 

4606 4606 Vent c 35.50 111.81 6/6 N 354 74 3 600 250 Older than 4624, 

5535;younger 

than 4609, 5630. 

4619 Basalt Flow c 35.45 111.79 5/5 N 345 55 13 33 250 ------------------------ 4622 4622 Vent c 35.45 111.75 6/6 N 11 62 12 32 750 ------------------------ 4627 4627 Vent c 35.44 111.75 6/6 N 16 68 9 56 250 ------------------------ 1

4912 Basalt Flow E 35.47 111.38 5!6 N 357 30 30 8 500 ------------------------ 5505 5536 Flow NW 35.58 111.88 6 N? Same as site 

5536? 

5520 5529 Vent NW 35.53 111.87 7/8 N 357 59 7 68 250 Younger than 

5411,5413. 

5526A 5535 Vent NW 35.51 111.83 6/6 N 28 70 2 1662 250 Older than 4536; 

younger than 

4606/5536. 

5536 5536 Vent NW 35.51 111.81 6 N? Older than 4536; 

younger than 

5411. 

5536A 4606/5536 Flow NW 35.50 111.81 6 N? Older than 4624, 

5535;younger 

than 4609, 5630. 

5734 5734 Vent SP 35.51 111.64 5/6 N 307 62 22 13 500 ----------------------- 5810 Basalt Flow SP 35.55 111.56 7 N? Older than 5712?; 

younger than 

basalt 6835. 

5816A Basalt Flow SP 35.54 111.54 6/6 N 353 66 37 4 330 Older than basalt 

5815. 

5817 Basalt Flow SP 35.56 111.54 8/8 N 344 45 22 7 330 Same as site 5810--

7723A Basalt Flow SP 35.71 111.62 9/9 N 24 23 20 7 750 Older than 4624, 

basalt 7817; 

younger than 

basalt 7723. 

1

J.N. Kellogg (written common., 1976) 

8

C.W. Naesar and GA lzett (written common., 1987) 

3

Champion (1980, table 1) 4

Date from secular variation of geomagnetic pole position (D.E. Champion, written common., 1985) 6

S.W. Robinson (written common., 1983) 

Table 4 35 

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