( / 

Late CenozoiC Stratigraphy of the 

Feather and Yuba Rivers Area, California, 

with a Section on Soil Development in 

Mixed Alluvium at Honcut Creek 

/ rU.S. GEOLOGICAL SURVEY BULLETIN 1590-G 
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' ,,t ·, - I, .... 

Chapter G 

Late Cenozoic Stratigraphy of the 

Feather and Yuba Rivers Area, California, 

with a Section on Soil Development in 

Mixed Alluvium at Honcut Creek 

By ALAN j. BUSACCA, MICHAEL j. SINGER, and 

KENNETH L. VEROSUB 

U.S. GEOLOGICAL SURVEY BULLETIN 1590 

SOIL CHRONOSEQUENCES IN THE WESTERN UNITED STATES 

\ 
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 1989 

For sale by the Books and 

Open-File Reports Section, 

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Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Busacca, Alan j. 

Late Cenozoic stratigraphy of the Feather and Yuba Rivers area, California : 

with a section on soil development in mixed alluvium at Honcut Creek I by 

Alan j. Busacca, Michael j. Singer, and Kenneth L. Verosub. 

p. em. - (Soil chronosequences in the western United States; ) 

(U.S. Geological Survey bulletin ; 1590--G) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1590--G 

1. Geology, Stratigraphic-Cenozoic. 2. Geology-California-Feather 

River Region. 3. Geology-California-Yuba River Region. 4. Soil 

formation-California-Honcut Creek Region. I. Singer, Michael j. (Michael 

john), 1945- . II. Verosub, Kenneth L. Ill. Title. IV. Series. V. Series: 

U.S. Geological Survey bulletin; 1590--G. 

QE75.B9 no. 1590--G 557.3 s-dc20 89-600086 

[QE690] [551.7'8 1097943] CIP 
FOREWORD 

This series of reports, "Soil Chronosequences in the Western United States," 

attempts to integrate studies of different earth-science disciplines, including pedology, 

geomorphology, stratigraphy, and Quaternary geology in general. Each discipline 

provides information important to the others. From geomorphic relations we can 

determine the relative ages of deposits and soils; from stratigraphy we can place age 

constraints on the soils. Field investigations and mineralogic and sedimentologic studies 

provide information on the nature and types of deposits in which soils form. As a result 

of our work, we have estimated rates of soil formation, inferred processes of soil 

formation from trends in soil development with increasing age, and obtained information 

on the types of weathering that occur in various areas. In return, soil development and 

soil genesis have provided data on the age of landforms; the timing and duration of 

sedimentation, and, in some cases, the history of climatic fluctuations. 

Between 1978 and 1983, a coordinated and systematic study was conducted on soil 

development in different types of geologic deposits in the Western United States. The 

goals of this project, led by the late D.E. Marchand and subsequently by M.N. Machette, 

were to learn whether rates of chemical, physical, and mineralogic transformations could 

be determined from soil chronosequences; hqw these rates vary in different mineralogic 

and climatic environments; and how accurately soils can be used for such problems as 

estimating the ages of deposits, periods of landscape stability, and timing of fault 

movements. This series of reports presents data from several soil chronosequences of 

that project. 

More than 100 analyses on more than 1,000 samples were performed on soils 

collected in the Western United States. Some results have appeared in various books, 

journals, and maps (for example, Harden and Marchand, 1977, 1980; Burke and Birkeland, 

1979; Dethier and Bethel, 1981; Marchand and Allwardt, 1981; Meixner and Singer, 1981; 

Busacca, 1982; Harden, 1982a,b; Harden and Taylor, 1983; Machette, 1983; Machette and 

Steven, 1983; Busacca and others, 1984; Machette and others, 1984; Reheis, 1984). In the 

reports in this series, the basic field information, geologic back&round, and analytical 

data are presented for each chronosequence, as well as some results additional to the 

previous publications. 

One of the most significant aspects of these chronosequence studies is that in every 

study area, many soil parameters change systematically over time, or with the age of 

deposits. As Deming (1943) emphasized, it is this recurrence of correlation in such 

different conditions that is most significant to geologic and pedologic studies. In 

relatively moist areas, such as coastal and central California, such soil properties as 

percent clay or reddening of soil colors change most systematically over time. In more 

arid regions, such as in the Bighorn basin of Wyoming, calcium carbonate and gypsum 

contents best reflect relative ages of the deposits. A few parameters-for example, 

elemental composition of sands or clays-appear to be comparable between areas so 

diverse in climatic setting. 

Numeric age control has enabled us to estimate rates of soil development. In some 

places, we have been able to compare rates. between different areas. For example, in 

central California, rates of clay accumulation were found to be most rapid during the 

initial stages of soil development; the rates declined with increasing age. The straightest 

lines for regression were on a log-log scale. In coastal California, rates of clay 

accumulation appeared to be much higher than in central California. This difference in 

rates could be due to parent material (the coastal soils that we studied formed on 

reworked shale and sandstone, whereas central California soils were developed in granitic 

alluvium), and (or) the differences in rates could be due to eolian additions of clay. In 

the Bighorn basin of Wyoming, rates of clay accumulation, as well as most other soil 

properties, increased linearly over time, with no apparent decrease in initial rates. 

The data we present here suggest many opportunities for further interpretation. 

For example, we may learn how climate, vegetation, and mineralogy affect the rates of 

clay formation or organic-matter accumulation. In some study areas, we present data 

for rare-earth elements, which could be used to examine how each element reacts in 

different weathering environments. These examples are only a fraction of the possible 

future studies that could be conducted on the data presented here. 

J.W. Harden 

Editor 

Ill 

CONTENTS 

Foreword III 

Abstract G1 

Introduction G2 

Diagnostic stratigraphic criteria and methods G5 

Stratigraphic criteria G5 

Dating methods G5 

Paleomagnetic stratigraphy G5 

Radiocarbon dating G5 

Potassium-argon radiometric dating G5 

Tephrochronology G5 

Geologic mapping G6 

Geographic and geologic setting G6 

Geographic setting G6 

Geologic setting G7 

Stratigraphy G7 

Previous work G7 

Description of stratigraphic units G10 

Basin deposits G 14 

Holocence alluvium G14 

Soil landscapes G 15 

Geochronology and correlation G 15 

Modesto Formation G 16 

Upper member G 16 

Lower member G 16 

Soil landscapes G 18 

Geochronology and correlation G 19 

Riverbank Formation G 19 

Upper member G20 

Lower member G20 

Soil landscapes G21 

Geochronology and correlation G22 

Laguna Formation G23 

Upper member G25 

Lower member G27 

Nomlaki Tuff member G28 

Post-Laguna, pre-Riverbank erosion G29 

Soil landscapes G29 

Geochronology and correlation G30 

Dacite unit G33 

Geochronology and correlation G35 

Pre-dacite Cenozoic units G36 

Deformation and tectonism G37 

Summary and discussion of geologic history and tectonics 

Soil chronosequence site selection, excavation, and sampling 

Characteristics of the soil chronosequence G43 

Review of state factors G44 

Climate G44 

Organisms G45 

Parent material G45 

Soil development G48 

Soil development index G48 

G39 

G41 

Contents V 
VI Contents 

Mineralogy of the clay fraction G55 

Elemental composition of silt-size fractions G56 

Summary of trends in soil development and their use in soil correlation G62 

References cited G63 

Supplementary tables G68 

FIGURES 

1. Index map of study area G3 

2. Generalized geologic map of study area GS 

3. Schematic cross sections on and south of Honcut Creek G 15 

4. Schematic cross sections showing inferred extension of Prairie Creek and Magalia 

lineament fault zone G24 

5. Correlation of samples with an established magnetic polarity time 

scale G31 

6. Index map showing sample sites of chronosequence soil profiles G42 

7. Plots of estimated rainfall from Miocene to Quaternary time in west-central 

California and central Sierra Nevada G44 

8-16. Plots of: 

8. Percent clay-free sand versus depth in replicate soil profiles formed in 

Holocene_alluvium G46 

9. Horizon index versus depth of soil horizons in replicate soil profiles formed 

in alluvium of chronosequence members G51 

10. Composite depth showing soil development quantified by average values of 

horizon indices of replicate profiles calculated at 10-cm intervals for 

soils G53 

11. Age trend of soil development showing profile indices versus soil 

age G54 

12. Relative abundance of clay minerals determined by X-ray diffraction versus 

soil age G55 

13. Si02 in coarse-silt fraction of surface horizons versus soil age G58 

14. Ratio of Fe20 3 in percent to Zr in ppm x 100 in fine-silt fraction of surface 

horizons versus soil age G58 

15. Fraction of original content of elemental oxides remaining in fine-silt fraction 

versus soil depth G61 

16. Fraction of original content of elemental oxides remaining in fine-silt fraction 

of surface horizons versus soil age G62 

TABLES 

1. Stratigraphic correlations G4 

2. Comparison of areally and stratigraphically important soils in the project area with 

soil series designated in soil surveys Gll 

3. Age control for alluvial units in the Feather and Yuba Rivers area, and correlation 

of units to the northeastern San Joaquin Valley G12 

4. Comparison of stratigraphic interpretations of an exposure in the Thermalito 

Power Canal at Cherokee Bridge G36 

5. Site locations, assumed ages, and taxonomic subgroups of the soils sampled for 

the chronosequence study G43 

6. Comparison of the effect of stratification in a Holocene soil profile on texture versus elemental composition G47 

7. Comparison of the effect of textural stratification on elemental composition of 

coarse versus fine silt in a soil profile on the lower member of the Modesto 

Formation G48 

8. Average values of element concentration in coarse and fine silt fractions of BC 

and C horizons of the chronosequence soils G49 

9. Selected morphological and physical properties of the chronosequence 

soils GSO 
10. Comparison of profile indices for·soils from Honcut Creek and the Merced River 

that are approximate stratigraphic equivalents G52 

11. Relative enrichment and depletion of elements in the fine silt fraction of A horizons of the chronosequence soils G56 

12. Ratios of elements to zirconium in fine-silt fraction of selected horizons of soil 

formed on lower member of the Laguna Formation G57 

13. Concentration ratios for zircon in fine- and coarse-silt fraction of chronosequence 

soils G58 

14. Effect of stratification on the calculation of percentage of original content of elements remaining in the fine-silt fraction of a Holocene soil using Zr as a stable 

i.ndex G59 

15. Percentage of original content of elements remaining in the fine-silt fraction, calculated using Zr as a stable index G60 

16. Percentage of original content of elements remaining in the coarse-silt fraction, 

calculated using Zr as a stable index G60 

SUPPLEMENTARY TABLES 

1. Site locations and field descriptions G68 

2. Physical properties G80 

3. Extractive chemical analyses G84 

4. Clay mineralogy of the coarse and fine fractions G86 

5. Total chemical analyses of the fine f.raction by X-ray fluorescence G94 

6. Total chemical analyses of the 2-20 J.Lm fraction and the 20-50 J.Lm fraction by X-ray 

fluorescence for major oxides and trace elements G98 

7. Total chemical analyses of the fine fraction by instrumental neutron 

activation G114 

8. Calculated values of the Soil Development Index G126 

9. Radiocarbon ages and K-Ar radiometric ages of dacite blocks from lahar of the 

dacite unit G 128 

10. Tephra correlation G 130 

11. Paleomagnetic determinations G 131 

SUPPLEMENTARY FIGURE 

1. Stereographic projections of data from paleomagnetic studies G 132 

Contents VII 
Late Cenozoic Stratigraphy of the 

Feather and Yuba Rivers Area, California, 

with a Section on Soil Development in 

Mixed Alluvium at Honcut Creek 

By Alan j. Busacca, Michael j. Singer, and Kenneth L. Verosub 

Abstract project area. We associate a normal-to-reversed transition 

in magnetic polarity in the upper member of the Laguna 

We describe a sequence of upper Tertiary and Qua- with the boundary between the Gauss Normal- and 

ternary alluvial deposits for the area of the Feather and Matuyama Reversed-Polarity Chrons dated elsewhere at 

Yuba Rivers in the Sacramento Valley, California, and we 2.48 Ma. 

correlate these deposits with existing stratigraphic units to A lahar and volcanic sediments that contain dacitic 

the south in the northeastern San Joaquin Valley. We also clasts underlie the Laguna Formation and have only limdescribe our studies of relict and exhumed soils formed ited surface exposure. Previous workers interpreted this 

on six of these deposits at Honcut Creek in the center of volcanic unit to lie stratigraphically below the Miocene 

the project area. The soils were examined in order to Lovejoy Basalt (basalt of Table Mountain) and attributed a 

establish a soil chronosequence to evaluate the systematic Miocene age to it. Blocks of dacite from the lahar have a 

changes in soil profile properties with increasing age of mean whole-rock K-Ar age of 3.2 Ma. New stratigraphic 

the deposits, and to evaluate the use of soils as correlation and geomorphic data plus the radiometric dating suggest 

and dating tools for deposits of the upper Cenozoic. a late Pliocene age and further constrain the time of 

Methods employed in developing the local stratigra- inception of alluvial valley filling. 

phy and in correlating deposits to the San Joaquin Valley The volcanic unit and the Laguna Formation are moninduded: (1) stratigraphic superposition of deposits, sev- oclinally folded or faulted along the edge of the foothills. 

eral of which are separated by buried soils, (2) relative Deformation occurred between about 3.0 and 1.5 Ma and 

elevation and degree of dissection of original surfaces of is perhaps a southerly extension of the Chico monocline, 

deposits, (3) contrasting development of soils on relatively which terminates 20 km to the north of the Feather River. 

uneroded surfaces of the deposits, (4) tephra correlation, Aligned north-south drainages in the Riverbank Formation 

(5) magnetostratigraphy, and (6) radiometric dating. suggest more recent minor deformation. 

The alluvial deposits form a poorly expressed set of Distinctive soils are associated with relict surfaces of 

inset terraces along the edge of the valley t.hat open to the each formation and member. The most recognizable field 

south and west to form a fan flood plain in which succes- properties that develop systematically with increasing soil 

sive deposits are buried in normal stratigraphic superpo- age are soil color, soil depth, and argillic B horizons. Soils 

sition. Some of the deposits therefore can be observed in formed in Holocene alluvium have 10 YR brown color 

both relict-surface and buried positions. Buried soils mark hues and A horizons that are less than 0.5 m thick. In 

substantial periods of stability between episodes of aggra- contrast, soils formed on the lower member of the Laguna 

dation. We recognize seven principal alluvial units and we Formation have 10 R red color hues and strong argillic B 

correlate these with members and informal units of the horizons that extend more than 5 m deep. We analyzed 

Modesto, Riverbank, and Laguna Formations, plus Ho- the soils to determine their morphologic, physical, chemlocene alluvium. We did not recognize an alluvial deposit ical and mineralogic properties. Properties that develop 

equivalent to the middle Pleistocene Turlock Lake Forma- most systematically with soil age are total profile develoption. We suggest that a major hiatus in deposition oc- ment, as quantified from field properties by the Harden's 

curred between the upper Pliocene and lower Pleistocene soil development index, and depletion of major elements 

Laguna Formation and the middle Pleistocene Riverbank from silt-size fractions as determined by X-ray fluoresFormation. cence spectroscopy. Changes in clay mineralogy with soil 

Tephra correlation and magnetostratigraphy provide age also are distinctive but are qualitative data. Nonconnew information on the age of the Laguna Formation. stancy of other soil-forming factors, principally parent 

Glass from fluvially laid tephra at or near the base of the material composition and topographic position, intralower member is correlated with the Nomlaki Tuff Mem- duces important variation in the age trends that we obber of the Tehama and Tuscan Formations and provides an served and limits the certainty with which soils can be 

age of 3.4 Ma for inception of alluvial deposition in the used to correlate and date alluvial deposits. Nevertheless, 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G1 
systematic change in soil properties over the 1.6 million 

year estimated age span of the chronosequence provides 

insight into near-surface weathering processes and provides a means to use soils as a tool in geologic studies. 

INTRODUCTION 

The 1975 earthquake near Oroville, California, which 

had a Richter magnitude of 5. 7, awakened strong interest 

and controversy about the late Cenozoic seismic and geologic history of the eastern margin of the Sacramento Valley 

and adjacent foothills of the Sierra Nevada. This area had 

not previously been considered to be one of active faulting, 

and several large engineering structures, most notably the 

Oroville Dam and reservoir complex and the proposed 

Auburn Dam, are located on or very near conspicuous 

topographic lineament-fault zones. Seismic and geologic 

studies made in the Oroville area after the 1975 earthquake 

(California Department of Water Resources, 1979; 

Woodward-Clyde Consultants, 1977; Sherburne and 

Hauge, 1975) were hampered by a lack of information on 

the ages and stratigraphic sequence of the alluvial deposits 

along the margin of the Sacramento Valley. Several photolineaments and, possibly, active faults trend through the 

alluvium in the Oroville area, but the significance of this 

cannot be assessed without information on the ages and 

identity of the deposits. J'hick upper Cenozoic alluvial and 

basin deposits that fill the Sacramento and San Joaquin 

Valleys have been studied in detail in several locations 

(Janda, 1966; Marchand and Allwardt, 1981; Helley and 

others 1981; Harwood and others, 1981). Until this study, 

however, the deposits in the Oroville area had been the 

subject of only reconnaissance-level geologic mapping 

(Davis and Olmsted, 1952; Olmsted and Davis, 1961; 

California Department of Water Resources, 1979; R. Ford, 

unpub. data of California Department of Water Resources, 

1966). 

We undertook this project to develop a coherent stratigraphy for the upper Tertiary and Quaternary deposits of the 

Feather and Yuba Rivers near Oroville (fig. 1). In addition, 

we wanted to study in detail the relict soils formed on the 

surfaces of these deposits, using the increasing degree of 

soil development with age as a means to correlate and 

approximately date the deposits. Relict and buried soils 

have become an important tool for Quaternary studies in 

recent years (Birkeland, 1984; Morrison, 1978), especially 

because Quaternary surficial deposits often lack datable 

horizons, and because correlation based on traditional 

stratigraphic methods can be difficult. 

Using stratigraphic, pedologic, paleomagnetic, and 

radiometric evidence, we have subdivided the alluvial fill 

into a sequence of terrace, flood plain, and basin deposits 

which are derived from the Feather and Yuba Rivers and 

which span a period of 3 million years. We correlate these 

deposits with the type Modesto, Riverbank, and Laguna 

Formations found in the northeastern San Joaquin Valley 

(Marchand and Allwardt, 1981) and thereby extend the late 

G2 Soil Chronosequences in the Western United States 

Cenozoic stratigraphy of the San Joaquin Valley to the 

Feather and Yuba Rivers area. Within the description of 

stratigraphic units, we discuss the characteristic soil landscapes and the typical soil series found on relict and eroded 

parts of each unit. 

In this report we describe the Modesto, Riverbank, and 

Laguna Formations as they occur in the project area, and we 

describe re(erence stratigraphic sections for the Laguna and 

Riverbank Formations. The Nomlaki Tuff Member of the 

Laguna, Tehama and Tuscan Formations (Russell and 

VanderHoof, 1931; Everndon and others, 1964; Harwood 

and others, 1981; Helley and Harwood, 1985) is bedded at 

or near the base of the Laguna Formation in the project area. 

Tephra correlation, paleomagnetic stratigraphy, and new 

radiometric dates described here provide a better picture of 

the age and history of the Laguna Formation than we have 

had before. 

We present new radiometric and stratigraphic evidence 

to show that the part of the volcaniclastic Mehrten(?) 

Formation of Creely ( 1965) that lies south of Table Mountain (fig. 1) is actually an independent and much younger 

stratigraphic unit and is of late Pliocene, not Miocene age. 

This newly described unit consists of dacitic lahars and 

volcaniclastic sedimentary rocks. It underlies virtually the 

entire upper Cenozoic alluvial pile in the project area and 

for this reason is an important stratigraphic marker. From its 

age and stratigraphic position, we infer that the dacitic unit 

may have been an early part of the eruptive sequence that 

also produced the Nomlaki Tuff Member of the Laguna, 

Tehama, and Tuscan formations. Table 1 shows the relationship of stratigraphic units used in this report to those 

used previously in the Sacramento and San Joaquin Valleys. 

We use the outcrop distribution of the stratigraphic 

units, their ages, their surface and subsurface elevations, 

and the slopes on marker beds and contacts of the units to 

reconstruct the history of late Cenozoic deformation in the 

area. 

In the second major part of the report, we discuss our 

rationale for describing, sampling, and analyzing the sequence of soils formed on the alluvial deposits at Honcut 

Creek (fig. 1). The soils differ greatly in age or time of 

development but have formed under similar conditions of 

climate, vegetation, topography, and parent material; thus 

they constitute a soil chronosequence. We -describe the 

morphology of the soils and discuss the major trends in soil 

development with increasing age of the deposits. The 

discussion of soil development is intentionally short and is 

meant primarily to introduce the reader to the extensive data 

on the morphology, chemistry, elemental composition, and 

mineralogy of the soils that are included in the supplementary tables. 

Acknowledgments. -Our work was performed as a 

part of the U.S. Geological Survey Soil Correlation and 

Dating Project of the late Denis E. Marchand, which has 

as its major goals, first, to use soils as tools for correlation 

and dating of Quaternary surficial deposits in the Western 
I 

I 

.L.ea~.tern boundary of upper I ctinozoic basin deposits 

I 

I 

\ 

\ 

j 

Butte j 

Basin / 

•a· \. 1ggs 

\ 

J 

./ ,..--

' ) 

I 

l"' 

\ 

~ 

I 

99 

( BUTIE CO 

- -rsUrrER CO 

\ 

J 

/ 

L-. 

Sutter/_ 

Buttes"-. 

Palermo. 

Area of figure 6 

0 2 4 

Figure 1. Index map of study area. Lined pattern is pre-upper Cenozoic bedrock. 

6 8 KILOMETERS 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California GJ 
~ 

~ 

1.1'1 

& 

n 

:r 

a 

0 = 

II> 

II) 

.Q 

c 

II) 

= 

~ II> 

:r 

;. 

II) 

:E 

II) 

II> 

;' 

... 

= c: 

a· II) 

Q. 

II) 

~ II> 

Table 1. Stratigraphic correlations 

SAN JOAQUIN VALLEY SACRAMENTO VALLEY 

GEOLOGIC MOKELUMNE MERCED EAST MERCED SAN NE. SAN AGE1 FEATHER OROVILLE OROVILLE OROVILLE OROVILLE CHICO N.W. SAC. CO., 

PERIOD RIVER AREA RIVER ARJEA STANISLAUS RIVER AREA JOAQUIN JOAQUIN Ma AND YUBA AREA AREA AREA OUADRA~LE MONOCLINE SACRAAENTO NORTH OF 

AND AND NORTH RIVER FAN VALLEY RIVER AREA AND N.E. VALLEY AMERICAN 

EPOCH MERCED SAC. VALLEY RIVER 

Gale and Arldey Davis and Arldey Janda Marchand and This Halley and C.D.W.R.' C.D.M.G.' Cresiy Harwood and Steele Shlemon 

others (1954) Hall (1959) (1962) (1965, 1966) Allwardt report Harwood (1979) (1975) {1965) others (1981) (1979) (1967b, 1972) 

(1939) (1981) (1985) 

IV 

~ 0 f-- Alluvium 

Rood1Jiain Alluvium and Alluvium and i Ill .0000 (0) Alluvium (0) Alluvium and Alluvium and Alluvium and 8 Alluvium allwium sand dunes sand dunes Alluvium - .003 (M) and basin deposits basin deposits --------- basin deposits 

~ ~ II (M) basin deposits 

- Orland high 

l(l) .004-.000 (l) floodplain 

Younge Upper .009-.014 0) Upper Upper Upper Yolo E Upper 

& Mbr. .f Mbr. Ol .f Mbr. & Mbr. & Mbr. Terrace LL Mbr. 

J Young allwial Modesto Fm. Modesto Fm. J -

J r--- J r-- J r-- Alluvium Alluvium Alluvium J i--

fan Older lower lower Lower lower Arbuckle Lower 

Mbr. Mlr. .029-.042 (H) Mbr. Mbr. Mbr. Terrace Mbr. 

>- (H) 

a: .103-.130 {G) 

~ Upper Pelkins a: E unit (G) 

.f Upper .f Upper E Upper Terrace w & ~ Low terrace LL - .260 (N) Mbr. Mbr. LL 

Mbr. --------- Riverbank Riverbank Riverbank i Middle i i i i ::::::1 w Victor Fm. and older Fm. Fm. Fm. unit (N) r-- r-- ---- 0 z fans 

~ ~ - .34G-.450 (J) ~ lower ~ lower ~ lower ~ lower Mbr. Mbr. Mbr. u::; urit (J) 

it Ash ol MI. Yourger lP .450 (F) Mailu'(F) Corring Upper E Mbr. .f lrit Terrace u.. - ' Red Bluff 01, Sequence Mbr. Fn.,IP. High Turlock Lake Turlock lake ~ Frianl P. ~ ~ .60 (E) \ 

, Fm.• - i-- terraces Fm. Fm. i Coteorar i Corcoran --------- Red Bluff - Fm. t2 Older t2 Lower at, Mbr. unil Turlock'. 

lake '_ --------- Fm. 

1.08 (D) 8asall (0) 

Arroyo Seoo North Merced North Merced --?·-c= Redding & - LWermosl at, Red Bluff 

gravel gravel gravel gavelblld Fm.• Older high 

I gravel floodplain ~ lower 

I ---------- ~ Mbr. Upper Cenozoic --------- I ~ 

China 2.4 (B) & China Hat t.llr. gravels 

~ Red Bluff 

gravel "' Hal :!! Unnamed' Formation 

& i~ ! ----- laguna Tertiary r· w laguna lower Fm. Con~omerate 

>- z :!! .~uscan Tehama a: w Fm. Mbr. ~ ! Fm. $ - , Fm. 1- ~ c ~ = a: lower t ~nc 1-

w urit 3.4 (A) A) 

I 

' 

• Nomlalli 

Tuft ~ A) A) 

3.2 (P) 

"'NomlakiTull Unnamed Mbr. (A) Dadtic 

r--w Mehrten Mehrten lahars (P) 'Mehrten? Mehrten 

~ Fm. Fm. Formation' Fm. 

~~-

'letters refer to the sources of ages used: To find the source reference lor a date in the •Age• cdumn, locate the index letter at that stratigraphic level in one of the reference cdumns. Time scale of Palmer (1982). 

'Califorria Department d Watet Reswrces. 

'Calilorria Division d Mnes and Geology. 

'The •ash of Mt. Maidu" has been renamed the •Rockland ash bed." 

SAC. CO., S.E. SUTTER AND 

SOUTH OF SACRAAENTO YUBA 

AMERICAN VALLEY COUNTY 

RIVER 

Shlemon Olmsted Davis and 

(1967b, 1972) and Davis Olmsted 

(1961) (1952) 

Alluvium and Alluvial fan Young 

basin deposits and aJlwi~ 

river deposits deposits 

.f Upper 

Mbr. 0 

J-:: Mbr. 

Victor Intermediate 

Fm. aJJwial 

deposit:; 

.f Younge 

channe .... 

I -----

~ Older 

channe 

Upper 

Mbr. 

r---

E Lower u.. 

~ Mbr. 

r-- ArroyoSeoo 

gravel 

~ 

Old 

alllNi~ 

deposits 

Arroyo Seoo 

gravel 

laguna laguna Formation Formation 

---------

l-M trans. 

-------·-

Mehrten 

Fm. 

'Red Bluff Formation of Halley and HaJWood (1985) in the Oroville area correlates physically with the u~t gravel bed d tlis report; the Turlock lake Formation of Halley and Harwood (1985) in the Oroville area correlates physically with pan ci the La~na Formation of this report. 
United States, and second, to establish a data base for soils 

from the chronosequences studied. We are indebted to 

Denis Marchand for the help that he gave so freely and to 

the U.S. Geological Survey for its financial support of this 

project. 

DIAGNOSTIC STRATIGRAPHIC CRITERIA 

AND METHODS 

Stratigraphic Criteria 

The delineation of a local stratigraphic sequence for the 

alluvial deposits of the Feather-Yuba Rivers area presents 

problems that are similar to those encountered elsewhere in 

the Great Valley. Units of widely varying age are often 

lithologically similar. The source areas and thus the characteristics of the gravel, sand, silt, and clay derived from a 

single drainage basin have not changed markedly over the 

time of deposition of the alluvium. Conversely, within a 

single mappable stratigraphic unit, nonsystematic lateral 

lithologic variation is commonly as great as the variation 

between units. Classical stratigraphic concepts are difficult 

to apply. Younger stratigraphic units in the project area 

locally lie in normal superposition over older units, but 

more often the younger units are inset into the older units, 

and therefore are topographically lower. 

In this study, five principal characteristics were used to 

differentiate stratigraphic units: ( 1) disconformities that 

could be recognized and traced laterally, such as truncation 

or incision of one alluvial fill by another or the presence of 

buried soils on former surfaces of older units; (2) distinctive 

lithology and stratigraphic superposition (for example, 

dacitic lahars overlain by cobbly, mixed-source alluvium); 

(3) relative elevation or position of geomorphic surfaces; (4) 

surface form and the degree of erosional dissection of 

original surfaces; and (5) contrasting degrees of development of surface soils on little-eroded remnant surfaces of 

different topographic elevations. Using these characteristics, and the relative and absolute dating methods discussed 

below, we define a local stratigraphic sequence that we 

correlate with the late Cenozoic stratigraphy of the northern 

Sacramento Valley (Helley and Harwood, 1985) and the 

northeastern San Joaquin Valley (Marchand and Allwardt, 

1981). 

Dating Methods 

Two methods of absolute radiometric dating and two 

methods of relative dating provided a limited chronologie 

framework in which to place the stratigraphic units. The 

four methods used were paleomagnetic stratigraphy, tephrochronology, K-Ar radiometric dating, and radiocarbon 

dating. Analytical results and the location of sampling sites 

are given in the supplementary tables. The interpretation of 

the results is discussed in the section titled ''Stratigraphy.'' 

Paleomagnetic Stratigraphy 

Approximately 50 oriented sediment samples were 

collected by standard methods for paleomagnetic polarity 

determination. Several sandy samples were lost because of 

disaggregation. All magnetic studies were performed in the 

paleomagnetics laboratory of the Geology Department of 

the University of California, Davis. Paleomagnetic measurements were performed on a Schonsted SSM-1 spinner 

magnetometer operating in a six-spin mode. Alternating 

field demagnetization of the samples was done with a 

Schonsted GSD-1 demagnetizer. 

Behavior of the samples during demagnetization is 

discussed and stereographic projections of paleomagnetic 

data for the samples are given in supplementary table 11. 

Radiocarbon Dating 

Eight samples of wood or charcoal were collected from 

streambank exposures for radiocarbon e4

C) dating. Individual samples consisted of one or more of the following: 

pieces of charcoal in individual sand lenses, remnants of 

bark, or conifer cone scales. One subsample was cut from a 

charred, transported tree stump. Samples were wrapped in 

aluminum foil at the site. Conventional 14C analyses were 

made on whole, hand-concentrated samples by Beta Analytic Incorporated, Coral Gables, Florida. 

Potassium-Argon Radiometric Dating 

Three large blocks of fresh, biotite-bearing .dacite from 

the lahar bed of the dacite unit were collected at two 

locations east and southeast of the town of Oroville. 

Potassium-argon ages were determined on both whole rock 

samples and biotite and hornblende separates of the dacites 

by Wendy Hillhouse of the U.S. Geological Survey. 

Tephrochronology 

Several samples of the "unnamed rhyolitic pumice 

tuff'' of Creely ( 1965) from the Oroville area and of a 

rhyolitic tuff from near the Yuba River were collected by 

U.S. Geological Survey geologists between 1975 and 1978. 

We collected samples of tuffaceous and pumiceous sediments from the project area, and the California Department 

of Water Resources gave us two additional samples collected from test wells in the Thermalito area west of 

Oroville. Andrei Sarna-Wojcicki of the U.S. Geological 

Survey analyzed glass from these tephra samples by 

geochemical methods for the purpose of correlating them 

with recognized, dated tephras at other locations. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California GS 
Geologic Mapping 

Geology was mapped at 7.5-minute scale (1:24,000) 

and compiled at 15-minute scale (1:62,500) (Busacca, 

1982). Soil surveys for the Oroville area (Carpenter and 

others, 1926), Yuba County (Herbert and Begg, 1969), and 

Sutter County (Lytle, in press) were particularly useful in 

the detailed mapping of stratigraphic units because of the 

general correspondence of soil associations to individual 

stratigraphic units. Black and white vertical aerial photographs of Yuba and Butte Counties, at 1:20,000 scale and 

dated 1962, were used for landform mapping; however, 

they predated only part of the large-scale land leveling of 

the low and intermediate terraces (Modesto and Riverbank 

Formations). Land leveling posed the most serious difficulty in subdividing and mapping members of the Modesto 

and Riverbank Formations. Both Landsat images and U-2 

high altitude vertical color photographs were used to map 

photo lineaments and other broad landform features. 

The Project Geology Branch of the California Department of Water Resources made available a wide range of 

· drillers' records and stratigraphic descriptions of test wells 

and excavation sites from engineering and geologic studies 

of the Thermalito Forebay and Afterbay complexes of the 

Oroville Dam Project. Subsurface correlations and part of 

the stratigraphic reconstruction discussed below arose from 

use of these materials and from access that the department 

provided to excavation sites. 

GEOGRAPHIC AND GEOLOGIC SETTING 

Geographic Setting 

The study area extends from Table Mountain north of 

the Feather River, southeastward along the terrace sequence 

at the eastern edge of the Sacramento Valley, to a point 

about 7 km south of the Yuba River (fig. 1). The western 

boundary of the area is the eastern border of the Butte basin. 

The project area included all of the Honcut, Palermo, 

Gridley and Biggs 7 .5-minute quadrangle maps and parts of 

the Shippee, Oroville, Bangor, Lorna Rica, and Browns 

Valley 7 .5-minute quadrangle maps. Elevations in the 

project area range from 18 m on the Feather River at the 

south edge of the area to 293 m on the highest point of 

upper-Tertiary gravel near the town of Bangor. 

The project area is underlain principally by unconsolidated alluvial deposits that form fan-shaped flood plains and 

uplifted, dissected terraces. These deposits are grouped 

with the valley-fill sediments of Cenozoic age that occur in 

other parts of the Sacramento Valley, and together form the 

Sacramento Valley geologic province (Olmsted and 

Davis, 1961). Remnants of several distinct high terraces are 

visible to the southeast from the flood plain of Honcut 

Creek. To the north near Oroville, the alluvial landscape 

has a stepped appearance that suggests multiple terrace 

G6 Soil Chronosequences in the Western United States 

levels. The deposits in the Feather and Yuba Rivers area 

record a complex cycle of alluvial fan and flood plain 

deposition followed by incision and erosional modification 

that has been repeated throughout late Tertiary and Quaternary time. Adding to the complexity, the deposits have been 

tectonically deformed. 

The drainage basins of the Feather and Yuba Rivers and 

of Honcut Creek lie with~n the Sierra Nevada geologic 

province. From the Sierran crest to the foothills, the Feather 

and Yuba basins drain primarily a sequence of weakly 

metamorphosed marine shale, phyllite, schist, slate, and 

quartzite of probable Mesozoic age (California Department 

of Water Resources, 1979); granodiorite, tonalite, and 

granite of Mesozoic age; and metamorphosed volcanic 

rocks, primarily andesite and basalt, which are interpreted 

as a Mesozoic ophiolite, that is, a remnant of subducted 

oceanic crust and sea floor (Schweickert and Cowan, 1975). 

Approximately 65 percent of the drainage basin of Honcut 

Creek is underlain by basic metavolcanic rocks, and the 

remainder is tonalite or granodiorite. The Feather and Yuba 

basins also drain remnants of Pliocene andesitic rocks, and 

all three basins contain remnants of early and middle 

Cenozoic auriferous gravels. The Cenozoic volcanic rocks 

and gravels cap ridges on the long western slope of the 

Sierra. 

The Feather River has a drainage basin area -of 9,350 

km2 above the town of Oroville (Davis and Olmsted, 1952). 

Within the Sacramento Valley, the Feather River maintains 

a southerly course for 78 km from Oroville south to its 

confluence with the Sacramento River at Verona. The 

southerly course allows the Feather River to act as a trunk 

stream along the eastern margin of the Sacramento Valley. 

To the east of the river lies the sequence of elevated, 

dissected alluvial terraces which are the subject of this 

study; to the west lie the recent basin deposits of the Butte, 

Sutter, and Yuba basins. 

Honcut Creek, with a drainage basin area above the 

town of Honcut of approximately 290 km2 , drains the 

foothill area between the Feather and Yuba basins. The 

Yuba River, with a drainage basin area_ of 3,092 km2 (Davis 

and Olmsted, 1952), flows west-southwest for 24 km from 

the mountain front to its confluence with the Feather River 

at Marysville. 

The present climate in the project area is a Mediterranean type. Summers are hot and dry, and winters are cool 

and wet. Mean annual temperature (MAT) at Marysville is 

16.7 °C (108 years of record); mean January temperature is 

7.5 °C and mean July temperature is 26 °C; more than 80 

percent of the mean annual precipitation (MAP) of 550 mm 

occurs between November and March (National Oceanographic and Atmospheric Administration, 1979). 

The MAT at Honcut Creek is nearly identical to that 

reported at Marysville. The MAP at Honcut Creek increases 

from 570 mm at its confluence with the Feather River to 680 

mm 13 km to the east at the valley edge (California 

Department of Water Resources, 1963). 
There is a strong orographic effect on cyclonic storms 

that approach from the Pacific Ocean to the west and rise to 

pass over the Sierran crest. MAP increases systematically to 

1 ,050 mm in the upper reaches of the Honcut Creek 

drainage, and to more than 2,000 mm in the upper Yuba 

River drainage; the maximum MAP in the Feather River 

drainage is more than 2,350 mm at Bald Eagle Mountain 

near Bucks Lake (National Oceanographic and Atmospheric 

Administration, 1979). 

Geologic Setting 

The alluvial deposits of the Feather River, and to a 

lesser extent those of the Yuba River and Honcut Creek, 

occur as a sequence of nested terraces that open into fans to 

the southwest and west toward the axis of the Sacramento 

Valley (fig. 2). Tectonic uplift and westward tilting of the 

Sierra Nevada has continued from the early Miocene to the 

present (Huber, 1981). As a consequence, the original 

depositional gradients of Tertiary and Quaternary volcanic 

and alluvial units in~rease with increasing age. For example, the present-day gradient on the Feather River below 

Oroville is 0.5-1.8 meters per kilometer, whereas the slope 

on the Miocene Lovejoy Basalt at Table Mountain is 22-33 

m/km. A similar pattern was documented in the Merced 

River area by Marchand (1977) and Arkley (1962). 

The uplift and westward tilting of the Sierra Nevada 

have combined with cyclical or episodic deposition of 

sediments to produce a distinctive pattern of alluvial landforms. Near the mountain front, successively older deposits 

stand at higher elevation than younger deposits, are more 

dissected, and bear soils of stronger profile development. 

Younger deposits are inset into older deposits to form a 

series of nested terraces. The surfaces of the deposits 

gradually converge to the southwest and west because older 

deposits have a steeper gradient than the younger ones; a 

few kilometers west of the mountain front the alluvial 

deposits occur in normal stratigraphic superposition with 

younger units progressively burying older. Buried soils 

mark the tops of some of the units in the subsurface. Several 

of the units thus have both surface and subsurface expression. Tectonic deformation of the alluvium along the 

mountain front during the Pliocene and Pleistocene has 

increased the complexity of this pattern, and gold dredging 

and agricultural land leveling serve to further obscure the 

geomorphic sequence. 

Marchand ( 1977) postulated that the regular cycles of 

alluvial fan building, river incision, and soil formation in 

the northeastern San Joaquin Valley were keyed to Pleistocene glacial-interglacial climatic change in the Sierra 

Nevada. He cited several lines of evidence from his own 

previous work as well as that of Arkley (1962), Janda 

(1965, 1966), and Janda and Croft (1967) to support 

this view. In brief, he envisioned the deposition of fine 

granitic rock flour during glacial advance as the initial stage 

in a cycle of fan-flood plain deposition. This was followed 

by deposition of unweathered cobbly alluvium during glacial retreat, as formerly glacier-filled valleys were flushed 

of coarse sediment. Finally, river incision occurred during 

interglacial periods or early in the next glacial cycle when 

streamflow was high but sediment load was low. This 

hypothesis is consistent w.ith the observation that coarse 

sediments overlie fine in many of the alluvial units of the 

eastern San Joaquin Valley. Alluvial cycles in the Feather 

River and Yuba River basins may also have been controlled 

by glacial-interglacial climatic change, although the lower 

elevations in the northern Sierra compared to the central and 

southern Sierra may have modified the degree or timing of 

the response of the alluvi~l system to climate change. 

Alluvial deposits younger than the Pliocene dacitic 

volcaniclastic rocks in the project area primarily have a 

mixed mineralogy. This is a reflection of the several rock 

types in each drainage basin. In general, however, dark 

metavolcanic rocks and blue and white siliceous metasedimentary rocks are dominant in the gravelly alluvium. Clasts 

of various Mesozoic granitic and Tertiary volcanic rocks are 

less abundant.· Specific variations in lithology are due to 

local differences in source area, to reworking of alluvium, 

and to differential weathering of gravels within the deposits. 

Young alluvium along intermittent streams that drain from 

old deposits is commonly more weathered and redder than 

is alluvium of the same age along main rivers that drain 

from relatively unweathered bedrock. 

STRATIGRAPHY 

Previous Work 

Alluvial fan and dissected terrace deposits of late 

Cenozoic age in the Sacramento Valley were mentioned in 

some of the earliest geologic studies of this region. For 

example, Lindgren (1911) described a system. of three 

so-called gravel benches near Oroville along the Feather 

River, although he stressed that the threefold division of 

gravels was difficult to trace southward to the Yuba and 

Bear Rivers. Bryan (1923) recognized two broad terrace 

levels throughout the Sacramento Valley and hypothesized 

a tectonic or climatic origin. Russell (1931) identified but 

did not study in detail four terrace levels on the west side of 

the Sacramento Valley that are younger than the Pliocene 

Tehama Formation. 

In the early geologic studies, more attention was given 

to the prominent Pliocene alluvial and volcaniclastic deposits than to those of Pleistocene age. Russell (in Russell and 

VanderHoof, 1931) gave the name Tehama Formation to a 

thick sequence of fluvial sediments on the west side of the 

Sacramento Valley. Anderson and Russell (1939) described 

the Red Bluff Formation as a coarse, brick-red, gravelly 

alluvial deposit of variable thickness that unconformably 

overlies the Tehama. In subsequent years, the name Red 

Bluff has been used extensively in the Sacramento Valley, 

both formally and informally, to describe red gravelly 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G7 
~ 

00 

fJl 

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121 °45' 

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T 18 N 

T 18 N 

T 17 N 

R3E R4E 

e f\ichv<l!(! 

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EXPLANATION 

~ Alluvium (Holocene) 

~ Basin deposits (Holocene and Pleistocene) 

~ Modesto Formation (late Pleistocene) 

I Omu j Upper member 

~ Lower member-Locally Includes distributary 

deposits (d) 

~ Riverbank Formation (middle Pleistocene) 

~ Upper member 

~ Lower member 

!orlu I 

~ 

~ 

Laguna Formation (Pleistocene and Pliocene) 

Upper member (Pleistocene and Pllocene}-

Locally Includes uppermost gravel bed (g) of 

Pleistocene and Pliocene age. Remainder of 

member Is late Pliocene In age 

Lower member (Piiocene}-Locally Includes exhumed surfaces (TIIexl 

Nomlakl Tuff member (Pliocene) 

Figure 2. Generalized geologic map of study area. 

~ Dacitlc lahars and related sediments (Pliocene) 

~ Bedrock (pre-Pliocene) 

--?-- ·- Contact-Dashed where approximately located; 

· dotted where concealed; queried where 

uncertain 

----- Fault zone or lineament-Dashed where approximately located; CH, Cleveland Hills; SR • 

Swain Ravine; PC, Prairie Creek; M, 

Magalia 

-+ __ Anticline-Showing crestline; dashed where approximately located 

-+ __ Syncline-Showing trough line; dashed where 

approximately located 

A --- A' Line of section-See figure 4 

Site discussed In text 

~ Dredge tailings 

mo Hydraulic mining outwash 
alluvium derived from diverse sources and of probable 

different ages. For example, Creely (1965) extended the 

Red Bluff Formation into the Oroville area, using the name 

for all older uplifted terrace deposits. More recently, Helley 

and Harwood (1985), Harwood and others (1981), and 

Helley and others ( 1981) used radiometric and stratigraphic 

evidence to correlate the older, coalescing gravelly fan 

remnants on the east side of the Sacramento Valley with the 

Red Bluff Formation on the west side. 

Anderson (1933) described the Tuscan Formation as a 

series of volcanic mudflow breccias and volcanic conglomerates that blanket the west slope of the northern Sierra and 

extend into the Sacramento Valley. The Tuscan and the 

Tehama are both Pliocene in age, and the two formations 

interfinger in the subsurface of the Sacramento Valley 

(Anderson and Russell, 1939). The Nomlaki Tuff Member 

is interstratified at or near the base of both formations. 

Evernden and others (1964) dated a sample of the welded 

dacite tuff from Bear Creek Falls, which Anderson and 

Russell (1939) correlated with the type Nomlaki Tuff 

Member on the west side of the Valley, and reported a K-Ar 

age of 3.3±0.4 Ma. 1 

Pliocene and Pleistocene alluvial deposits have been 

studied in the greatest detail in the· northeastern San Joaquin 

Valley in conjunction with investigations of ground-water 

resources, and more recently, tectonic stability. Gale and 

others ( 1939) recognized and named three extensive deposits in the Mokelumne area: the Victor Formation (now 

obsolete), the Arroyo Seco Gravel, and the Laguna Formation. Arkley (1962) and Davis and Hall (1959) subdivided 

the Victor Formation into the Modesto, Riverbank, and 

Turlock Lake Formations. More recently, Shlemon (1967a, 

b; 1972) subdivided the upper Cenozoic alluvial deposits of 

the American and Mokelumne Rivers near Sacramento. 

Shlemon used a combination of existing and new formation 

names. Extensive mapping and detailed investigation of late 

Cenozoic alluvial deposits in the eastern San Joaquin Valley 

is summarized in Marchand ( 1977) and Marchand and 

Allwardt (1981). Marchand and Allwardt (1981) presented 

a comprehensive revision and updating of stratigraphic units 

in the northeastern San Joaquin Valley. From youngest to 

oldest, they recognized four distinct deposits of Recent age, 

two members of the Modesto Formation and three members 

of the Riverbank, two members of the Turlock Lake 

Formation, the North Merced Gravel, and two members of 

the Laguna Formation, including the China Hat Gravel 

member as the uppermost gravel unit of the Laguna. Helley 

(1979), Harwood and others (1981) and Helley and Harwood ( 1985) extended the formations and stratigraphy of 

Marchand and Allwardt (1981), with some modification, 

into the Sacramento area and throughout much of the 

Sacramento Valley. Shlemon and Begg (1972) delineated, 

but did not correlate, five sets of channel systems of 

1 Recalculated to 3.4±0.4 Ma, using the revised decay constants of 

Steiger and Jaeger (1977). 

G1 0 Soil Chronosequences in the Western United States 

different ages, all younger than the Red Bluff Formation, on 

Stony Creek in the western Sacramento Valley. Steele 

( 1979) recognized at least six strath terraces and fill 

terraces, all younger than the Red Bluff Formation, on the 

west side of the northern Sacramento Valley. 

In the Feather-Yuba Rivers area, Olmsted and Davis 

(1961) provisionally assigned the names alluvial deposits, 

Victor Formation, and Laguna Formation (following Gale 

and others, 1939) to young, intermediate, and old alluvial 

fan and terrace deposits, respectively. Their Laguna Formation corresponds approximately to deposits in the vicinity of Oroville assigned by Creely ( 1965) to the Red Bluff 

Formation. The different stratigraphic concepts and formation names that were developed independently in the Sacramento and the San Joaquin Valleys unfortunately overlap 

and conflict in the Feather-Yuba area. Recent mapping by 

the California Department of Water Resources ( 1979) and 

by the Division of Mines and Geology (Sherburne and 

Hauge, 1975), following the Oroville earthquake, was 

concentrated in the foothill areas where ground rupture 

occurred, and no attempt was made to revise or update the 

alluvial stratigraphy. 

Description of Stratigraphic Units 

In this section we describe the stratigraphic units and 

the common soil landscapes on relict and eroded areas of 

each unit. We list in table 2 the correspondence between 

soils that are areally and stratigraphically important and 

official soil series designated in soil surveys of the local 

area. The taxonomic classification of these soils is also 

given in table 2. The soils that we selected for the 

chronosequence study met a very specific set of conditions 

in order to best express the age or time of soil development 

on each unit; therefore, we describe and discuss the characteristics of these chronosequence soils in a separate 

section later in this report. 

We present current information on the ages of the units 

(table 3) and we correlate several of the informal members 

with informal members of formations used by Marchand 

and Allwardt (1981) in the northeastern San Joaquin Valley 

(table 1). Holocene basin deposits and alluvium, two 

members of the Modesto Formation and two members of 

the Riverbank Formation are described. Two informal 

members and one formal member of the Laguna Formation 

are recognized and supplemental reference sections are 

described. These we correlate, respectively, with the postModesto deposits, upper and lower members of the 

Modesto Formation, upper and middle units of the Riverbank Formation, and upper and lower units of the Laguna 

Formation of Marchand and Allwardt (1981). Dacitic lahars 

and volcaniclastic rocks that underlie the alluvial sequence 

are described and reference sections are presented for them. 

We did not recognize an equivalent deposit to the Turlock 

Lake Formation of Marchand and Allwardt (1981). We 

describe the stratigraphic units in age order from young to 
Table 2. Comparison of areally and stratigraphically important soils in the project area with soil series designated in soil 

surveys 

This report 

Informally designated 

Geologic unit soil series1 

Holocene and 

modem alluvium 

Modesto 

Formation 

Riverbank 

Formation 

Laguna Formation 

HoncuJ 

(Typic Xerorthents) 

Wyman variant 

(Typic Haploxerolls) 

Ryer series 

(Mollie Haploxeralfs)3 

Ryer duripan variant 

(Abruptic Durixeralfs) 

Ryer coarse variant 

(Typic Haploxerolls) 

Wyman series 

(Mollie Haploxeralfs)3 

Kimball series 

(Mollie Palexeralfs) 

Y okohl series 

(Abruptic Durixeralfs) 

Kimball deep variant 

(Mollie Palexeralfs) 

Redding series 

(Abruptic Durixeralfs) 

Red Bluff strong variant 

(Palexerults) 

Soil survey of the 

Oroville area, 

Califomia (Carpenter 

and others, 1926) 

Honcut loam 

Honcut loam, compact 

substratum phase 

Gridley clay loam 

Gridley clay 

Honcut sand 

Wyman loam 

Rocklin fme sandy 

loam 

Kimball loam 

Redding gravelly 

sandy loam 

_2 

1

Soils in italics sampled for the chronosequence study. 2

No equivalent soil series mapped in this area 30fficial series classification for Ryer and Wyman is Typic Haploxeralfs. 4

No equivalent landform or geologic formation. 

Soils of the Yuba 

area, Califomia 

(Herbert and Begg, 

1969) 

Honcut series 

(Typic Xerorthents) 

Wyman series 

(Mollie Haploxeralfs) 

Ryer series 

(Mollie Haploxeralfs )

3 

LOam and clay 

loam deep over 

substratum 

Loam and clay 

loam, moderately 

deep over 

substratum 

_2 

_2 

Wyman series 

(Mollie Haploxeralfs)3 

Kimball series 

(Mollie Palexeralfs) 

Y okohl series 

(Abruptic Durixeralfs) 

Ramona series on 

Yuba River only 

(Typic Haploxeralfs) 

Redding series 

(Abruptic Durixeralfs) 

_2,4 

Soil survey of Sutter 

County, Califomia 

(Lytle, in press) 

_2 

_2 

Marcum series, 40--60 in. 

(Typic Argixerolls) 

Gridley series, 20-40 in. 

(Typic Argixerolls) 

Yuvas series 

(Abruptic Durixeralfs) 

Liveoak series 

(Typic Haploxerolls) 

Conejo series 

(Pachic Haploxerolls) 

_4 

_4 

_4 

_4 

_4 

old rather than the conventional old to young because this 

order is more compatible with our studies of the soils 

formed on these units. A generalized geologic map is 

presented in figure 2. A detailed geologic map of the 

project area at 1:62,500 scale can be found in Busacca 

(1982). This geologic mapping, modified somewhat for the 

purposes of map compilation throughout the Sacramento 

Valley, also can be found in Helley and Harwood (1985). 

Table 3 presents the age control for the stratigraphic units to 

be described below. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G11 
~ Table 3. Age control for alluvial units in the Feather and Yuba Rivers area, and correlation of units to the northeastern San joaquin Valley 

~ 

Radiometric ages from the Central Valley (ka) 

til 

~ Geologic unit Stratigraphically Within unit Stratigraphically Inferred correlation Remarks Chrono- Age of surfaces Uncertainty 

n 

~ above unit below unit to NE San joaquin sequence assumed for of age 

c (limiting (limiting Valley (Marchand soils, this chronosequence estimates (ka), 

= 0 minimum) maximum) and Allwardt, 1961) study (ka) comments 

"' ~ 

..Q 

c 

~ Holocene alluviwn n = On Honcut Creek 0 1

0.450±0.45 1 ~ 3.020±0.160 Post-Modesto ill Well-vegetated natural HON-1 3Q.6 0-3.0 ka, range 

"' 1.775±0.110 levee and back-levee HON-2 in 14C ages from :r 

- deposits. These deposits HON-3 comparable sites ~ 

~ are incised into major suggest true age range ~ ~ flood plain surface on from 0.45 to 1.8 ka. ~ Feather River, and grade ~ 

= to similar deposits on c: Feather River. :!. 

;-

Q. 

l:a Major high 1

1.775±0.110 13.020±0.160 48.230±0.80 Post-Modesto II not 

a flood plain on sampled ~ 

"' Feather River 

Basin deposits 0 N.A.~ N.A.5 No correlative Stratigraphic position of not 

unit of base of unit is not sampled 

known 

Modesto Formation 

Upper member 13.020±0.160 N.A.5 4

•

6

31.24±0.32 Modesto Formation HON-5 10.0 3.0-29.0 48.230±0.80 714.1±0.203 29.41±2.03 upper member HON~ 

Lower member 14.1±0.20 N.A.5 8103±6 Modesto Formation HON-9 40.0 14.0-100.0, soil 7

29.41±2.03 lower member HON-10 development suggests 7

42.4±1.0 HON-11 that true age is 40,000 4

42.0±16.0 but range of estimate is 4

43.0±34.0 large because deposition 

not radiometrically dated 

in project area. 

Riverbank Formation 

Upper member 5

N.A. 9

<730 Riverbank Ages of 103 and 120 ka HON-13 130 50-250 ka, soil 8103±6 Formation are from upper unit in HON-14 development suggests 4 120±40 upper unit Sacramento area, and that true age of the 4 140±40 geomorphic surface of surface is approximately 4 145±20 that deposit can be traced 100 ka but range of 

to Oroville area. estimate is lage because 

deposit is not radiometrically dated in project. 
rCol 

;-

~ 

~ 

:::l 

0 

N 

0 

r;· 

~ e:. 

~· 

;:.1 

"C 

=r 

-< 

s. 

:;t 

~ 

.., 

~ 

Col 

:;t 

~ 

Col 

:::l 

Q. 

-< c 

aCol 

::-::1 <' 

~ 

~ ~ 

~ 

~ 

~ 

g: 

3 

iii' 

~ ... 

w 

Radiometric ages from the Central Valley (ka) 

Geologic unit Stratigraphically 

above unit 

(limiting 

minimum) 

Riverbank Formation-Continued 

Lower member 8103±6 

Laguna Formation 

Upper member 

Lower member 

Dacite unit 

9730 

11 2,470 

123,400±400 

Within unit 

9<730 

4

260±45 

Stratigraphically 

below unit 

(limiting 

maximum) 

11 2,470 

11 1,800 123,400±400 11 2,470 

123,400±0.400 3,200±100 

133,200±100 

2,800±300 

143,400±200 

1scc supplementary table 9 and text for full listing and discussion of 14c ages. 

2E.L. Begg, oral commun. 1982. 

Inferred correlation 

to NE San joaquin 

Valley (Marchand 

and Allwardt, 1981) 

Riverbank Formation 

middle unit 

Laguna Formation 

upper unit 

Laguna Formation 

lower unit 

No correlative unit 

Remarks Chronosequence 

soils, this 

study 

Alluvium of middle member HON-17 

on Honcut Creek has 

normal magnetic polarity 

and thus is less than about 

730 ka. 

Correlation with members 

of Laguna Formation in 

Merced River area must 

be considered tentative. 

We consider inversion 

of dates within and 

below this unit to be 

analytical, not stratigraphic, uncertainty. 

This unit underlies 

all upper Cenozoic 

alluvial units in 

Feather-Yuba Rivers area. 

HON-18 

HON-19 

HON-20 

not 

sampled 

HON-21 

HON-22 

not 

sampled 

1 OMa is millions of years before pre<;ent. 

Age of surfaces 

assumed for 

chronosequence 

(ka) 

250 

1,600 

Uncertainty 

of age 

estimates (ka), 

comments 

100-450 

0.9-3.2 Ma, 10 

normal polarity 

of uppermost gravel 

bed may be associated 

with Jaramillo (0.9 Ma) 

or Olduvai (1.8 Ma) 

normal-polarity subchron; 

see text for complete 

discussion. 

ca. 0.5-3.2 Ma, age of 

1.6 Ma for chronosequence soil proflle is 

derived from estimate of 

total time surface has 

been exposed to soil 

development 3.2 to 2.6 

m.y. and ca. 1.0 m.y. to 

the present. 

ca. 0.5-3.2 Ma 

3Carbon-14 age of 605±45 yr B.P. obtained fran wood collected at 1.2 m depth at site HON-4. 

~arden (1987). 

11Currently accepted ages of the Olduvai subchron and Gauss-Matuyama boundary (Mankinen and Dalrymple, 

1979) with which we associate the normal polarity of the uppermost gravel bed and the prominent reverse over 

normal ~larity zonation in the upper member, respectively. 

5None available from immediate project area. 

6 Atwater and others (1986). 7Marchand and Allwardt (1981). 

8Hansen and Begg (1970); American River area. 

9see text for discussion. Normal magnetic polarity in the lower member, along with stratigraphic relationships, 

suggest an age <730 ka, the currently accepted age of the Matuyama-Brunhes reversal (Mankinen and Dalrymple, 1979). 

1 Published age of the tuff at Bear Creek Falls (Evemden and others, 1964) to which the exposures of the 

Nomlaki Tuff Member of the Laguna Formation in the Oroville area have been correlated. 13Whole-rock K-Ar age on dacite; see supplementary table 9. 14Range of five K-Ar ages on biotite or hornblende from dacite; see supplementary table 9. 
Basin Deposits 

Clay-rich alluvium forms sheetlike basin deposits to the 

west of the Feather River and extends beyond the project 

area into the Butte and Sutter basins. The clays, which are 

flood-basin sediments, were deposited from major distributary channels that splay away from the Feather River (fig. 

2), and from local intermittent streams that drain land 

underlain by the Modesto, Riverbank, and Laguna Formations to the west and northwest of the Feather River. The 

basin deposits are 1 to 2 m thick in the project area and 

thicken gradually to the west. The surface is smooth and 

slopes to the west-southwest at approximately 1 m/km. 

Clay, silty clay, and minor lenses of sand and fine 

gravel compose the deposits. Exposure is poor. Dark-brown 

to black Vertisol soil profiles have formed on the deposits in 

most places. 

The stratigraphic relationship of the basin deposits to 

other units is known only from a limited number of shallow 

exposures. We have observed that (1) the upper part of the 

basin deposit overlies a conspicuous silt substratum within 

the lower member of the Modesto Formation; (2) the upper 

part of the basin deposit interfingers with the part of the 

lower member of the Modesto Formation that lies above the 

silt layer; (3) in years with heavy stream runoff before flood 

control structures were built on the Feather and Yuba 

Rivers, the basin received flood water and sediment from 

intermittent streams and distributary channels (Carpenter 

and others, 1926). The upper part of the basin deposits lap 

onto dissected surfaces of the Riverbank and Laguna 

Formations. InT. 19 N., R. 2 E., to the east of Richvale 

(fig. 2), the basin deposits bury a truncated remnant of a 

hardpan soil formed on the Riverbank Formation. From this 

we conclude that the basin deposits interfinger with at least 

the deposits of the Modesto Formation and Holocene 

alluvium. We speculate that farther to the west and deeper 

in the subsurface, the lower part of the the basin deposits 

may also interfinger with the alluvium of the Riverbank and 

Laguna Formations. 

We have no radiometric ages on the basin deposits. The 

near- surface part of the deposits can be no older than the 

age of the lower member of Modesto Formation, because 

basin clay overlies the silt substratum in the lower member. 

The top of the deposits is probably of modem age, having 

received deposition of sediment in recorded time. Basin 

sediments may well have been filling the Butte and Sutter 

·basins intermittently at least from the late Pleistocene, and 

likely from the late Pliocene to the present (Olmsted and 

Davis, 1961). 

Holocene Alluvium 

Alluvium that postdates the Modesto Formation deposits is confined to narrow flood plains along the Feather and 

Yuba Rivers and along Honcut Creek. The deposits are 

inset into channels that were cut into the Modesto and older 

formations; in the project area Holocene alluvium does not 

G14 Soil Chronosequences in the Western United States 

expand into extensive fan-shaped flood plains comparable 

to those of the older formations. We did not subdivide the 

Holocene deposits, although multiple topographic surfaces 

exist in some areas, and radiometric dating indicates age 

differences. On the Feather River, the alluvium forms a 

flood plain 1 to 2 km wide that lies 2 to 6 m below adjacent 

surfaces of older deposits. On the average, the main, broad 

Holocene flood plain lies 6 m above the low flow level of 

the river. In this reach of the Feather River, there is little 

evidence of natural levee deposits of Holocene age on the 

edge of the terraces of the lower member of the Modesto 

Formation, indicating that before debris from hydraulic 

mining altered the flow regime, the Feather River did not 

regularly send floodwaters to the west across the lower 

Modesto surface into the Butte basin. The Holocene flood 

plain of the Feather River is hummocky and deeply channeled; backfilled meander loops share the flood plain with 

anastomosing interdistributary channels in various stages of 

activity. A bluff exposure in the county park due east of the 

town of Live Oak, on the boundary between T. 16 N. and 

T. 17 N. (fig. 2), displays an 8-m-thick section of largescale trough-crossbedded sand, overlain by flat-bedded, 

finely interstratified sand and silt. The crossbed sets have 

amplitudes of 1 to 3 m. The crossbedded sand is underlain 

by coarse gravel to the base of the exposure. We interpret 

this sequence as a gravel channel and sandy point bar 

deposit of lateral accretion that is topped by a stratified 

overbank deposit of vertical accretion. Holocene deposits 

on Honcut Creek and smaller creeks consist of interstratified sand, gravel, and silt that have cut-and-fill and crosscutting channel-fill structures. 

On Honcut Creek the Holocene alluvium is less extensive; it fills channels cut across and into the flood plain of 

upper member of the Modesto Formation (fig. 3A). At the 

upper end of the Honcut Creek flood plain, Holocene 

alluvium lies in discrete, narrow channels cut into the flood 

plain of the upper member. Downstream to the confluence 

of the Feather River, natural levee and overbank deposits of 

Holocene age progressively bury the alluvium of the upper 

member of the Modesto. 

Interpretation of the distribution of Holocene deposits 

on the Yuba River is difficult, because most of the Holocene flood plain and flood plain of the upper member of 

the Modesto Formation have been destroyed either by 

mining activity or, in the Yuba River basin, by being buried 

under several meters of debris from hydraulic mining. 

The Holocene sediments are of mixed mineralogy. 

Those on the Feather River are micaceous with nearly equal 

amounts of quartz, feldspar, and lithic grains. The sediments on Honcut Creek are not micaceous and generally are 

reddish brown rather than brown or gray, which characterizes the Feather and Yuba River sediments. The Holocene 

deposits of the Feather River flood plain are at least 8 m 

thick, although they may be much thicker. On Honcut 

Creek, channel deposits are less than 3 m thick, and 

overbank sediments are no more than 1 to 2 m thick. On 
intermittent streams that drain the low foothills and older 

terraces, the Holocene sediments are red because they are 

reworked from older deposits. They range in thickness from 

1 to 2m. 

Soil landscapes 

Soils formed in Holocene alluvium of Honcut Creek are 

simple ones that have developed only A horizons. The 

Honcut soil series (Typic Xerorthents) is an example. On 

the Feather River, dominant soils of the Holocene flood 

plain are the medium-textured Columbia soils (Aquic Xerojluvents). They occur generally in a high flood plain or 

overbank position, and the coarse-textured Tujunga soils 

(Typic Xeropsamments) occur slightly above but adjacent to 

active channels of the Feather River. From site to site, 

differences in thickness of A horizons and in depth of 

mixing (biologic churning) of stratified materials are common in the Honcut, Columbia, and Tujunga soils, and the 

variations are related to differences in the age of individual 

A 

w 

..... :'a~·~;~~=·~~~:~;·~~~;. ;~·mnant of soil of Qrl 0 

B 

s 

E 

6 METERS 

0 

1000 METERS 

W E 

Soil of Oml 

c 

Figure 3. Schematic cross sections on and south of Honcut 

Creek. Vertical and horizontal scales are approximate; see 

figure 2 for explanation. A, Overbank deposits (Qa) cut 

into and overlie deposits of the upper member of the 

Modesto Formation (Qmu) on Honcut Creek. 8, Stratigraphic relations between lower member of Modesto 

Formation (Qml), upper (Qru) and lower (Qrl) members 

of the Riverbank Formation, and surface and buried soils. 

C, Reconstruction from series of backhoe trenches of 

lower member of Modesto Formation (Qml) and lower 

member of Riverbank Formation (Qrl) in SW1f4 sec. 1, T. 16 

N., R. 3 E., south of Honcut Creek. 

deposits, channels, and flood plain levels, and to the 

relative stability of particular sites with respect to continued 

deposition. Buried A horizons are also common within the 

flood plain deposits. 

Geochronology and Correlation 

The ages of Holocene deposits in the project area were 

deduced from radiocarbon dating of wood and charcoal 

samples collected on Honcut Creek and the Feather River. 

The ages range from 3,020± 160 yr B.P. to 450±45 yr B.P. 

The ages may represent true fluctuations in Holocene 

alluvial activity, random sampling of more or less continuous activity throughout the Holocene, or older charcoal 

and wood reworked into younger strata. 

The oldest age, 3,020±160 yr B.P., came from charcoal collected by Gene Begg 1. 6 m beneath a soil of the 

Columbia series on the prominent high flood plain of the 

Feather River northeast of Gridley (fig. 2, sec. 28, T. 18 

N., R. 3 E.) (E.L. Begg, oral commun., 1982). Based on 

age, extensiveness of the deposit, and geomorphic position, 

the major flood plain surface of the Feather River is here 

correlated with the post-Modesto II terrace-flood plain deposit of Marchand and Allwardt (1981) in the northeastern 

San Joaquin Valley. 

The oldest ages of 1,775±110 and 1,625±90 yr B.P. 

on Honcut Creek are from charcoal found 47 em beneath 

stratified sand on upper South Honcut Creek and from a 

burned stump at a depth of 2.5 m beneath the surface farther 

downstream. 

Charcoal fragments from depths of 1. 8 and 1 m on the 

Honcut Creek flood plain gave ages of 1 ,045 ± 95 and 

1,110±95 yr B.P., respectively. Four additional samples 

collected from three other locations on Honcut Creek gave 

ages of 450±45, 595±70 (2 dates), and 605±45 yr B.P. 

The fragment of wood that yielded the age of 605 yr B.P. 

was collected 1. 2 m beneath the surface of a natural levee 

that was the sampling site for one of the soils of the 

chronosequence, a Honcut series soil (Typic Xerorthents), 

sampling site HON-4. 

The deposits from which these charcoal and wood 

fragments were taken have a well-preserved constructional 

form of natural levees and back-levee depressions, and they 

are well vegetated and have weak soils developed on them. 

They are part of the modern flood plain but stand slightly 

above the active channels and bars. Based on the radiocarbon ages and geomorphic position, these deposits on 

Honcut Creek are broadly correlative with the post-Modesto 

III deposits of Marchand and Allwardt (1981). 

The Holocene channel fills of Honcut Creek that gave 

ages of 1,775 to 450 yr B.P. are incised into the upper, 

channeled surface of the major Feather River flood plain 

terrace, implying that the dominant episode of flood plain 

building on the Feather River took place as much as 3,000 

yr ago and that this major deposit has been modified by 

channeling of its surface since about 1, 700 yr ago. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G15 
Modesto Formation 

The deposits of the Modesto Formation are present in 

the project area as a set of little-dissected fan-shaped flood 

plains. The sediments of the Modesto Formation are asymmetric (fig. 2) in plan view because they were deposited by 

both the south-flowing Feather River and by southwestflowing distributary flood channels that drain to the Butte 

and Sutter basins. Near the mountain front at Oroville, on 

Honcut Creek, and on the Yuba River, Modesto deposits 

are inset as terraces into and topographically below the 

Riverbank Formation and older formations. Deposits of the 

Modesto Formation are, in tum, incised by Holocene 

streams and rivers and locally are buried by Holocene 

sediments. Farther west of the mountain front, the deposits 

of the Modesto Formation spread into fan-shaped flood 

plains that progressively bury sediments and soils of the 

Riverbank Formation. Extensive agricultural development, 

particularly the planting of orchards, has taken place on the 

young, fertile soils of the Modesto Formation. 

We recognized the Modesto Formation by its wellpreserved fan-shaped flood plain form, by minimal erosional dissection and minimal development of surface 

drainage channels, by its close association with modem 

streams and rivers, by its slight to moderate soil development, and by stratigraphic position. The formation has been 

divided into an upper and lower member. The lower 

member is by far the more extensive in the project area. 

Upper Member 

The upper member of the Modesto Formation is not . 

extensive in the project area; the largest remnants lie along 

Honcut Creek and the small intermittent streams that drain 

the terrace lands and low foothills. On the Feather River, 

the bulk of the upper member must have been deposited on 

a confined flood plain that was inset into the deposits of the 

lower member of the Modesto. During Holocene time, the 

Feather River seems to have reoccupied and enlarged this 

confined flood plain of the upper member of the Modesto 

Formation, and deposits of the upper member were largely 

removed in this process. Little, if any, of the alluvium or 

soils of the upper member were preserved in this scouring, 

and as a consequence we did not find deposits of the upper 

member along the Feather River itself. A large area adjacent 

to the Feather River southwest of Oroville that may have 

contained deposits of the upper member at one time was 

dredged long ago for gold. Deposits of the upper member 

are partly preserved beneath a thin veneer of young alluvium that is inset 3 m below the depositional surface of the 

lower member near the crossing of Highway 70 over 

Honcut Creek (sees. 23 and 24, T. 17 N., R. 3 E. Honcut 

7 .5-minute quadrangle). Several kilometers upstream on 

Honcut Creek, deposits of the upper member are more 

extensive and are little dissected. 

G16 Soil Chronosequences in the Western United States 

The areas along the Yuba River which most logically 

would have contained deposits of the upper member either 

have been dredged for gold or are covered by several meters 

of debris from hydraulic mining. 

On lower Honcut Creek (sees. 23 and 24, T. 17 N., R. 

3 E.) there is a conspicuous abandoned oxbow meander 

loop that was formed during a period of downcutting which 

must have occurred between deposition of the lower and 

upper members. Rapid downcutting by the Feather River, 

perhaps during interglacial time, apparently led to an 

oversteepening of the gradient on lower Honcut Creek. This 

downcutting in tum may have resulted in entrenchment of 

the meander on Honcut Creek near its confluence with the 

Feather River. Alluvium of the upper member then backfilled the abandoned meander. 

The upper member is primarily composed of fine silt 

and silty fine sand on Honcut Creek. Gravel that we 

associate with a basal channel of the upper member was 

encountered at a depth of 3. 5 m beneath the flood plain 

surface. Assuming that the deep gravel represents a basal 

channel, the upper member on Honcut Creek is 4 to 5 m or 

more thick. Because of erosion and mining activity, little is 

known of the thickness or extent of the upper member on 

the Feather or Yuba Rivers. 

Lower Member 

The lower member of the Modesto Formation consists 

of alluvial and possible lacustrine sediments deposited by 

the Feather and Yuba Rivers, by Honcut Creek and intermittent streams draining the terrace lands and low foothills, 

and by distributary flood channels that diverted flood-stage 

overbank flows of the Feather River to the west into the 

Sutter and Butte basins. We were able to recognize and map 

separately these relict distributary channels because of their 

preserved channel form, their coarse-textured sediments, 

and their characteristic soil profile development (fig. 2). 

The lower member of the Modesto Formation is extensive in the project area. The relative youth of the deposit is 

attested to by the lack of erosional dissection of its surface, 

which contrasts strongly with the moderate to extensive 

dissection of all older deposits: between Marysville and 

Honcut Creek, in a distance of 15 km, only one intermittent 

stream channel cuts its surface (sees. 1 and 2, T. 16 N., R. 

3 E., and sec. 35, T. 17 N., R. 3 E., Honcut 7.5-minute 

quadrangle). To the west of the Feather River, the smooth 

surface of the lower member is interrupted only by the slight 

undulations of the relict distributary channels. The lower 

member of the Modesto Formation is inset into older 

deposits near the mountain front and spreads into a fanshaped flood plain that flanks the Feather and Yuba Rivers 

and also extends westward into the Sutter and Butte basins 

(fig. 2). 

Along the Feather River from Oroville to the settlement 

of Oak Grove, remnants of the lower member of the 

Modesto are inset into the older deposits. The surface on 
which the older part of Oroville is located (SE corner sec. 7 

and NE corner sec. 18, T. 19 N., R. 4 E., Oroville 

7 .5-minute quadrangle) is underlain by a probable remnant 

of the lower· member, although this land was dredged for 

gold in the late 1800's. Near Oak Grove (NWI/4 sec. 11, T. 

18 N., R. 3 E., Palermo 7.5-minute quadrangle) a small 

remnant of the lower member of the Modesto is inset 

approximately 3 m below the surface of the middle member 

of the Riverbank Formation. 

On the upper part of Honcut Creek, only a single 

outcrop of probable alluvium of the lower member of the 

Modesto was found (near WI/4 corner sec. 22, T. 17 N., R. 

4 E. Honcut 7 .5-minute quadrangle) where it nestles against 

the upstream side of a remnant of the Riverbank Formation, 

which presumably protected it from erosion and removal. 

This outcrop of alluvium of the lower member of the 

Modesto lies 2 m below the surface of the Riverbank 

remnant and 1 m above the surface of the upper member of 

the Modesto Formation. The lower member appears to have 

been poorly preserved on the upper part of Honcut Creek 

because incision and lateral planation during late Modesto 

and Holocene time scoured out the flood plain to its contacts 

with the Riverbank Formation on the north and south. The 

distribution of the lower member of the Modesto Formation 

on the Yuba River near the mountain front is unknown 

because of gold dredging and overwash from hydraulic 

mining. 

Downstream on the Feather River from Oak Grove to 

Marysville and westward into the Butte basin, alluvium of 

the lower member of the Modesto spreads as a sheet that 

thickens and progressively buries the older units. Along the 

east side of the Feather River in this reach, the lower 

member of the Modesto overlies the upper and lower 

members of the Riverbank Formation in a very slight 

unconformity. A topographic break of 1 to 2 m separates the 

deposits between Oak Grove and Honcut Creek. No discernible topographic break separates the two formations 

south of Honcut Creek; there the boundary is recognized by 

strongly contrasting soil properties. 

In some places around and to the north of Honcut Creek 

(for example, near theSE corner sec. 13, T. 17 N., R. 3 E., 

Honcut 7 .5-minute quadrangle), alluvium of the lower 

member of the Modesto overlies the eroded remnants of a 

duripan soil formed on the upper member of the Riverbank 

Formation (fig. 38). Along Honcut Creek and in backhoe 

trench exposures to the, south (for example, SW1i4 sec. 24, 

T. 17 N., R. 3 E., and SWI/4 sec. 1, T. 16 N., R. 3 E., 

Honcut 7 .5-minute quadrangle), the lower member of the 

Modesto Formation unconformably overlies the soil profile 

formed on the middle member of the Riverbank Formation 

(fig. 38, C) at depths of 2 to 3 m. The Modesto Formation 

progressively buries the Riverbank Formation to the west of 

the Feather River; Modesto age and younger alluvium must 

thicken substantially to the west and southwest, because we 

found no trace of the buried soils on the Riverbank 

Formation in excavations as deep as 6 m. Davis and 

Olmsted (1952) showed brown and crumbly red zones at 

depths of 10 to 20 m at several points along a north-south 

cross section of well logs drawn between the towns of Live 

Oak and Marysville. We interpret these as a soil or soils on 

the buried surfaces of the Riverbank Formation to the west 

of the Feather River. 

Sediments in the lower member are unweathered and 

grains are subangular; those from the Feather River are 

micaceous. Quartz, feldspar, and lithic fragments dominate 

in the sand. Coarse-sand lenses commonly carry a few 

percent of fine gravel; the gravel is dominated by a blue, 

siliceous metamorphic rock. Modesto age sand from the 

Feather and Yuba Rivers is neutral gray below the zone of 

pedogenic alteration. 

A layer of compact silt forms a very prominent marker 

of uniform thickness within the lower member. The silt is 

light gray and micaceous, and from petrographic analysis 

consists of more than 70 percent silt-size aggregates of 

birefringent clay (Dennis Lytle, oral commun. of the result 

of petrographic analysis by the Soil Conservation Service, 

Lincoln Laboratories, 1981). The clay is not pedogenic but 

is primary in the deposit. The balance of the silt fraction 

consists of fresh quartz, feldspars, and ferromagnesian 

minerals. The silt is compact and very hard, but no 

cementing agent has been recognized; it is referred to as 

''hardpan'' by local orchardists although it is not a pedogenic feature. It breaks with blocky fracture and, in most 

places, it has many fine tubular pores that may be former 

root channels or insect burrows formed soon after deposition. The silt occurs as a sheet, or in sheetlike form, over an 

area of more than 390 km2 in Butte, Sutter, and Yuba 

Counties. The silt sheet is encountered at depths of 1 to 2m 

beneath the surface of the fan-shaped flood plain of the 

lower member of the Modesto (fig. 3C), and although it 

thickens and thins locally, it has an average thickness of 1 

to 2 m. It can be traced to the west, where it is interstratified 

in the clays of the Sutter and Butte basins. The stratum 

contains micaceous fine- or medium-grained sand or silty 

sand near its base, and it fines upward to a very compact 

clayey silt. The uniform thickness over a wide area and the 

upward fining of texture suggest that this is the deposit of a 

single, large flood event that spread out over the entire flood 

plain. The silt overlies sandy distributary channel and 

overbank deposits, and is in turn overlain by channel and 

overbank materials (fig. 3C). The processes of flood plain 

accretion apparently were going on before and continued 

after the postulated flood event. 

Cordell Durrell recognized a thick sequence of glacial 

lacustrine deposits of probable late Pleistocene age in 

Mohawk Valley at high elevation in the upper Feather River 

basin, and he gathered evidence that the lake was catastrophically breached and drained (Durrell, oral commun., 

1981). The relationship of the lacustrine deposits to two sets 

of Wisconsin age moraines is not clear, but the strand lines 

of the lake may cut the older moraines but not the younger 

ones. If so, breaching of the low natural dam that imLate Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G17 
pounded the lake may have taken place after the maximum 

advance of the older (Tahoe) glaciation. The lake may not 

have existed at the time of the younger (Tioga) glacial 

advance. It is a speculative but intriguing possibility that the 

silt sheet resulted directly from the breaching of a glacial 

Lake Mohawk. 

Alternatively, the silt may have been deposited as a 

lacustrine or prodelta facies of the prograding alluvial fan of 

the lower member of the Modesto Formation on the Feather 

River. Cherven ( 1984) has proposed such an explanation for 

the widespread occurrence of finely bedded silt on the distal 

parts of several ages of Pleistocene alluvial fans in the 

eastern San Joaquin Valley. Cherven explained the apparent 

coarsening upward from silt to sand to gravel within these 

alluvial deposits, noted by Marchand and Allwardt (1981), 

as resulting from westward progradation of glacial outwash 

fans into pro glacial lakes. Our observation of laminated silt 

and apparent coarsening upward of alluvium in not only the 

lower member of the Modesto but also in the Riverbank and 

Laguna Formations lends support to Cherven's explanation 

of the origin of the laminated silt. 

A second unusual feature is the relict distributary 

channels on the surface of the fan-shaped flood plain of the 

lower member of the Modesto. In many cases, the channels 

have retained their surface form, including natural levees 

and channel beds, even though these features may have 

formed on a flood plain that was abandoned as much as 

40,000 years ago. Some of the best preserved channels do 

have a thin veneer of fresh sand, but this was probably 

deposited around the tum of the century, .after sediment 

from hydraulic mining had raised the bed of the Feather 

River more than 4 mat Yuba City (Lindgren, 1911, p. 17). 

Lindgren ( 1911) stated that before mining debris raised the 

river bed, the Feather River was not subject to widespread 

overflow except at a point below Yuba City. Even today, 

after sedimentation, the surface of the flood plain of the 

lower member of the Modesto lies 7. 5 to 9 m above the 

low-flow level of the Feather River. The distributary 

channels appear not to have carried floodstage flows from 

the Feather River since early Modesto time. This conclusion 

is strengthened by the observation that soil profiles with 

strong cambic, or weak argillic horizons (Live Oa.k series 

Typic Haploxerolls, or Ryer series coarse variant, Typic 

Haploxerolls) have formed in the sandy materials both on 

the levees and in the bottoms of the relict channels. Stability 

and nondeposition (or very rare deposition) are required for 

such soils to have formed. In this case, the channels must 

have carried principally surface runoff from the local area of 

the surface of the lower member itself since the time that it 

ceased functioning as an active flood plain. The wellpreserved form also suggests that eolian deposition onto this 

surface has been minimal since the channels were formed. 

All of the sediments of the lower member that we 

observed are stratified sand and silt deposited as overbank 

sediments or in distributary channels. The distributary 

G18 Soil Chronosequences in the Western United States 

channels of the lower member of the Modesto radiate from 

the axis of the present-day Feather River. Based on these 

observations, we suggest that the north-south course of the 

Feather River, paralleling the mountain front, had been 

established by early Modesto time, and that the Feather 

River has followed essentially the same course from that 

time to the present. 

Soil landscapes 

We have informally designated soils formed on the 

upper member of the Modesto Formation on the flood plain 

of Honcut Creek as Wyman variant soils (Typic Haploxerolls) (table 2). They have brown (7 .5YR 5/40) loam or 

silt loam A horizons and cambic B horizons with strong 

brown (7 .5YR 4/6 and 5/50) colors, strong blocky structure, and a very small increase in pedogenic clay (less than 

1 to 2 percent absolute). Parent material color is 10YR 

4/3M and 6/30. 

Soils formed on the lower member of the Modesto 

Formation are quite variable laterally across the landscape, 

and they have been difficult to map accurately. The widespread compact silt substratum within this deposit (fig. 3C) 

has impeded vertical water movement in the soil profile. At 

least two distinct soil profiles can be recognized in alluvium 

containing the substratum. The Ryer series (Mollie 

Haploxeralfs) 2 soil profiles have brown or pale-brown 

(10YR 5/3 or 6/30) loam or clay loam A horizons that 

overlie yellowish-brown (lOYR 5/40), strong angular 

blocky clay loam or clay argillic B horizons. The argillic 

horizons of the Ryer soils display a net increase in clay of 

up to 12 percent. Phases of this soil have been delineated 

during soil-survey mapping (see table 6) based on differences in surface texture and depth to the silt substratum. A 

second distinct soil has formed over the substratum where 

internal drainage has been further impeded. The Ryer 

duripan variants (Abruptic Durixeralfs) have similar features in the upper profile to those of the Ryer series, but 

argillic horizons are more clay rich and are underlain by 

light yellowish-brown (10YR 6/40) silica- and calcium 

carbonate-cemented duripans formed near the interface with 

the substratum, Parts of the soil landscape that lack the silt 

substratum display less strongly developed soils of the 

Wyman series {Mollie Haploxeralfs)3 with brown (10YR 

5/30) loam A horizons overlying brown (7 .5YR 5/40) clay 

loam argillic B horizons that have an average net increase in 

pedogenic clay of 5 or 6 percent. In addition, small areas of 

soils on the lower member, usually associated with the 

Wyman series, have little or no increase in clay content 

from the A to the B horizon, and therefore are similar to the 

2 This is the series classification assigned in the Yuba area soil survey. 

While it is probably correct, it is at variance with the official series 

classification for Ryer, which is Typic Halploxeralfs. 3 This is the series classification assigned in the Yuba area soil survey; 

the official Wyman series classification is Typic Haploxeralfs. 
Wyman variant soils of the upper member of the Modesto 

Formation. In general, these more weakly developed soils 

occur near the Feather River (D. Lytle, oral commun., 

1982). Although there is no topographic evidence, it is 

possible that areas of the terrace of the lower member of the 

Modesto near the river were subject to scour and erosion to 

a depth of less than 1 m after early Modesto time, and were 

subsequently backfilled to an accordant level. 

We have informally designated soils formed on coarse 

distributary channel deposits of the lower member of the 

Modesto Formation as Ryer coarse variants (Typic Haploxerolls). These soils display just less than the 3 percent 

absolute increase in clay content required to meet the 

definition of an argillic horizon set forth in Soil Taxonomy 

(Soil Survey Staff, 1975), yet they have all the evidence of 

argillic character. The soils have brown (7 .5YR 5/2D) 

sandy loam A horizons with about 10 percent clay, and 

brown to strong brown (7 .5YR 5/4 to 5/5D) argillic horizons that have about 13 percent clay, abundant clay films 

bridging grains and coating pebbles, and moderate angular 

blocky structure. On the soil-geomorphic surface of the 

lower member of the Modesto Formation, soils range from 

weakly developed on coarse, somewhat excessively drained 

materials, to moderately strongly developed with duripans 

and strong argillic horizons on finer, silt loam and clay loam 

parent materials that overlie a restrictive substratum. 

Geochronology and Correlation 

We recognize and differentiate two members of the 

Modesto Formation in the project area based on stratigraphic relations and differences in soil development. We 

have correlated these units with the two members of the 

Modesto Formation in the northeastern San Joaquin Valley 

(Marchand and Allwardt, 1981) by tracing similar geomorphic surfaces from the project area to the Sacramento area, 

and by comparison of soil profile characteristics between 

areas. 

The ages of the two members of the Modesto Formation were not determined in the project area; no datable 

materials were found even though a great deal of time was 

spent searching natural and manmade exposures. Marchand 

and Allwardt (1981) and Harden (1987) summarized available radiometric ages of the two members: The upper 

member of the Modesto Formation is bracketed by radiocarbon ages from the San Joaquin Valley of about 8 to 9 ka 

and 27 to 31 ka (Atwater and others, 1986). Marchand and 

Allwardt (1981) and Harden (1987) associated deposition of 

alluvium of the upper member· of the Modesto Formation 

with the Tioga glaciation in the Sierra Nevada, which ended 

by about 9,000 years ago. The close association of the 

upper member of the Modesto Formation with Holocene 

channels on Honcut Creek, the total absence of surface 

dissection, and the relatively undeveloped soils on the 

member suggest that the age of the surface of the deposit is 

in the young end of this range of ages. Pending radiocarbon 

dating of the upper member in the project area, we have 

adopted an age of 10 ka for the upper part and soils of the 

upper member (table 3). 

The age of the lower member of the Modesto Formation is not well established. Marchand and Allwardt (1981) 

pointed out that deposits correlated with the lower member 

could represent two episodes of alluvial deposition in early 

and middle Wisconsin time. Marchand and Allwardt (1981) 

reported a uranium-series age on bone of about 29 ka as a 

probable minimum age for the lower member, and they 

cited a radiocarbon age of 42.4 ka from wood near the base 

of the lower member. Harden (1987) revised uranium-trend 

ages, reported by Marchand as 95±45 ka, to about 42 ka 

using new calibrations. Atwater and others (1986) estimated 

the age of the lower member of the Modesto Formation at 

20 to 26 ka based on work in the southern San Joaquin 

Valley. We have adopted a tentative age of 40 ka for the 

upper surface and soils of the lower member, although the 

deposit has not been dated in the project area; the true age 

may range from 14 to 100 ka (table 3). 

Riverbank Formation 

The Riverbank Formation underlies a prominent, rolling, moderately dissected landscape that occurs as a belt 

along the valley margin between the high terraces to the east 

and Modesto Formation to the west. Remnants of the 

Riverbank Formation are inset into deposits of the Laguna 

Formation near the mountain front on the Feather and Yuba 

Rivers. To the west and southwest, alluvium of the Riverbank Formation spreads out to form a fan flood plain, now 

dissected, that buries the eroded surface of the Laguna 

Formation. The Modesto Formation deposits, in tum, bury 

the surfaces and soils formed on the Riverbank Formation. 

We subdivided the Riverbank Formation in the project area 

into two members on the basis of stratigraphic superposition, geomorphic expression, and surface and buried soils. 

We have named these the upper and lower members of the 

Riverbank Formation, and correlate these deposits with the 

upper and middle units, respectively, of the Riverbank 

Formation in the northeastern San Joaquin Valley (Marchand and Allwardt, 1981). We do not recognize the lower 

unit of the Riverbank Formation of Marchand and Allwardt 

(1981) in the project area. 

The relationship between the two members of the 

Riverbank Formation over most of the project area is one in 

which alluvium of the upper member is inset into and 

topographically below high remnants of the rolling, dissected surface of the lower member. This results in a pattern 

of ''islands'' of the lower member that project 1 to 5 m 

topographically above the surface of the upper member. 

The dual surfaces of the Riverbank Formation are well 

expressed on Honcut Creek near the town of Honcut and on 

the Feather River to the east and southeast of Oak Grove. At 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G19 
these places the topographic separation of the two members 

is about 5 m. The topographic separation of the members 

diminishes to the south on the Feather River and to the west 

on Honcut Creek, because the lower member dips more 

steeply to the west-southwest than does the younger upper 

member. Just to the north and east of the confluence of the 

Feather River and Honcut Creek, the separation is about 1 

m, and to the south of Honcut Creek the upper member 

overtops and buries the lower member. This pattern is 

difficult to confirm on the Feather River above Oak Grove, 

and on the upper Yuba River, because very little Riverbankage alluvium has been preserved along their channels, both 

of which have been deeply incised into the high terraces of 

the Laguna Formation. 

The rolling surfaces of the Riverbank Formation can be 

traced at least as far south as Sacramento County. The soils 

formed on the Riverbank are locally referred to as "red 

clays" because of their strong, brightly colored argillic B 

horizons. Until recent years, these lands were dry-farmed to 

wheat and barley, but today they are being leveled to grow 

irrigated rice. 

Upper Member 

The upper member of the Riverbank Formation is most 

extensive to the east of the Feather River between the towns 

of Palermo and Honcut, and south from there to the Yuba 

River. To the west of the Feather River most of the upper 

member of the Riverbank Formation has been buried by 

alluvium of the Modesto Formation; however, small areas 

of the upper member of the Riverbank crop out to the east 

and northeast of the town of Biggs (fig. 2). 

The upper member of the· Riverbank Formation was 

deposited over a wide area as a veneer 1 to 3m thick on the 

rolling, dissected surface of the lower member of the 

Riverbank. This veneer is generally composed of silt and 

sand. Coarser sandy and gravelly deposits greater than 3m 

thick were found adjacent to the modem .Honcut Creek. 

The upper member of the Riverbank is separated from 

the lower member in some places by a buried soil on the 

surface of the lower member. For example, a buried soil on 

the lower member can be seen in the channel of Honcut 

Creek (SEI/4NEI/4 sec. 19, T. 17 N., R. 4 E., Honcut 

7 .5-minute quadrangle). The buried soil has some characteristics like the modem-day Alamo series (Typic Duraquails) soils which form in clayey sediments. This buried 

soil on the lower member appears to have formed in 

fine-textured sediment in a depression on an erosional 

surface that must predate deposition of the alluvium of the 

upper member. Additional evidence of an unconformity and 

hiatus between the two Riverbank members was found at 

Honcut Creek near the Highway 70 triple bridges, and in 

backhoe trenches in the Modesto Formation 4 km to the 

south (SI/2 sec. 24, T. 17 N., R. 3 E.; and NWI/4SWI/4 sec. 

1, T. 16 N., R. 3 E., respectively, Honcut 7.5-minute 

quadrangle). At these locations, part of a red argillic 

G20 Soil Chronosequences in the Western United States 

horizon is buried beneath deposits of the Modesto Formation. The soil remnant is topographically lower than the 

projection of the surface of the upper member, and we infer 

that it is a remnant of an older, stratigraphically lower, 

buried soil formed on the eroded surface of the lower 

member (fig. 3B). 

In the central area between Palermo and Honcut Creek, 

alluvium of the upper member is 1 to 2 m thick and it 

unconformably overlies a compact silt layer in the lower 

member. The soil profile that has formed on the upper 

member in this area extends through the alluvium of the 

upper member and into the silt layer in the lower member. 

A silica-cemented duripan has formed along the unconformity because of restricted water movement into the underlying silt stratum. 

The upper member of the Riverbank Formation can be 

differentiated from the lower member on the basis of degree 

of erosional dissection. Surface relief on the upper member 

averages 1 m and a partially integrated drainage pattern 

results in a subtle mound and swale topography. Small 

intermittent streams are incised as much as 2 m below the 

surface of the upper member, Honcut Creek is incised as 

much as 3m, and the Feather River is incised as much as 9 

m below the surface of the upper member. 

Lower Member 

The surface extent of the lower member of the Riverbank Formation is not as great as that of the upper member: 

it crops out discontinuously and adjoins the Laguna Formation in an arc from northeast of Biggs on the north to the 

Yuba River on the south (fig. 2). It also crops out in the 

central and south-central project area as isolated remnants 

that are surrounded by deposits of the upper member of the 

Riverbank Formation and the Modesto Formation. 

On the Feather River north of the town of Oak Grove, 

the lower member was deposited within a deep channel cut 

into deposits of the Laguna Formation. Small remnants of 

the lower member are inset against the Laguna Formation a 

few kilometers to the southeast and south of Oroville. The 

topographic separation between the surfaces of the lower 

member of the Riverbank Formation and the upper member 

of the Laguna Formation decreases from about 20 m near 

Oroville to less than 5 m near Oak Grove, because the older 

unit dips more steeply to the southwest than does the 

younger. 

Downstream from Oak Grove on the Feather River, the 

lower member of the Riverbank spread from its confining 

canyon within the Laguna Formation to form a wide 

fan-shaped flood plain which almost completely buried the 

dissected surfaces of the Laguna Formation. The remnants 

of this flood plain of the lower member occur now as the 

isolated outcrops in the central project area. To the southwest and south of Oak Grove, the lower member of the 

Riverbank Formation is in tum buried by alluvium of the 

upper member of the Riverbank Formation and of the 
Modesto Formation. On Honcut Creek and the Yuba River, 

alluvium of the lower member of the Riverbank spread to 

the west as fan-shaped flood plains from points very close to 

the mountain front. Very few remnants of the lower 

member exist in the narrow channels upstream from these 

points. Downstream or westward from the mountain front 

on these waterways, the lower member of the Riverbank 

Formation almost completely buries the dissected remnants 

of the Laguna Formation. 

The landscape of the lower member is distinctly rolling, with up to 5 m of relief. An integrated drainage 

network is well developed. The outcrop pattern of the lower 

member appears to conform more closely to the drainageways of the present-day creeks and rivers than does that of 

the Laguna Formation. 

There are few exposures in the Riverbank Formation; 

however, the reference section described below is typical of 

the lower member: 

Reference section location: South Honcut Creek; description taken at an 

exposure in the south bluff; S'/4 corner NE1

/4NE1

/4 sec. 27, T. 17 N., R. 4 

E.; Honcut 7.5-minute quadrangle. 

Elevation of top of l?luff is approximately 125 ft (37 m). 4 

Riverbank Formation: 

Lower member: 

Approximate 

thickness (m) 

4. Medium and coarse sandy clay, with occasional 

fine gravel, weathered reddish brown to red; Kimball series soil profile formed in these sediments is 

poorly exposed, hilltop convex .. .. .. .. .. .. . .. .. .. .. .. - 2.0 

3. Medium to fine subangular sand; gradational to 

overlying unit; feldspars are highly weathered; 

cross-bedded, individual cross-bed sets up to 0. 7 m 

in height; weathered brown to red brown . . . . . . . . . . 1.0 

2. Medium to coarse sand; similar to unit above but 

forms a distinct channel cut into underlying unit .. 0-1.5 

I. Silt; finely laminated and cross-laminated; very 

compact; weathered gray to buff ..................... - 2-3 

Total thickness ...................................... .5.0-7.5 

Base of bluff, stream channel underlain by modem deposits. 

The coarse overlying fine sequence is typical of the 

deposits of the lower member of the Riverbank on the 

Feather River and on Honcut Creek. 1 

The thickness of the lower member is not known 

directly; maximum exposure is about 6 m on Honcut Creek 

(description above). A driller's log from a California 

Department of Water Resources test well on Highway 99 at 

the Thermalito Afterbay (79-107A) records what may be a 

complete aggradational unit of the lower member that is 9. 5 

m thick. This was described by the geologist in charge as a 

probable fill in the eroded surface of the "Red Bluff" 

(Laguna Formation) because a distinct pumiceous tuff bed 

at 4 m in this unit is not reported in .any other nearby wells 

(R. Bartlett, California Department of Water Resources, 

oral commun., 1981). 

4 Elevations are stated in feet, with metric equivalents in parentheses, 

because topographic maps for this area use English units. 

Riverbank Formation alluvium consists largely of 

mixed, well-sorted, subangular quartz, feldspar, and lithic 

sand and silt that is similar in physical appearance to 

alluvium of the older units. Gravel is less common than in 

the older units, except locally where there has been a source 

of cobbles that are reworked from the older units. Trough 

crossbeds as much as 1 m in amplitude are present in 

Riverbank alluvium. Silt and silty sand is finely laminated 

and cross laminated. The beds of silt are very compact, and 

their appearance is that of a siltstone, although no cementing agent is obvious. The silt weathers neutral gray to light 

tan. Gravel clasts, including those of granitic composition, 

are fresher than those in the older units. 

Soil Landscapes 

Soils formed on the Riverbank Formation are deeper, 

redder, and more strongly developed than those formed on 

the Holocene alluvium and on the Modesto Formation. The 

Yokohl series (Typic Durixeralfs) duripan soils have 

reddish-brown (5YR 4/3D) loam A horizons that abruptly 

overlie reddish-brown or yellowish-red (5YR 5/4 or 5/6D) 

clay-textured argillic B horizons. The argillic horizons 

overlie strongly cemented reddish-brown (5YR 5/4D) ironand silica-cemented duripans at about 1.1 m. Yokohl series 

soils are dominant on the surfaces of the upper member of 

the Riverbank in the vicinity of the Feather River and 

Honcut Creek, where alluvium of the upper member is thin 

and overlies compact silt of the lower member. Along the 

Yuba River, the San Joaquin series (Abruptic Durixeralfs) 

replaces the Y okohl series where alluvium of the upper 

member has a larger granitic component. Soils of the 

Kimball series (Mollie Palexeralfs) are found in areas where 

the alluvium of the upper member is thicker, as near the 

town of Honcut, or where the unconformity on the alluvium 

of the lower member is not abrupt texturally. These are the 

soils that we sampled to represent soil development on the 

surface of the upper member of the Riverbank. These soils 

are quite strongly developed and they have brown or 

reddish-yellow (7 .5YR 4/4 or 6/6D) loam or silt loam A 

horizons that abruptly overlie dense, reddish-brown or 

yellowish-red (5YR 5/4 or 5/6D) claypan argillic horizons 

at about 70 em. The argillic horizons extend deeper than 1.2 

m, and transitional BCt horizons may extend as deep as 2.5 

m. Skeletans (coatings of clean sand and silt grains on the 

surfaces of prismatic or blocky peds) are well developed in 

the BA horizon of these soils, indicating strong leaching of 

the upper part of the Bt horizon probably as a result of 

lateral flow of water through these profiles from adjacent 

higher-elevation surfaces of the lower member of the 

Riverbank. The landscape of the upper member of the 

Riverbank displays as much as 1 to 2 m of relief, and a 

mound and swale microrelief is well developed on undisturbed sites. Soils of the mound areas tend to have thicker 

A and BA horizons, and locally soils of the Landlow series 

occur in swales. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G21 
Remnants of the lower member of the Riverbank 

Formation generally rise 2 to 5 m above the level of the 

landscape of the upper member. Soils on the least eroded 

surfaces of the lower member are distinctive, and we have 

informally designated them as Kimball deep variants (Mollie Palexeralfs) (table 2). These soils have argillic horizons 

that are deeper and redder than those of the Kimball series, 

although they have lower maximum clay contents than do 

the argillic horizons of the Kimball or Y okohl series formed 

on the upper member. The deep-variant soils have reddishbrown (5YR 5/4D) loam A horizons, thick transitional BA 

horizons, and red (2.5YR 5/6D) clay loam argillic horizons 

that extend from 0. 9 to 1. 6 m in the profile. These soils also 

have very thick transitional BCt horizons that extend to 3 m 

and beyond. Soils on erosional hillslopes between the lower 

and upper members of the Riverbank have properties that 

are transitional between the two Kimball soils. On the Yuba 

River, soils of the Ramona series (Typic Haploxeralfs) 

replace the Kimball deep variant in parent materials that are 

largely granitic. 

Geochronology and Correlation 

Within the local stratigraphic sequence, the two alluvial 

deposits that we correlate with the Riverbank Formation are 

distinctive and unique in several ways compared to both 

younger and older alluvial deposits. They are intermediate 

between deposits of the Modesto and Laguna Formations in 

stratigraphic position, degree of surface dissection, and 

degree of soil development. The two deposits together 

compose a distinctive geomorphic unit that has 1 to 5 m of 

rolling relief. The profile index of soils formed on these two 

deposits is significantly different from the profile indices of 

either the Modesto or Laguna Formations (see table 10). 

Within the local stratigraphic sequence, the two deposits that we correlate with the two members of the Riverbank 

Formation are separate alluvial units as shown by an 

uncor:tformable contact between them, marked by a strongly 

developed buried soil, and by differences in erosional relief. 

No radiometric ages are available from either member in the 

project area; however, we use two lines of evidence to 

establish a correlation to the type locality of the Riverbank 

Formation in the northeastern San Joaquin Valley and to 

assign probable ages for the two members. First, the 

distinctive geomorphic surface and characteristic soils of 

the Riverbank Formation can be traced from Sacramento 

County (Helley, 1979), where radiometric ages are available, into the project area. Second, the soils formed on the 

two members of the Riverbank Formation in the project area 

and at the type locations on the Merced River (Harden, 

1987) are similar in degree of soil profile development. For 

example, both the absolute values of the profile index and 

the small difference in the profile index between members 

seem characteristic of the Riverbank Formation in both 

areas (see table 10). 

G22 Soil Chronosequences in the Western United States 

Marchand and Allwardt (1981) and Huntington (1980) 

described three separate alluvial units within the Riverbank 

Formation in several areas of the eastern San Joaquin 

Valley. The oldest unit in the San Joaquin Valley is the least 

extensive of the three, and has very little preservation of 

surface form, or surface exposure (Marchand and Allwardt, 

1981). It is found primarily in the subsurface. The middle 

unit is extensive and is highly dissected (as much as 5 m of 

relief), and the upper unit, which is of intermediate extent, 

has much lower ( <2 m) relief (Marchand and Allwardt, 

1981). Shlemon (1967a, b, 1972) recognized two rather 

than three alluvial fills of Riverbank age associated with the 

ancestral American River in Sacramento County. Harwood 

and others ( 1981) and Helley and Harwood ( 1985) also 

recognized two rather than three alluvial units of the 

Riverbank Formation in the northern Sacramento Valley. 

The reason why three units were recognized in the San 

Joaquin Valley and only two in the Sacramento Valley is 

not known. Two rather than three episodes of alluviation 

may have occurred in the north because the physical 

response of the northern Sierra to Pleistocene climatic 

change and tectonism was different from that in the central 

and southern Sierra. 

We provisionally correlate the upper and lower members of the Riverbank Formation in the Feather and Yuba 

rivers area with the upper and middle units of the Riverbank 

Formation of Marchand and Allwardt (1981), respectively. 

We base this on similar degree of soil development of the 

members between areas (see table 10), on similar geomorphic expression of the members between areas, on physical 

tracing of the geomorphic surface between areas, and on 

similarities in extensiveness of the two members between 

areas. 

We have only limited information from the project area 

on the age of the Riverbank. Two oriented samples collected from the reference section of the lower member on 

Honcut Creek had normal magnetic polarities, which, in 

conjunction with stratigraphic relationships, suggests deposition during the Brunhes Normal-Polarity Chron, and an 

age of less than about 730 ka. 

Andrei Sarna-Wojcicki determined the concentration of 

major and trace elements in a sample of pumiceous sand 

from a depth of 6 m in an alluvial deposit near the perimeter 

of the Thermalito Afterbay that we correlate with the lower 

member of the Riverbank Formation. Similarity coefficients 

determined by Sarna-Wojcicki on the basis of the elemental 

suite are 0.9 for comparison of this pumice with the 

informal Rockland ash bed (0.45 Ma) and 0.85--0.9 for 

comparison with the Nomlaki Tuff member of the Tehama 

Formation (3.4 Ma). Neither coefficient is high enough to 

permit reasonable correlation with these well-known tephra 

units (A. Sarna-Wojcicki, oral commun., 1984). The eruptive source and age of the pumiceous sand are not known at 

this time. 

The age of the Riverbank Formation in the northeastern 

San Joaquin Valley is known from several lines of evi-
dence. Hansen and Begg (1970) reported a minimum age of 

103±6 ka for the younger(?) Riverbank deposits in Sacramento County. This age was based on uranium-series dating 

of mineralized vertebrate fossils. All units of the Riverbank 

Formation in the Merced River area are much younger than 

600 ka because. there was time to develop a strong soil on 

the radiometrically dated Turlock Lake Formation before 

the lower unit of the Riverbank Formation was deposited 

(Marchand and Allwardt, 1981, p. 41). 

Marchand ( 1977) correlated the three units of the 

Riverbank with marine cold-water isotope stages 6, 8, and 

10 or 12, dated at 127-190, 247-276, and 336-356 or 

425-457 ka, respectively (Hays and others, 1976). Harden 

(1987) reported uranium-trend ages of 140±40 ka and 

145±20 ka for the upper unit, and 260±45 ka for the 

middle unit of the Riverbank in the Merced River area. 

Harden also reported a uranium-trend age of 120±40 ka on 

upper member alluvium at a site near the quarry, where 

Hansen and Begg' s ( 1970) bone was recovered to yield the 

uranium-series age of 103 ka. 

The radiometric ages of the upper member from the 

Sacramento area and Merced River and the age of the end of 

oxygen-isotope stage 6 are in reasonable agreement. We 

have adopted an age of 130 ka for the upper surface of the 

upper member of the Riverbank Formation in the project 

area. We believe it is reasonable, given the similarity of the 

geomorphic surfaces and soils between the Sacramento area 

and the project area. We have adopted an age of 250 ka for 

the upper surface of the lower member. The erosional relief 

and strong soils that developed on the lower member before 

deposition of the upper member are consistent with the long 

time interval postulated between members. Because we lack 

radiometric dating of the lower member in the project area, 

we must allow the possibility that our lower member is 

correlative with the lower unit of Marchand and Allwardt 

( 1981) and has an age of 330-450 ka (correlative with the 

ends of marine cold-water isotope stages 10 or 12). 

Laguna Formation 

Deposits associated here with the Laguna Formation 

underlie the rolling, deeply dissected hills east of Oroville, 

the prominent high terraces that flank the Feather and Yuba 

Rivers at the margin of the valley, and the isolated remnants 

of high terraces that lie several kilometers west of the valley 

margin between the Feather and Yuba Rivers. 

The Laguna Formation occurs above the older dacitic 

unit, and it is truncated by a complex of erosional surfaces 

that are difficult to trace or correlate laterally. The Laguna 

Formation is unconformably overlain by the Riverbank 

Formation (fig. 4A, C). 

The Laguna Formation consists of a tuff and two 

distinct alluvial units of different ages that have a complex 

relationship to each other. The alluvial units are here 

designated the lower and upper members of the Laguna 

Formation. The Nomlaki Tuff Member, a distinctive time 

marker in the Sacramento Valley, occurs at or near the base 

of the lower member and provides the basis for correlating 

the Laguna Formation in part with the Tuscan and Tehama 

Formations, which also include the Nomlaki as a member. 

A thick gravel bed caps the upper member in most places. 

We use the informal term uppermost gravel bed for this 

layer. The formation displays relict, exhumed, and erosional surfaces that are marked by distinctive surface and 

buried soils. A complex interplay of deposition, erosion, 

and tectonics must be invoked to explain the outcrop 

patterns now seen. 

The two alluvial members of the Laguna are apparently 

superposed in normal stratigraphic order in the subsurface 

beneath the massive high terrace west and northwest of 

Oroville. Drill logs from this area show two fining-upward 

sequences above the dacitic unit. Each sequence begins 

with a basal gravel (as much as 10 m thick) and fines 

upward into stratified sand, silt, and clay. The relict surface 

of the upper member is represented by remnant knolls such 

as the hill at the Butte County Administrative Center (SWI/4 

sec. 6, T. 19 N., R. 4 E., Oroville 7.5-minute quadrangle). 

The buried surface of the lower member, just beneath the 

basal gravel of the upper member, contains what appears in 

the drill records to be a soil profile that is as thick as 6 m. 

The buried soil on the lower member is exposed at an 

elevation of 140ft (43 m) on the southwest wall of the large 

borrow pit 2 km south of the Oroville airport. The soil 

profile exposed there is more than 5 m and possibly 8 to 10 

m thick, has prominent reticulate mottling, and is similar to 

the Red Bluff strong variant surface soil (Palexerults) 

recognized on exhumed surfaces of the lower member of the 

Laguna. To the southeast, across the Feather River in the 

area between Oak Grove and Palermo, and at other sites 

such as near Honcut Creek, the upper member of the 

Laguna has been stripped away by erosion, exhuming the 

lower member (fig. 4A, C) The soil profiles seen at these 

sites vary in their properties and are the result of reexposure of remnants of the soil originally formed on the 

surface of the lower member of the Laguna before burial by 

the upper member, and of renewed soil development since 

the time of exhumation. East of Oroville and Palermo, at 

elevations of as much as 600ft (183m), dissected remnants 

of the lower member of the Laguna Formation crop out that 

were never buried by the upper member. A few hillcrests in 

this position bear relict soils that have developed over a 

span of as much as 3 million years. The area west of 

Palermo Ridge that demonstrates normal superposition of 

the two Laguna members, and the area to the east where the 

younger deposit is inset topographically below the older, 

are apparently related across a zone of monoclinal flexure or 

high-angle reverse faulting, or both, that was active at the 

time one or both members were deposited. 

It is not possible to recognize and separate the two 

alluvial members of the Laguna Formation on the basis of 

lithology alone. Their separation is based on distinct topographic position (for example, east of Oroville where the 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G23 
lower member has never been buried); on recognition of the 

unique, extremely strong relict soil profile that is preserved 

on infrequent high-elevation remnants of the lower memA 

sw 

METERS 

180 

150 

120 

90 

ber, or of the anomalously strong soil profiles displayed 

where the lower member has been exhumed by erosion of 

the upper member; and on the subsurface expression of the 

A' 

NE 

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120 

90 

60 ? ------------- ~.----- .--.---__.-

,-----::;_ _ _QTiu --------.::::::::---- 60 

30 

SEA 

LEVEL 

8 

METERS 

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Til ----

8' 

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0 1000 METERS 30 

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LEVEL 

1000METERS 

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c 

METERS 

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Figure 4. Schematic cross sections showing inferred extension of Prairie Creek (PC) and Magalia (M) lineament fault 

zones; arrows show probable direction of movement. See 

figure 2 for locations and description of map unit symbols. 

Contacts dashed where approximately located; heavy 

dash/dot line above units represents reconstructed surfaces of upper and lower members of the Laguna Formation indicating inferred monoclinal flexure; vertical exagG24 Soil Chronosequences in the Western United States 

SEA 

LEVEL 

C' 

210 

,/~ 

180 

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0 1000 METERS 30 

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LEVEL 

geration x20. A, Section A-A' showing a slope of 18 m/km 

on reconstructed Til surface and slope of 11 m/km on the 

unit g surface. B, Section 8-B' showing reconstructed 

apparent uplift of northeastern block as inferred from 

discussion of deformation. C, Section C-C' showing relations of relict, buried, and exhumed surfaces of Til and 

apparent uplift of northeastern block. 
superposition of two fining-upward alluvial cycles separated by a strongly developed buried soil. In places where 

these clues are lacking, one cannot say with certainty which 

of the two members is displayed. 

Upper Member 

The upper member of the Laguna Formation comprises 

most of the deposits underlying the rolling high terrace 

surface in the Thermalito area west of Oroville, the haystack hills and bluffs south of Oroville on Highway 70, and 

the upper part of the isolated terrace remnants between 

Honcut Creek and the Yuba River. These are the principal 

landforms that Olmsted and Davis ( 1961) correlated with 

the Laguna Formation. 

The upper and lower contacts of the upper member are 

unconformable in the map area. The base of the upper 

member rests, in various places, on metamorphic bedrock, 

on the eroded surface of the older dacite unit, and on the soil 

profile or sediments of the lower member. Relief on the 

underlying units may exceed 45 m. Basal gravel of the 

upper 'member rests on bedrock at 160 ft (50 m) elevation 

near the Feather River Fish Hatchery, but 1 km to the north, 

the upper member rests on the top of the dacite unit at 295 

ft (90 m) elevation. A valley apparently was .cut into 

sediments of the lower member and older deposits by the 

ancestral Feather River, in approximately its present position, before deposition of the upper member began. Flexure 

or faulting along the mountain front during Pliocene time 

may have controlled the erosional pattern. Near the Yuba 

River, the upper member was apparently deposited unconformably on the lower member. 

The upper member consists of fluvially deposited 

gravel, sand, and silt of mixed lithology and mineralogy. 

Beds of sand and silt appear to dominate over gravel within 

the upper member, although lateral variability is great and 

exposures are few. The composition of gravel in the upper 

member is similar to that in the lower member. Several 

types of blue silicic metamorphic rocks are common, as are 

clasts of quartzite, dark metavolcanic rocks, and a pale 

greenish-white felsic metavolcanic(?) rock. Volcanic and 

granitic rocks are generally only minor components of the 

gravel, except at a few outcrops where individual gravel 

beds carry a large proportion of andesitic cobbles. The 

gravels and cobbles are subrounded or rounded and average 

10 to 15 em in diameter, although cobbles in the basal part 

of the upper member on the Feather River and in the 

uppermost gravel bed south of the river are coarser, as much 

as 40 em in diameter. The conglomerates are matrix 

supported, and most show imbrication of the cobbles. 

Conglomerate beds encountered in the subsurface west of 

the Feather River carry mixed gravel that is 5 to 12 em in 

diameter. 

Sand in the upper member is composed of subangular 

or subrounded quartz with a high proportion of lithic grains 

and weathered feldspar. Sand tends to be fresher in the 

upper member than in the lower member. Individual sandy 

beds vary from flat and well-bedded to trough-crossbedded 

forms with amplitudes of more than 2 m. 

Finely bedded and laminated silt and clay with a 

tuffaceous appearance is interbedded with sandy beds in the 

upper member. Individual beds of silt drape over undulating 

surfaces of underlying crossbed sets. Silt beds also contain 

thin flat laminae and fine crosslaminations. 

A striking feature of the upper member of the Laguna 

Formation is the tuffaceous appearance of many sandy and 

silty beds, and the local appearance of abundant volcanic 

clasts in gravel beds. Exposures of the upper member along 

Highway 70 and in a railroad cut illustrate these lithologic 

variations (NEI/4 sec. 36, T. 19 N., R. 3 E., and NEI/4 sec. 

31, T. 19 N., R. 4 E., respectively, Palermo 7.5-minute 

quadrangle). At the Highway 70 site, individual beds in the 

section alternate between lithic volcanic sand and mixed 

sand; high in the cut, one gravel bed has abundant cobbles 

of andesite(?) in a sandy, tuffaceous matrix. At the railroad 

site, some silty beds appear to be highly weathered tuff. 

Exposures such as these have led some geologists 

(Lindgren, 1911; R. Ford, unpub. mapping) to assign these 

sediments to older volcanic units. An alternative explanation, based on the fact that these sediments were deposited 

contemporaneously with part of the volcanic activity that 

formed the Tuscan Formation to the north, is preferred. 

Volcanic mudflows did not come down the Feather River 

drainage to the Sacramento Valley, although the Tuscan 

Formation directly abuts the west branch of the Feather 

River. We propose that airfall ash, lapilli, and possibly 

volcanic blocks were deposited in, then eroded from, the 

upper watershed of the Feather River and that these became 

interbedded with the more typical mixed sediments in the 

resulting deposits. 

Because of poor exposure and lateral heterogeneity, the 

gross stratigraphy of the upper member is not well known. 

From the outcrops and drill records examined, the lower 

part of the upper member of the Laguna Formation in the 

Feather River area consists of coarse basal channel deposits 

of gravel that thicken to the west or southwest. Deep 

exposures along the north and west sides of the river, near 

where Highway 70 crosses it, show these deposits. The 

upper member here appears to have filled the deepest trough 

cut in older deposits and in bedrock. In this exposure the 

gravel is coarse, crudely bedded, and because it is more 

than 24m thick, probably represents more. than one aggradational cycle. The basal gravel lies on metavolcanic 

bedrock and on the eroded surface of the dacite unit in these 

exposures. Five kilometers to the south, in a railroad cut 

(NEI/4 sec. 31, T. 19 N., R. 4 E., Palermo 7.5-minute 

quadrangle), a coarse basal gravel bed 4 m thick rests on 

dacitic sediment. In the subsurface 10 km to the west, along 

Highway 99, a basal gravel of the upper(?) member is 9 m 

thick and rests on the buried soil of the lower member. 

In the few places where the middle section of the upper 

member is exposed, it is generally composed of crossbedlate Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G25 
ded sand and finely laminated silt or silty clay. At least two 

buried soils have been recognized in this part of the section, 

one at the Thermalito Power Plant and another in a roadcut 

on Ophir Road (NEI/4 sec. 31, T. 19 N., R. 4 E., Palermo 

7 .5-minute quadrangle). The soils are moderately to 

strongly developed, with red or reddish-brown argillic B 

horizons, and in aggregate they may represent tens to 

hundreds of thousands of years of landscape stability and 

nondeposition within the upper member. 

At several places in the Oroville area, the dissected 

surface of the upper member forms knobs or haystack hills 

that rise 10 to 20 m above the general landscape of more 

eroded parts of the upper member: the Butte County 

Administrative Center, the canal crossing at Cherokee 

bridge, and the haystack hills south of Oroville are examples (SWI/4 sec. 6, and sec. 5, Oroville 7 .5-minute quadrangle; and sees. 29 and 31, Palermo 7. 5-minute quadrangle; 

respectively, T. 19 N., R. 4 E.). These are underlain by a 

coarse gravel lag or channel deposit that appears to be the 

uppermost bed of the upper member. The prominent highterrace outliers in the valley between Honcut Creek and the 

Yuba River are capped by the same coarse gravel deposit. 

At this time, we do not know whether this uppermost gravel 

bed is a pedimentlike veneer on an erosional surface, or 

whether it is merely the stratigraphically highest gravelly 

fan or flood plain deposit of the upper member of the 

Laguna Formation. Arkley (1962) and Marchand and Allwardt ( 1981) recognized that the Laguna Formation and 

younger alluvial deposits in the northeastern San Joaquin 

Valley coarsen upward and that gravel beds cap several of 

them, including the Laguna. These and other authors have 

variously interpreted the capping gravel as pedimentlike 

veneers or as the final stage of deposition of upwardcoarsening alluvial fan building. Cherven (1984) interpreted 

the capping gravel on the Laguna Formation as an upper fan 

facies (a facies deposited near the mountain front) of 

westward-prograding glacial outwash fans. He noted that 

the gravelly, upper fan facies of the Laguna Formation is 

found as a sheet deposit near the Sierra foothills and as 

linear ridges to the west that are either erosional remnants of 

the sheet deposit or preserved channel thalwegs. Although 

there are several possible correlative formations, for example the Red Bluff Formation, the Arroyo Seco Gravel, the 

China Hat Gravel Member of the Laguna Formation, and 

the North Merced Gravel, we refer to the gravel bed in this 

report as the uppermost gravel bed of the upper member of 

the Laguna Formation, because our information on the 

probable age and stratigraphic significance of the bed is not 

precise enough to suggest a definite correlation. 

A reference section in the upper member of the Laguna 

Formation that includes the uppermost gravel bed and part 

of the underlying dacite unit (the lower member is not 

represented at this exposure) is located south of Oroville 

and is described below: 

G26 Soil Chronosequences in the Western United States 

Reference section location: Site 2 of figures 2 and 5. Composite section 

includes roadcut in Ophir Road (north face), southeast sides/ope of the 

adjacent hill where we cut back the surface soil to expose sediments, the 

Western Pacific Railroad cut, and exposures in Baggett-Palermo Road, 

N£1/4 sec. 31, and SE1/4SE1/4 sec. 30, T. 19 N., R. 4 E., Palermo 

7.5-minute quadrangle. 

Top of the uppermost gravel bed in roadcut is at approximately 275 ft (85 

m) in elevation. The surface is somewhat stripped and only the hardpan 

(silica-cemented duripan of pedogenic origin) remains from what was 

probably a Redding series (Abruptic Durixeralfs) soil profile. The central 

part of the section is poorly exposed on the side hill and descriptions are 

brief and approximate. 

Approximate 

thickness (m) 

Laguna Formation: 

Upper Member: 

14. Coarse mixed gravel, channeled into underlying 

beds; subrounded to rounded gravel in a coarse 

reddish sand matrix; cobbles average 10 to 15 em in 

diameter but cobbles up to 40 em are common; 

bears remnants of a soil profile with a duripan; 

basal contact quite flat with less than I m of relief. 2-3 

13. Fine sandy sediment, thin-bedded; weathered buff 

to brown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 

12. Coarse sand, thin- to medium-bedded; fills a distinct channel cut into underlying sediments; neutral 

gray ih color; channel approximately 6-8 m wide .. 0-1.5 

11. Fine sand, as in bed 13; weathered buff............ -1 

10. Paleosol formed in fine silty sediments; strong 

brown to reddish-brown color; silty clay loam 

texture; fine and medium angular blocky structure; 

moderately thick patchy clay films coating peds; 

former argillic horizon with A horizon apparently 

removed by erosion; sharp upper contact, wavy, 

gradual lower boundary; paleosol appears to dip 

slightly to the west .................................... . 

9. Silty fine sand; thin- to medium-bedded; weathered 

brown ..................................................... 1.5 

8. Slightly gravelly sand; medium sand at base with a 

few fine, subrounded gravel clasts; grades upward 

to fine sand and silty fine sand; weathered brown to 

buff........................................................ 2 

7. Silt, with very fine sand; thinly bedded; weathered 

chocolate brown; tuffaceous appearance, fine white 

(1 mm) pumice(?) fragments; root casts and animal 

burrows(?); section poorly exposed on sideslope; 

cobbly lag gravel mantles lower hillslope and flat 

area near intersection of road . . . . . . . . . . . . . . . . . . . . . . . . . -3.5 

6. Silty fine sand and sand; thin to medium bedded; 

weathered gray to brown.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

5. Dense silt; thin bedded to very thin bedded; buff to 

gray; tuffaceous(?) ..................................... . 

4. Sand; medium to coarse; in trough crossbed sets 

with amplitudes approximately 2 m; interbedded 

tight-packed tuffaceous(?) silt is draped over crossbeds; sand may have a component of blue lithic 

volcanic fragments; thin lenses of fine gravel also 

interbedded; individual bodies of sand are lens 

shaped but the unit persists laterally; sand-size 

weathered dacite(?) in silts . . . . . . . . . . . . . . . . . . . . . . . . . . . . -3-4 

3. Mixed coarse gravel; massive; coarse sand matrix; 

with a few sand lenses; gravel subrounded . . . . . . . . . 4 

Unconformity. 

Dacite unit: 

2. Fine sand; tuffaceous; contains lithic fragments of 

dacite; weathered gray to buff . . . . . . . . . . . . . . . . . . . . . . . . 2 

1. Medium sand; tuffaceous; contains angular quartz, 

and euhedral hornblende and biotite, lithic fragments of dacite, and a few dacite pebbles; weathered medium gray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Total thickness ........................................ 29-31 
This sequence of beds in the upper member appears to 

have been deposited in a meandering-river environment 

much like that of the modem Feather River. From the 

foregoing description it would appear that unit 3 is a 

channel-lag gravel, units 4 through 6 are point bar deposits, 

and unit 7 is an overbank silt of vertical accretion. At the 

Highway 70 cut 1.5 km to the west, units 1 through 7 appear 

to be present, but above unit 7 is a thick gravel that may be 

the base of a new fill sequence. 

The thickness of the upper member varies. In the 

Thermalito Power Canal the upper member is represented 

solely by the uppermost gravel unit, with a single deeper 

channel beneath it at one point along the exposure. At this 

site, the upper member was deposited on an erosional 

surface cut into the underlying dacite unit. Here the total 

thickness varies from 9 to 15 m, and the basal elevation of 

the upper member is approximately 260 ft (80 m). Along 

the present Feather River 1.5 km south, gravel deposits 

belonging to the upper member are at least 30 m thick in a 

channel that was cut much deeper into underlying rocks 

than at the Thermalito Canal. In the subsurface due west of 

Oroville, along Highway 99, the section that we attribute to 

the upper member is approximately 23 m thick. The 

deposits on the Yuba were not as closely studied, but 

sediments of the upper member in the prominent terrace 

outliers are approximately 15 to 21 m thick. 

lower Member 

East of Oroville, the lower member of _the Laguna was 

deposited unconformably on surfaces eroded into Jurassic 

bedrock and into the dacite unit. The fan-shaped flood plain 

of the lower member of the Laguna issued from an apex 

centered near Sycamore Hill (NWI/4 sec. 3, T. 19 N., R. 3 

E., Oroville 7 .5-minute quadrangle) at an elevation of 

approximately 500 ft (150 m). The ancestral Feather River 

apparently flowed to the southwest or south, because 

south-trending remnants of the lower member cap the 

bedrock ridge that lies to the east of Oroville and Palermo 

and continue south to Honcut Creek (fig. 2). 

Along the ancestral Yuba River the lower member of 

the Laguna Formation was also deposited unconformably 

over the dacite unit and older rocks. Beds of gravel and sand 

that contain the Nomlaki Tuff Member overlie thin remnants of a dacitic mudflow and also overlie bedrock in a 

series of exposures along the Smartsville Road (SEI/4 sec. 3, 

T. 15 N., R. 5 E., Browns Valley 7.5-minute quadrangle). 

The ancestral Yuba River appears to have been flowing to 

the west at this time. 

The lower member consists of fluvially deposited 

gravel, sand, and silt of mixed lithology and mineralogy. 

The gravel contains several rock types including common 

clasts of blue silicic metamorphic rocks and white quartzite 

and several different types of metavolcanic rock, including 

a pale-greenish-white felsic metavolcanic(?) rock that is 

commonly very highly weathered. Metasedimentary rocks 

locally dominate metavolcanic rocks in the cobbles by 2 or 

3 to 1. Volcanic rocks-andesite, basaltic andesite, basalt, 

and dacite-make up less than 20 percent of the gravel. 

Tonalite or granodiorite usually makes up less than 5 

percent of the gravel. Gravel exposed near the base of the 

section contains as much as 20 percent dacite blocks, 

indicating that the dacite was reworked into basal sediment 

of the lower member of the Laguna at the contact (for 

example, an exposure 150 m west of the intersection of 

Foothill Boulevard and Olive Highway, SWI/4 sec. 16, T. 19 

N., R. 4 E., Palermo and Oroville 7 .5-minute quadrangles). 

Gravel higher in the section includes less than 1 percent 

dacite cobbles. 

Gravel and cobbles are subrounded or rounded and, 

east of Oroville, nearer the ancestral mountain front, they 

average 10 to 15 em in diameter. The largest are about 30 

em in diameter. Gravel of the lower member is fresh or 

highly weathered, with the more weathered gravel generally 

nearer the original upper surface of the deposit. Clasts of 

granite are weathered in place to grus, although the biotite 

in them appears unaltered. Metavolcanic and volcanic 

gravel can be quite weathered and commonly respond with 

a dull thud when struck. Clasts of siliceous metamorphic 

rocks are fresh. 

Sand of the lower member is dominated by quartz and 

feldspar, with a large component of lithic grains derived 

from all of the rock types also represented in the gravel. 

Sand tends to be coarse, subrounded, and like the gravel, 

highly weathered. Sand of the lower member can generally 

be crushed to a powder in the hand. The lower member of 

the Laguna is not well exposed. No reference section is 

designated, but some of the best exposures of the lower 

member can be seen at several sites in sees. 10, 15, and 16, 

T. 19 N., R. 4 E. Remnants of the lower member of the 

Laguna Formation east of Oroville and extending south 

toward Honcut Creek are dominated by coarse gravel to 

cobble conglomerate with a few lenticular sandy beds. 

These coarse conglomerate beds occur near the postulated 

apex of the fan-shaped flood plain at the mouth of the 

ancestral canyon. West of Oroville, in the subsurface at 

greater distance from the apex, the deposit consists of 17 m 

of basal fine gravel and fine gravelly sand overlain by 

stratified silt and silty clay (California Department of Water 

Resources drill record 79-107 A). 

As we have represented them, all of the conglomerate 

deposits at higher elevations in the eastern part of the 

project area are included in the lower member of the 

Laguna Formation. These include the deposits near the town 

of Bangor at elevations up to 960ft (290m). The conglomerate that trends west from Bangor appears to have occupied 

an ancestral channel of the North Fork of Honcut Creek. 

The composition of this gravel is mixed and includes 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G27 
metasedimentary, metavolcanic, volcanic, and gramttc 

rocks. Cobbles here are as much as 80 em in diameter and 

are well rounded but poorly sorted. The lithology is similar 

to other deposits of the lower member of the Laguna and 

unlike the older Tertiary auriferous gravels, which tend to 

be dominated by chert, quartzite, and(or) volcanic rocks. 

The channel fill appears to be as much as 80 m thick, 

although this may be an overestimate because the cobbles 

may be mantling erosional sideslopes. Although the deposit 

is deeply eroded, reconstruction of the original surface of 

the deposit shows it to be roughly continuous with the more 

extensive remnants of the lower member 3 to 5 km to the 

west. Because of similar cobble lithologies and the reconstructed surface extent, this deposit has been included with 

the lower member of the Laguna. It is conceivable that it 

represents deposition over an extended period from early 

Miocene(?) time to Laguna time. No definitive evidence is 

available on the age of these high gravels. 

The most extensive area of conglomerate in the lower 

member of the Laguna lies south and west of the town of 

Wyandotte at elevations averaging 500 to 600ft (150-180 

m). These exposures are generally bounded on the west and 

separated from the Sacramento Valley by a north-southtrending bedrock ridge, and bounded on the east by the 

canyons of North Honcut and Fine Gold Creeks. These 

exposures of conglomerate are grouped- with the lower 

member of the Laguna Formation for several reasons. First, 

the dissected topography is strikingly similar to that underlain by the lower member of the Laguna Formation east of 

Oroville that contains the Nomlaki Tuff Member. The 

deposits in question are in fact laterally continuous with the 

lower member east of Oroville. The elevations of both the 

basal contact and the reconstructed upper surface of the 

deposit are essentially the same as corresponding surfaces 

of the lower member of the Laguna. In addition, the highest 

hilltops of the deposit display the striking soil profile that 

we associate with relict surfaces of the lower member of the 

Laguna Formation. The deposits near Wyandotte may 

overlie remnants of older gravel deposits, and along North 

Honcut and Fine Gold creeks the gravel deposits may 

include younger fills of gravel inset into the main deposit. It 

is thus possible that the deposit may be more diverse in age 

and origin than we have shown in the correlation of map 

units (fig. 2). 

The thickness of the lower member of the Laguna can 

be estimated from topographic maps and drill logs. In the 

foothill area east of Oroville, the base of the lower member 

may be as low as 450ft (135m): an exposure on Oro-Dam 

Boulevard (200m north-northwest of the center sec. 10, T. 

19 N., R. 4 E., Oroville 7.5-minute quadrangle) contains 

basal gravel of the lower member in a channel cut into 

metamorphic bedrock. At other locations in the area, the 

basal contact is at elevations of 400 to 500ft (120 to 150m) 

and either gravel or the Nomlaki Tuff Member locally forms 

the basal part of the lower member. At the east comer SWI/4 

G28 Soil Chronosequences in the Western United States 

sec. 4, T. 19 N., R. 4 E. (Oroville 7.5-minute quadrangle) 

just off Long Bar Road, the Nomlaki Tuff Member lies 

directly on metamorphic bedrock at an elevation of 450 ft 

(135 m); on Meadowview Road (site 3 of figs. 2 and 5, 

NWI/4NEI/4 sec. 15, T. 19 N., R. 4 E., Oroville 7.5-minute 

quadrangle) the Nomlaki Tuff Member lies on a transition 

zone of reworked dacitic sediments above dacite lahars. The 

highest hilltops associated with the lower member are at an 

elevation of 600 ft (180 m). Thus, while the maximum 

thickness may be 60 m in the area east of Oroville, 45 m is 

probably the average thickness. Similar thicknesses occur to 

the south in the Wyandotte area. In the subsurface 13 km 

due west of Oroville, sediments that we interpret as within 

the lower member have a preserved thickness of 26 m. In 

contrast, only 15 to 18m of sediment of the lower member 

is preserved on Honcut Creek where it overlies dacitic 

sediments (possibly reworked). The lower member does 

appear to thicken substantially to the west. The thickness of 

the lower unit on the Yuba River is difficult to estimate, but 

from limited surface exposures, it appears to be 7 to 12 m 

in the vicinity of Beale Air Force Base where an unknown 

thickness has been removed by erosion. 

Nomlaki Tuff Member 

A widespread time-stratigraphic marker, the Nomlaki 

Tuff Member occurs at or near the base of the lower 

member of the Laguna Formation. Positive correlation was 

made by Andrei Sarna-Wojcicki (oral commun. 1980) of 

the U.S. Geological Survey from samples collected east of 

Oroville during fieldwork following the 1975 Oroville 

~arthquake. He also identified bedded ash collected in a 

roadcut along Smartsville Road south of the Yuba River as 

correlative with the Nomlaki Tuff Member (NEI/4 sec. 8, T. 

15 N., R. 5 E., Browns Valley 7.5-minute quadrangle). 

The Nomlaki Tuff Member exposed in the area is a 

fluvially derived, crystal vitric tuff interbedded with layers 

containing abundant, subrounded pumice pebbles that range 

in size from 0.5 to 5 em. The pumice pebbles are composed 

of vesicular, transparent to white glass that contains angular 

and euhedral quartz, feldspar, hornblende, and orthopyroxene(?). Individual tuff beds are thinly bedded (3 to 10 em) 

in alternating layers of tuffaceous sand, silt, and pumicepebble sand. The sand is flat bedded and crossbedded; silt is 

finely laminated. Beds of the tuff are neutral gray, chalky 

white, or pale tan in outcrop. 

Creely (1965, p. 64-66) included a very complete 

description of the Nomlaki Tuff Member from similar 

outcrops. Although he stated that the tuff was probably 

similar in source and age to the Nomlaki, he stopped short of 

making the direct correlation and called it instead the 

"unnamed rhyolitic pumice tuff," placing it at the same 

position as the Nomlaki Tuff Member in his stratigraphic 

correlation table. Creely measured the refractive index of 

glass from the Oroville exposures and obtained values of 
1.500 to 1.511 ±0.003, indicating a silica content of 67 to 

69 percent and a rhyodacitic composition (1965, p. 65). 

These values are very close to those of 1.500 to 

1.502±0.001 measured by Sarna-Wojcicki (1976, p. 13) on 

glass from the Nomlaki Tuff Member of the Tehama 

Formation. 

The Nomlaki appears to lie at or near the base of the 

lower member of the Laguna. At Meadowview Road (site 3 

of figs. 2 and 5, NWI/4NEI/4 sec. 15, T. 19 N., R. 4 E., 

Oroville 7 .5-minute quadrangle) at an elevation of 500 ft 

(150 m), the Nomlaki Tuff Member lies on dacitic sediments of the dacite unit with an apparent gradational 

contact. One kilometer to the north, at an elevation of 450 

ft ( 135 m), gravel of the lower member of the Laguna rests 

directly on metamorphic bedrock. The Nomlaki Tuff Member appears to be underlain locally by mixed gravel. The 

lithologic similarity between, and the stratigraphic association of, the Nomlaki Tuff Member and the dacite unit draws 

attention to the possibility that they are different phases of 

the same eruptive cycle. 

Post-Laguna, Pre-Riverbank Erosion 

The complex of erosional surfaces cut into the Laguna 

Formation near Oroville, and especially those cut into the 

upper member of the Laguna Formation, are important to 

the interpretation and regional correlation of deposits. 

These high terrace surfaces present a strikingly stepped 

appearance, particularly southwest of Oroville. It is difficult, however, to identify corresponding surfaces across the 

Feather River and to the south along the margin of the 

valley, because they generally have different slopes and 

elevations and are not as clearly expressed. For example, on 

the south side of the Feather River (sees. 29, 31, T. 19 N., 

R. 4 E., and sec. 36, T. 19 N., R. 3 E., Palermo 7 .5-minute 

quadrangle), the uppermost gravel bed of the upper member 

of the Laguna has a reconstructed slope of 9-11 m!km (fig. 

4A), based on aN. 20° W. strike, and a maximum elevation 

of 346ft (105m). Corresponding remnants, on strike to the 

north of the Feather River, have a slope of approximately 5 

m/km and rise to barely 300 ft (90 m) in elevation. The 

stepped appearance, particularly southwest of Oroville, led 

Lindgren ( 1911) and geologists from the Division of Mines 

and Geology (Sherburne and Hauge, 1975) to postulate that 

the high terrace surfaces represent as many as four separate 

inset alluvial fills (within our Laguna Formation). We found 

no evidence for multiple inset alluvial fills corresponding to 

these geomorphic surfaces. Our interpretation, as described 

here and below, involves tectonically related erosional 

dissection of the Laguna Formation in post-Laguna but 

pre-Riverbank time that exhumed the buried surface and the 

buried paleosol on the lower member of the Laguna. 

At least two major erosional surfaces were cut into the 

deposits of the Laguna Formation between deposition of the 

uppermost gravel bed of the upper member of the Laguna 

and the deposition of the Riverbank Formation (fig. 4A). 

These erosional features predate and do not include incision 

that immediately preceded deposition of the Riverbank 

Formation. The older of the two erosional events resulted in 

the shaping of the major surface of the Thermalito area west 

of Oroville. Remnants of the resulting surface are also 

visible as a 200-ft-elevation (60 m) surface on Highway 70 

southwest of Oroville (sees. 35 and 36, T. 19 N., R. 3 E. 

and sec. 1, T. 18 N., R. 3 E., Palermo 7.5-minute 

quadrangle). North of Oroville, the elevation of this surface 

is approximately 260 ft (80 m), and it decreases to the 

west-southwest with a slope of about 5 mlkm. The most 

widespread average elevation for this erosional surface in 

the Thermalito area is about 200ft (60 m). For example, the 

Oroville airport is on this surface. In part, the elevation of 

this surface is controlled by resistant units such as gravel 

beds within the Laguna. The surface, where cut in nongravelly sediments, appears to be strictly erosional; where cut in 

gravelly beds, such as the uppermost gravel bed, the 

erosional surface is mantled by a lag of gravel as much as 

several meters thick. This appears to be the case in sec. 36, 

T. 19 N., R. 3 E. where a large erosional surface at 

approximately 200ft (60 m) in elevation is mantled by a lag 

of gravel derived from the uppermost gravel bed. We 

cannot definitely associate any thicker, more continuous 

deposits with this erosional surface, although exposure is 

poor. 

The second and younger surface is prominent at an 

elevation of approximately 160 ft (50 m) between Oak 

Grove and Palermo (fig. 2), and as a series of outliers that 

crop out south to Honcut Creek. This erosional episode 

exhumed at ~east part of the lower member of the Laguna 

Formation and its buried soil, and consequently, the surface 

displays a soil profile that in places is much more strongly 

developed than soils on topographically higher surfaces. 

The soil profile that exists on this exhumed surface in ~he 

lower member of the Laguna may be the net result of two 

periods of soil formation, one before burial by the upper 

member and the other after exhumation. We have not found 

evidence of alluvial fills on this geomorphic surface that are 

equivalent in age to the erosional episode. 

Soil Landscapes 

The great age and complex erosional and depositional 

history of the Laguna Formation produced a large array of 

different soils on various parts of the formation. Few 

remnant surfaces exist on the uppermost gravel bed of the 

upper member of the Laguna, and no soil was sampled from 

this surface for the chronosequence study. The soils found 

on little-eroded parts of the uppermost gravel bed of the 

upper member are commonly quite strong representatives of 

the Redding series (Abruptic Durixeralfs) or those of the 

Red Bluff series (Ultic Palexeralfs). The Redding soils have 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G29 
yellowish-red (5YR 5/6D) very gravelly loam A horizons, 

and red (2.5YR 4/6D) gravelly clay Bt horizons at depths of 

0. 5 to 1 m that overlie reddish-brown or yellowish-red 

(5YR 4/4 or 5/6D) strongly cemented iron-silica duripans 1 

to 1. 5 m thick. Sediments beneath the soils are weathered 

and red gravelly clay loams to a depth of 4 to 5 m. A 

particularly complete example of the Redding soil on the 

uppermost gravel bed occurs on the south side of the 

Thermalito Canal 300 m east of Cherokee Bridge in the 

SWI/4 sec. 5, T. 19 N., R. 4 E. (Oroville 7.5-minute 

quadrangle). Most of the surfaces of the uppermost gravel 

bed have been stripped to the duripan of the Redding soil. 

A good example of this is displayed south of Oroville at the 

283-ft (85 m) hill in the NEI/4 sec. 31, T. 19 N., R. 4 E. 

(Palermo 7 .5-minute quadrangle). 

Multiple erosional surfaces descend from the highest 

remnants of the upper member of the Laguna Formation. 

Flat and rolling erosional surfaces cut at elevations below 

the uppermost gravel bed have Redding and Corning series 

(Typic Palexeralfs) soils. Extensive examples of this soil 

landscape surround the Oroville airport and the Thermalito 

Afterbay area. A well-developed mound and swale microrelief exists in areas of the Redding soils. Soils on steeper 

sideslopes in mixed materials of the upper member of the 

Laguna Formation have been mapped as the less strongly 

developed Cometa series (Typic Palexeralfs). The Agate 

variant (Typic Durochrepts) has also been mapped on steep 

sideslopes. Erosional sideslopes underlain by finer materials bear soils of the Altamont series (Typic Chromoxererts). 

In Yuba County, the Burris series (Chromic Pelloxererts) 

has been mapped on colluvial sideslopes and toeslopes of 

the Laguna Formation. 

Well-preserved, never-buried remnants of the soil originally formed on the lower member of the Laguna Formation are rare. We have informally named this soi1 the Red 

Bluff strong variant (Palexerults). Most commonly the 

profile of this soil has been partially eroded, but the 

near-total weathering of nonsiliceous clasts, lOR color 

hues, the presence of red and pinkish-gray to white reticulate mottling, and the great depth of soil formation serve to 

identify this soil. Over broad areas east of, Palermo and 

Oroville, erosional surfaces are cut deeply into the lower 

member of the Laguna Formation and brown, gravelly, 

Newville variant soils (Typic Haploxeralfs) have formed. 

These soils have formed in the colluvial mantle of the 

erosional sideslopes. On Lower Wyandotte Road in the 

SWI/4 sec. 35, T. 19 N., R. 4 E. (Bangor 7.5-minute 

quadrangle), a roadcut exposes a deeply eroded remnant of 

the Red Bluff strong variant soil. As much as 5 m of the 

upper profile has been removed by erosion at this site. The 

modem rolling hillslopes very obviously truncate this extreme soil profile, and the sideslopes are mantled by 

colluvium on which the Newville variant soil has formed. 

Exhumed remnants of the lower member of the Laguna 

bear a variety of soils. Most commonly, strong variants of 

GJO Soil Chronosequences in the Western United States 

the Redding series or of the Coming series cap the exhumed 

surfaces, and these older soils may be partially truncated by 

th~ present-day topography. Because of ongoing erosion, 

the older soils show a range in the thickness and completeness of the upper profile, but the lOR color hues, great 

depth_ of soil formation, and extreme weathering of cobbles 

are diagnostic. 

Less commonly, exhumed remnants of the lower member of the Laguna bear the complete Red Bluff strong 

variant soil profile that is very similar to the soil profile 

found on parts of the lower member of the Laguna that were 

never buried. These soils apparently underwent little erosion of their deep soil profile prior to burial by alluvium of 

the upper member of the Laguna Formation, and soil 

formation resumed after re-exposure in pre-Riverbank time. 

This is the case on Honcut Creek at the site sampled for the 

chronosequence study. Here the soils have reddish-brown 

(2.5YR 4/4D) loam A horizons over dark-red (lOR 3/6D), 

clay argillic (Bt) horizons that begin at about 0.4 to 0.6 m 

and extend to a depth of almost 3 m. Pale-white and 

dark-red reticulate mottling is conspicuous near the base of 

the Bt horizons and extends to more than 5 m in BCt 

horizons. Total depth of weathering of this ancient soil may 

exceed 10m. 

Geochronology and Correlation 

The paleomagnetic stratigraphy of the Laguna Formation and the dacite unit, and radiometric ages of the 

Nomlaki Tuff Member and dacite unit, allow us to correlate 

the Laguna Formation in this area with the Laguna Formation in its type location and to estimate the age of the 

formation. The most complete section sampled for magnetic 

polarity zonation extended through 30 m of sediments at the 

reference section described above for the upper member of 

the Laguna (site 2); 29 samples were collected at approximately 1-m intervals. In addition, the magnetic polarity of 

the Nomlaki Tuff Member was measured at two sites (sites 

3 and 4 of figs. 2 and 5). Six samples of the Nomlaki Tuff 

Member from two separate exposures yielded reverse polarities with strong magnetizations. The radiometric age of 

the Nomlaki, using the new decay constant, is 3.4 m.y. 

This age corresponds to the end of the Gilbert ReversedPolarity Chron. The paleomagnetic and radiometric ages are 

consistent. The Nomlaki appears to lie at or near the base of 

the lower member of the Laguna Formation. The base of the 

lower member, therefore, is less than 3.4 Ma, but the age of 

the upper part is not known directly. 

Radiometric dating of the blocks of dacite within a 

lahar in the dacite unit gave ages that range from 2.8 to 3.4 

Ma (supp. table 9). The dacite unit underlies the Nomlaki, 

therefore these dates and the age of the Nomlaki Tuff 

Member are reversed compared to their stratigraphic sequence. The analytical uncertainty associated with the dates 
1-

z 

:::> 

z 

0 

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~ 

a: 

0 

LL 

< z 

:::> 

(!) 

::s 

w 

1-

u 

< c 

1-

z 

:::> 

CD 

:::> 

en 

u;-o 

0 Q) E.o 

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.= 

----.----------

METERS 

t: 

SITE 1 

Covered 

<\) 0 ·-~0. 

d ·a· O~c:;) 

o<::J ~ 

~~~ ~ 

MAGNETIC POLARITY 

----"' ---r--._ 

----?. ·----

EXPLANATION 

~ Gravel and cobbles, sandy matrix 

ffi Poorly developed buried soil 

j:.:·:_.:a·;: ~J Sand, in part cross bedded 

~ Silt and silty fine sand 

"0 

<U ~ E Q) .... > 0 Q) 

za: 

--

~~ "fO-~ Volcanic mudflow with angular blocks of dacite 

~~'[)·~-~ Slightly gravelly sand 

z 

0~ a:< 

:I:~ 

uo 

coz 

~< 

------!?- Correlation between sections and magnetic polarity 

scale-Dashed where approximate; queried . 

where uncertain 

Contacts 

Conformable 

..__._._, Unconformable 

ns z ~ 0 

a: w 

:I: ~ () i= 

1.0 

Figure 5. Correlation of samples with an established magnetic polarity time scale (Mankinen and Dalrymple, 1979) for 

site 1, Feather River; site 2, Western Pacific Railroad; site 3, Meadowview Road; site 4, Wyandotte Road. Normal (N) and 

reverse (R) magnetic polarity of samples is shown on right side of sections. See figure 2 for locations; see text for 

interpretation. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G31 
for the two units overlap, however, so . the ages are 

statistically indistinguishable. 

The magnetic polarity of the upper member of the 

Laguna at the reference location is normal in the lower 

two-thirds of the section (units 3 through 8 of the description) to a point 2m below the buried paleosol, and reversed 

from there to the base of the uppermost gravel bed (fig. 5). 

A coarse channel fill within the reversed zone (unit 12) has 

a questionable normal polarity, possibly indicating a brief 

polarity event. A single sample from a sand lens within the 

uppermost gravel bed also yields a questionable normal 

polarity. We know that this section is younger than the 

lower member of the Laguna, which in turn is younger than 

3.4 Ma. The strength of development of the soil formed on 

the lower member of the Laguna where buried by the upper 

member, or where exhumed, argues for a long period of 

time between deposition of the two members. Even with the 

effect of a wetter Pliocene climate the time must have been 

0. 5 million years or more. 

Based on these considerations, we associate the 

normal-to-reversed transition in the upper member with the 

normal-to-reversed boundary between the Gauss NormalPolarity and Matuyama Reversed-Polarity Chrons. This 

boundary is presently dated at 2.48 Ma (Mankinen and 

Dalrymple, 1979). If this correlation is correct, then the 

normally polarized channel fill in the upper reversed zone 

might represent the Reunion Normal-Polarity Subchron or 

"X" polarity event at about 2 to 2.1 Ma. Furthermore, if 

the uppermost gravel bed of the upper member of the 

Laguna is normally magnetized, as is suggested by our 

single measurement, it may have been deposited during the 

Olduvai Normal-Polarity Subchron or possibly during the 

Jaramillo Normal-Polarity Subchron presently dated at 

about 1.75 and 0.9 Ma, respectively. 

Harwood and others ( 1981) reported bracketing ages of 

0.45 and 1.1 Ma for a gravel deposit along the front of the 

Chico monocline that they correlated with the Red Bluff 

Formation. Helley and Harwood (1985), in a regional map 

of Tertiary and Quaternary deposits, correlated the uppermost gravel bed of the upper member of the Laguna in the 

Feather River area with the Red Bluff Formation. This correlation, and an age of 0.45 to 1.1 Ma for the uppermost 

gravel bed of the Laguna, is not precluded by the evidence 

we present. We favor instead the Interpretation that the 

uppermost gravel bed was deposited during the Olduvai and 

thus has an age of about 1.75 Ma, because 1.4 million years 

or more (2.48 minus 1.1) seems an excessive period of time 

to deposit the upper few meters of the upper member of the 

Laguna Formation. 

We correlate the two alluvial members of the Laguna 

Formation in the Feather-Yuba Rivers area with the two 

members of the Laguna that were recognized by Marchand 

and Allwardt (1981) in the San Joaquin Valley. Our 

correlation is provisional but is based on similarities in 

geomorphic expression, radiometric ages, and magnetic 

polarity zonation in the units in the two areas: Marchand 

G32 Soil Chronosequences in the Western United States 

and Allwardt (1981) recognized an unconformable contact 

separating two units of the Laguna in the Merced River area 

by the presence of a strongly developed buried soil on the 

surface of the older unit. The deposits of the Laguna 

Formation are the oldest nonvolcanic alluvial units in both 

areas; they present the most highly elevated and dissected 

remnants of mixed alluvium in both areas. In the Kings 

River area of the southern San Joaquin Valley, gravel 

deposits correlated with the Laguna by Marchand and 

Allwardt (1981) contain clasts of a basalt with a K-Ar age 

of 3.76±0.08 Ma. Marchand and Allwardt (1981) also 

reported, from preliminary paleomagnetic studies of the 

Laguna, that the lower unit is magnetically reversed and the 

upper unit is normal, and they suggested that the boundary 

between the two might correlate with the Gilbert-Gauss 

boundary at 3.4 Ma (Mankinen and Dalrymple, 1979). 

A preliminary study of paleomagnetic zonation in the 

Laguna Formation in a series of roadcuts near Sloughouse 

in Sacramento County showed that the upper part of the 

section had reverse polarity, while the thicker, lower part 

displayed normal polarity (R.J. Shlemon, oral commun., 

1981). This suggests that the reference section of the upper 

member at Oroville and the section in Sacramento County 

are correlative, but such a correlation does not place direct 

time limits on the units. 

Our best estimate of the ages of the Laguna Formation 

at Oroville, based on tephrochronology, paleomagnetic 

stratigraphy, and soil development, are: deposition of the 

lower member of the Laguna from about 3 .4(?) to 3. 2 Ma; 

deposition of the upper member, possibly beginning about 

2.6 Ma and concluding with deposition of the uppermost 

gravel bed about 1.7 Ma or possibly 0.9 Ma. 

The Laguna Formation as described near the Feather 

River thus is broadly coeval with the Tehama Formation 

(Russell, 1931) and possibly the Red Bluff Formation, both 

of which occur extensively along the west side of the 

Sacramento Valley. The Tehama, as the Laguna described 

here, contains the Nomlaki Tuff Member near its base, but 

the age of the upper part of the Tehama is not known. No 

major hiatus is recognized within the Tehama. The similarity of time of inception of these major alluvial deposits 

(Tehama and Laguna) suggests a synchronous regional 

control on deposition, probably either climatic or tectonic. 

We favor the concept of tectonic control of the initiation of 

the major alluviation in the Sacramento Valley. 

In our interpretation, the geomorphic surfaces below 

the uppermost gravel bed of the upper member of the 

Laguna are primarily erosional, not depositional features. 

These surfaces may be coeval with the Arroyo Seco Gravel 

and "gravels of uncertain age" (Gale and others, 1939) in 

the American-Mokelumne Rivers area. Gale described the 

Arroyo Seco as a series of erosional surfaces cut into the 

Laguna Formation and veneered with pedimentlike gravel. 

Shlemon (1967a; b; 1972) disagreed with Gale's interpretation of the Arroyo Seco and stated instead that the Arroyo 

Seco surfaces in the American River area are actually a 
flight of terraces underlain by distinct alluvial deposits 

younger than, and cut into, the Laguna Formation. The 

most recent mapping of Quaternary deposits in the American River area, by Helley (1979), follows Gale's interpretation once again, and the Arroyo Seco is shown as one or 

more erosional surfaces cut into the Laguna Formation. 

One of the two erosional surfaces that we recognize 

here might also be coeval with the Red Bluff Formation, 

which has been extended into the Chico area by Harwood 

and others (1981), and which is now bracketed by radiometric ages of 0.45 and 1.1 Ma. 5 The erosional surface(s) 

may also be coeval with the North Merced Gravel recognized in the northeastern San Joaquin Valley (Marchand and 

Allwardt, 1981). 

The Turlock Lake Formation and the Fair Oaks Formation (partially equivalent) (Marchand and Allwardt, 

1981; Shlemon, 1967a, b) are major deposits of middle 

Pleistocene age in the northeastern San Joaquin Valley that 

lie in the stratigraphic interval between the Laguna and 

Riverbank formations. We have not recognized any extensive depositional units equivalent to the Turlock Lake or 

Fair Oaks Formations in the Feather-Yuba Rivers area. 

Dacite Unit 

A sequence of dacitic lahars interstratified with related 

volcaniclastic sediments underlie the alluvial terrace deposits throughout much of the project area. Although this unit 

is distinctive and widespread in the project area, it has not 

been recognized north of Oroville near Table Mountain, nor 

south of the Bear River (the next drainage south of the Yuba 

River). The unit is generally poorly exposed; it crops out in 

a few places in the foothills east and northeast of Oroville 

and in exposures near channel level on the Feather River, 

Wyandotte Creek, Honcut Creek, and the Yuba River. It 

has been penetrated by many research and test wells drilled 

by the California Department of Water Resources in the 

Oroville area, and it also appears in artificial exposures such 

as the Thermalito Power Canal. 

The dacite unit has been recognized by earlier workers, 

albeit with different extents and interpretations. Lindgren's 

( 1911) "Tuffs of Oroville" appear to have included the 

dacite unit and a part of the alluvial sediments that we 

correlate with the Laguna Formation. Creely (1965) 

grouped andesitic mudflows and conglomerates that lie 

beneath the Lovejoy Basalt with the dacite unit, and he 

provisionally correlated all of these with the Miocene and 

Pliocene Mehrten Formation (he used the term Mehrten(?) 

Formation). Dalrymple (1964) reported a K-Ar age of 23.8 

Ma from a tuff bed within the andesitic conglomerates 

beneath the Lovejoy Basalt, and this age has been assumed 

' In Helley and Harwood ( 1985), the uppermost gravel bed of the upper 

member of the Laguna, as described here, was correlated with the Red 

Bluff Formation. This is not precluded by the evidence we present, but our 

interpretation differs from that of Helley. 

by more recent workers to apply to the dacite unit as well 

as the andesites. Excavation of the Thermalito Power Canal 

north.ofOroville in the 1960's exposed a thick section in the 

dacite unit. Geologists from the California Department of 

Water ·Resources referred to these rocks as ''unnamed 

Upper Pliocene(?) volcanic sediments'' in early reports 

(California Department of Water Resources, 1968), but in 

late_r reports they adopted Creely's correlation of the dacite 

unit as part of the Mehrten(?) Formation. 

Evidence gathered by Busacca (1982) and summarized 

here demonstrates that the dacite unit is not related to the 

andesitic Mehrten(?) Formation of Creely, which indeed 

lies beneath the Lovejoy Basalt, but that instead it is a 

separate, younger volcaniclastic deposit. The reinterpretation is based on topographic, stratigraphic, lithologic, and 

radiometric evidence. The term dacite has been applied to 

these rocks based on elemental composition and mineralogy. Two blocks of the dacite have whole-rock compositions of about 60 percent Si02 , 16.5 percent Al20 3 , 3 

percent each Na20 and MgO, 1.5 percent K20, 5.5 percent 

CaO, and 6 percent total Fe as Fe20 3 . Plagioclase, hornblende, and biotite are the dominant minerals seen in hand 

specimen and thin section. Quartz and pyroxene are not in 

the rock. 

The dacite unit crops out at elevations of 300 to 500 ft 

(90 to 150 m) in the hills east and northeast of Oroville. 

This contrasts strongly with the Mehrten(?) Formation 

under the Lovejoy Basalt (Oroville Table Mountain), which 

crops out at elevations <:>f 850 to 950 ft (260 to 290 m) 

projected along a strike of N. 20° W. (regional tilt axis). 

Similarly, exposures of the dacite in the Thermal ito Power 

Canal are at elevations of 225 to 300ft (70 to 90 m), while 

2.5 krn to the north along the regional strike the Mehrten(?) 

Formation crops out under Table Mountain at 600 to 650 ft 

(180 to 200m). If the dacite unit and Mehrten(?) Formation 

are part of the same deposit, two parallel paleovalleys 

would have had to exist less than 3 to 5 km apart, but with 

350 to 500 ft (110 to 150 m) of elevation difference at 

comparable points along their length. This situation is not 

impossible in itself; what is improbable is that, subsequent 

to deposition of the dacite and valley filling, the higher 

valley then filled with lavas of the Lovejoy Basalt while the 

lower valley did not. 

The slope of the Mehrten(?) Formation and that of the 

dacite unit are markedly different. The base of the Mehrten(?) Formation beneath South Table Mountain has a 

slope of 29 to 33 m/km; that of the lahar unit of the dacite 

unit averages 4.6 to 17 m/km. While these slopes probably 

have been affected by local tectonics, the dominant effect is 

the regional tilting of the Sierra, and the difference indicates 

a significant difference in age between the two. 

Although the Mehrten(?) Formation under South Table 

Mountain is at a higher elevation than the dacite unit, it has 

a much greater slope. At about the position of the Campbell 

Hills (fig. 1), the tops of the two units are at nearly equal 

elevations. Farther to the southwest, in the subsurface, the 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G33 
tops of the two units converge and then cross over in 

relative elevation. 

We studied contact and stratigraphic relations of the 

dacite to underlying and overlying units in the Thermalito 

Power Canal and at other outcrops in the project area. In the 

Thermalito Power Canal, the dacite unit unconformably 

overlies gravel that is dominated by clasts of Lovejoy 

Basalt. This is the only known location where the base of 

the dacitic section is exposed. The basal contact is relatively 

smooth over the length of the 600-m exposure. The upper 

contact of the dacite unit is unconformable with overlying 

sand and gravel of the Laguna Formation. At the east end of 

the Thermalito Canal a channel-fill deposit of mixed gravel 

of the Laguna Formation is cut almost 9 m into dacitic 

sediments. At other locations, such as at Meadowview 

Road east of Oroville (site 3 of figs. 2 and 5, NWI/4NEI/4 

sec. 15, T. 19 N., R. 4 E., Oroville 7.5-minute quadrangle), the dacitic section is not well exposed but appears to 

grade upward into the Nomlaki Tuff Member of the Laguna 

Formation. At Honcut Creek there is also a mixed transition 

zone at the contact. There, about 2m of dacitic sand and silt 

lies on metavolcanic bedrock in the creek bottom (Nl/z sec. 

23, T. 17 N., R. 4 E., Lorna Rica 7.5-minute quadrangle). 

These deposits are overlain by a westward-thickening section of gravel and sand of the lower member of the Laguna 

Formation that contains an upward-decreasing percentage 

of dacitic pebbles and sand. 

On the Yuba River, fine dacitic silt and sand is 

unconformably overlain by coarse gravel of the Laguna 

Formation. The contact is sharp, with less than 0.5 m of 

reworked material between units. 

The dacite unit is very distinctive and recognizable in 

most exposures because it contrasts strongly with overlying 

mixed alluvial sediments. The laharic beds within this unit 

are light gray to medium brownish gray, massive, and 

compact or cemented. The matrix is poorly sorted, silty and 

clayey, and it contains abundant sand-size crystal, lithic, 

and possibly vitric fragments. Plagioclase, hornblende, and 

biotite are the dominant materials in the matrix. Sand- and 

fine-gravel-size lithic fragments derived from the dacite are 

ubiquitous. Blocks of subangular, blue-gray dacite that 

average 10 to 15 em in diameter are set in the tuffaceous 

matrix of the lahar. Some outcrops of the lahar contain 

blocks as large as 60 em; other outcrops, such as at the 

Feather River, are dominated by dacite pebbles 3 to 6 em in 

size. 

The most common of several textural variants of the 

dacite blocks in the lahars is a fine- to medium-grained, 

equigranular rock with euhedral biotite, subhedral hornblende, zoned plagioclase, and a small amount of glassy 

matrix. Other variants observed included one with elongated hornblende laths (to 2 em), one with a frothy, 

vesicular, pumiceous matrix, and one with equant plagioclase crowded in a slightly glassy matrix. The most distinct 

feature of both the blocks of dacite and of sand-size lithic 

fragments in the matrix is their chalky white appearance 

when weathered. 

G34 Soil Chronosequences in the Western United States 

The two stratigraphic sections of the dacite unit with 

the best exposure are described below. The second one 

displays a basal contact with underlying units. 

Reference section location: Site 3 of figures 2 and 5. Meadowview Road 

exposure, begins at the intersection of Meadowview and Oro-Quincy 

Roads and extends eastward on Meadowview Road; NWI/4NEI/4 sec. 15, T. 

19N., R. 4 E., Oroville 7.5-minute quadrangle. 

The Nomlaki Tuff Member extends at least 3 m above roadway level at the 

intersection. Gravel of the lower member of the Laguna Formation overlies 

the Nomlaki Tuff Member and extends to the hilltop at 551 ft (168 m). 

Elevation of the intersection approximately 510ft (155 m). 

Approximate 

thickness (m) 

Laguna Formation: 

Nornlaki Tuff Member: 

4. Tuffaceous sand and silt; weathered neutral gray to 

buff; upper part more sandy; flat bedded to crossbedded, with lenses of rounded rhyolitic pumice 

pebbles to 2 to 3 em in diameter; lower part fine 

tuffaceous sand and silt; sediments are a mixture of 

vitric and crystal fragments; water laid; grades 

downward into silt derived from the dacite, contact 

not apparent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 5-6 

Unconformity, or possible gradational contact. 

Dacite Unit: 

3. Mixed, tuffaceous sand and silt derived from 

dacite, weathered tan to gray; finely bedded at top; 

becomes coarser and more obviously derived from 

the dacite toward the base; coarser sand is a mixture 

of lithic, crystal, and vitric (?) fragments; section 

partially covered; abrupt contact with mudflows 

below...................................................... 4 

2. Dacite mudflow(s); unsorted, matrix-supported 

blocks of subangular dacite set in a matrix derived 

almost exclusively from dacitic material; sand and 

fine· gravel-size lithic and crystal fragments dominate in the matrix; hard or indurated; gray to tan in 

color; 80-95 percent of the blocks are one of two or 

three slight textural variants of the dacite; blocks 

range in size from a few em to more than 50 em; 

dacite blocks bear euhedral hornblende and biotite. 5-7 

1. Mixed, flat-bedded and crossbedded tuffaceous 

sand and silty sand; gray to tan; apparently derived 

from dacitic material; poorly exposed, base not 

exposed.................................................... 2-4 

Total Thickness ....................................... 16-21 

Reference section location: Thermalito Power Canal exposure; south face 

of the canal, east side of the Cherokee bridge; SW114 sec. 5, T. 19 N., R. 

4 E., Oroville 7.5-minute quadrangle. 

Top of bluff is approximately 305 ft (91 m). 

Approximate 

thickness (m) 

Laguna Formation: 

Upper member: 

Uppermost gravel bed: 

Unconformity. 

Dacite unit: 

4. Coarse, mixed, subrounded to rounded 

gravel in medium sand matrix; thick, red, 

Redding- series soil profile extends well into 

the gravel; basal contact is quite flat, but 600 

m to the east a 10-m-thick channel fill of 

mixed sand and gravel is interposed between 

this unit and the underlying dacite unit .. .. . -3 

3. Coarse cobbly sediments composed of dacitic 

gravel; apparently fluvial but exposure is poor and 

slope has been disturbed; 80-95 percent of cobbles 

are composed of dacite; other volcanic rocks and 

siliceous metamorphic rocks compose 5-20 percent; some cobbles are of very frothy, pumiceous 
Approximate 

thickness (m) 

Dacite unit-Continued 

variant of the dacite rarely seen elsewhere; weathers to a neutral gray; dips 1 o west.................... 10 

2. Top of this unit appears to be capped by a darkbrown soil profile; strongly weathered sediments 

are silt, clay, and sand exhibiting a variety of colors 

including gray, brown, yellowish brown, and tan; 

sand- and fine-gravel-size lithic fragments derived 

from the dacite throughout; a second, brown soil 

profile (?) occurs near the base . . . . . . . . . . . . . . . . . . . . . . . 10 

Unconformity. 

New Era(?) Formation of Creely ( 1965): 

I . Coarse gravel in a channel scoured into the underlying hard bedrock; clasts are subangular to subrounded, 10-20 em in diameter, and composed 

almost wholly of basalt derived from the Lovejoy 

Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Total thickness......................................... 31 

Paved below this point. 

Along Long Bar Road, just ~ortheast of downtown 

Oroville (SEI/4NWI/4 sec. 9, T. 19 N., R. 4 E., Oroville 

7 .5-minute quadrangle), sand and silt derived from the 

dacite is overlain by a thick lahar, which is overlain in turn 

by a thin section of dacitic sediments. On Linda Avenue 

500 m to the east, 4 m of the mudflow unit is exposed, 

capped by gravel assigned to the Laguna Formation. Directly under the mudflow is a possible soil profile formed in 

dacitic silt. This soil profile may correlate with the upper 

soil in a similar stratigraphic position in the Thermalito 

Canal. Along the Feather River due east of Thermalito, 

laminated silt is overlain by a thin (2 m) mudflow(?) with 

small dacitic pebbles, which in turn is overlain by bedded 

gray dacitic sand. Exposures on Honcut Creek and the Yuba 

River are generally of bedded, dacitic sand and silt. On the 

Smartsville Road, south of the Yuba River, a thin (2 m) 

dacitic mudflow crops out (SEI/4 sec. 3, T. 15 N., R. 5 E., 

Browns Valley 7.5-minute quadrangle). The dacite unit 

described here is thickest in the Feather or ancestral Feather 

River basin, is thinner to the south, and has not been 

recognized to the north of the Feather River. Honcut Creek, 

a small drainage of the middle foothill elevations, has only 

several meters of dacitic sediment. The undetermined 

source area appears to have been in the upper Feather River 

basin bordering the basins of the ancestral Yuba and 

possibly American Rivers. The stratigraphic evidence already discussed, the physical continuity with the Nomlaki 

Tuff Member in at least one exposure (the only exposure in 

the project area where the base of the Nomlaki is exposed), 

and gross compositional similarity between the dacite unit 

and the Nomlaki Tuff Member suggest that the dacite unit 

may represent an early eruptive phase of the Nomlaki. This 

hypothesis is supported by our radiometric dating and 

paleomagnetic stratigraphy. Whether the dacite and the 

Nomlaki Tuff Member were deposited in a single, continuous event or whether they were separated by a significant 

hiatus is not known. 

The maximum exposed thickness of the dacite unit in 

the mapped area is 21 m in the Thermalito Power Canal. To 

the west, drill-hole records show a minimum thickness of 

31 min the subsurface adjacent to State Highway 99 (drill 

record 79-107A), but there may be a problem here with the 

convergence in the subsurface of the dacite unit with 

Creely's Mehrten(?) Formation. 

Geochronology and Correlation 

The age of the dacite unit can be established from 

stratigraphic and radiometric evidence. It is younger than 

the Miocene Lovejoy Basalt, because gravel derived from 

the Lovejoy underlies the dacite. On Meadowview Road, 

the dacitic section is overlain directly by the 3.4 Ma 

Nomlaki Tuff Member. The base of the Lovejoy Basalt on 

South Table Mountain is at 900 to· 1 ,000 ft (270 to 300 m) 

while the base of the dacitic unit along the regional strike 2 

km to the south is 225 to 300ft (70 to 90 m). This implies 

a long period of erosion and canyon cutting after eruption of 

the basalt. By a similar argument the dacite unit could be 

latest Miocene or Pliocene in age because less than 10m of 

erosional relief was cut into the dacite prior to the deposition of the 3.4 Ma Nomlaki Tuff Member of the Laguna 

Formation. 

The paleomagnetic signature of fine dacitic sediments 

was sampled at three locations (sites 1, 2, and 3 of figs. 2 

and 5). The results are of questionable magnetostratigraphic 

value, because only partial sections were sampled and 

correlation of strata between sites is speculative. 

Four samples, two collected above and two below the 

fine gravelly dacitic lahar(?) at the Feather River site, have 

normal magnetic polarity. Other sites had at least one 

sample with reversed polarity, generally at the highest point 

sampled in the dacite section (in strata just below the 

contact with the overlying Laguna Formation). At least two 

buried soils were observed within the dacitic section·. The 

presence of buried soils and the existence of both normal 

and reversed polarities can be taken as evidence that 

deposition of the dacitic sequence took place over an 

extended period of time, possibly several tens of thousands 

of years. There also may be more than one silt-lahar-silt 

sequence in the section. 

Three dacite blocks from lahars at two locations were 

dated by K-Ar radiometric methods (supp. table 9). Duplicate whole-rock age determinations on one sample yield an 

average age of 3.2±0.1 Ma. Ages derived from hornblende 

and biotite mineral separates range from 2.8 to 3.4 Ma. 

Although these are minimum ages, the close stratigraphic 

association of the dacite unit with the Nomlaki Tuff 

Member makes it unlikely that these ages are in error by 

more than 50 percent. Creely (1965) correlated this dacite 

unit with the andesitic Mehrten(?) Formation that underlies 

the Lovejoy Basalt at Table Mountain. We have shown 

from stratigraphic, lithologic, and now radiometric evidence that these two units are not correlative. Dalrymple 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G35 
( 1964) dated a tuff bed within the andesitic conglomerate at 

Table Mountain (Mehrten(?) Formation) at 23.8 Ma. The 

revised stratigraphic association of the dacite unit reported 

above and the new radiometric ages support a middle 

Pliocene rather than an early Miocene age for this unit, and 

provides a very different and much younger bracketing age 

for inception of alluviation in the Feather River area. 

Pre-Dacite Cenozoic Units 

A series of Eocene to Miocene(?) sedimentary and 

volcanic units have been described by earlier workers in 

close proximity to the project area. To the north, in 

stratigraphic superposition are the Eocene lone Formation, 

overlain by the Miocene Mehrten(?) Formation of Creely 

( 1965)~ and by the Miocene Lovejoy Basalt that forms the 

prominent Table Mountain near Oroville. South of the Yuba 

River the pre-dacite Cenozoic units include the Oligocene(?) Reeds Creek Andesite and the Wheatland Formation of Clark and Anderson (1938). 

No unequivocal exposures of the lone Formation or 

Tertiary auriferous gravel were recognized in the project 

area, but several outcrops may represent small remnants of 

the lone Formation preserved beneath younger Cenozoic 

cover. 

Geologists from the California Department of Water 

Resources (1968) mapped a sequence of units within the 

Thermal ito Power Canal exposure: the informal ''Tertiary 

Greenstone Gravel,'' in channels cut into the bedrock, 

overlain by variegated clay and sand of the lone Formation, 

in tum overlain by ''unnamed Upper Pliocene(?) volcanic 

sediments" and capped by the "Red Bluff" Formation.· 

We have reinterpreted this exposure, in part on the 

basis of composition of their "Greenstone Gravel." The 

gravel is not greenstone, but is derived exclusively from the 

Lovejoy Basalt. In hand specimen and thin section the 

cobbles are indistinguishable from samples of the Lovejoy 

collected on nearby (but 300 m topographically higher) 

South Table Mountain. In thin section, the cobbles are 

black, microcrystalline olivine basalt containing scattered 

calcite-filled vesicles. A cobble of basalt collected from the 

deposit has 48.5 percent Si02 , 14.5 percent Al20 3 , 8 

percent CaO, and 12.2 percent Fe20 3 . A fresh sample of 

Lovejoy Basalt collected on South Table Mountain has 48.5 

percent Si02 , 14.5 percent Al20 3 , 7.7 percent CaO, and 

13.5 percent Fe20 3 . The gravel deposit, composed of 

cobbles of Lovejoy Basalt, may be correlative with the New 

Era Formation of Creely (1965). 

On this basis, the varicolored tan to yellow sand and 

clay that lies above the gravel, which was earlier correlated 

with the lone Formation (California Department of Water 

Resources, 1968), cannot be that, because the lone at Table 

Mountain lies stratigraphically below the Lovejoy Basalt. 

The variegated sediments are highly weathered and are 

derived from volcanic material. Exposure is poor, but these 

G36 Soil Chronosequences in the Western United States 

Table 4. Comparison of stratigraphic interpretations of an 

exposure in the Thermalito Power Canal (south side) at 

Cherokee Bridge (SW1f4 sec. 5, T. 19 N., R. 4 E.) 

Approximate Approximate California 

elevation thickness Department of This report 

of top Water Resources 

(1968) 

305ft 10ft Red Bluff Laguna Formation 

(3m) Formation 

295ft 35ft Unnamed Fresh dacitic lahars 

(10m) volcanic and conglomerates 

sediments 

260ft 35ft lone Highly weathered 

(10m) Formation dacitic sediments 

with several buried 

soils 

225ft 0-30 ft Greenstone Cobble conglomerate 

(0-9 m) Gravel derived from 

Lovejoy Basalt 

lone Formation 

(present locally 

in deep channels 

cut in bedrock) 

202ft Bedrock Bedrock series 

series 

Bottom of 

canal, 197 ft 

sediments co~tain sand- and small gravel-size fragments of 

chalky, white, weathered dacite. We correlate these varicolored sediments with the overlying dacite unit. A comparison of old and new stratigraphic assignments is given in 

table 4. The presence of at least two buried soils in this 

lower section of the dacite suggests that deposition was 

intermittent over an extended period of time. 

The relationships laterally along the base of the canal 

(now underwater) cannot be reexamined, but it is likely that 

some of the sediments that fill the deepest channels cut in 

bedrock and that were mapped as lone are, in fact, the lone 

Formation and underlie the Lovejoy Basalt gravel unit (New 

Era Formation?). This is indirectly suggested by the configuration of the lone, and of the Greenstone Gravel as 

shown in geologic section maps of the Thermal ito Canal cut 

(California Department of Water Resources, 1968). 

Strong postburial alteration by ground water may be responsible for the varicolored staining of both the deep part 

of the dacite unit and the lone Formation. 

The evidence presented here leads to a reassessment of 

the section exposed in the Thermalito Power Canal. Sedimentary rocks formerly designated as Eocene in age are 

here reassigned to the Pliocene based on their relationship to 

the gravel derived from the Lovejoy Basalt. 
Deformation and Tectonism 

The foothills and valley margin in the Oroville area 

were considered until recently to be seismically inactive, 

and although historic earthquakes have occurred in the 

surrounding region, the seismic hazards were considered 

minimal (California Department of Water Resources, 

1979). Part of the Foothills fault system (Clark, 1960) does 

strike north-northwest into the area, and this includes a wide 

shear zone in metamorphic bedrock in the Yuba RiverBrowns Valley area. Mesozoic faults that separate contrasting bedrock units were recognized by Creely (1965) and 

confirmed in studies by the Department of Water Resources 

(1979). Creely concluded that the Cenozoic rocks were 

essentially undeformed (1965, p. 79), but he did note that a 

fault to the east of Oroville had offset deposits of what he 

called the Red Bluff Formation about 2 m down to the west. 

Major late Cenozoic deformation of the Sacramento 

Valley has recently been documented (Harwood, 1984; 

Harwood and Helley, 1987). Near the project area, the 

Pliocene Tuscan Formation is complexly faulted and folded 

down to the west along the Chico monocline (Harwood and 

others, 1981; Harwood and Helley, 1987). The monocline 

extends for more than 75 km from Red Bluff to Chico. 

Harwood and Helley ( 1987) demonstrated that the monocline formed in response to movement on a deep-seated, 

east-dipping, high-angle reverse fault that bounds the east 

edge of the oceanic basement rocks underneath the Great 

Valley. 

The Oroville earthquake of August 1, 1975, Richter 

magnitude 5. 7, forced a rapid re-evaluation of the potential 

for seismic activity in the Oroville area. In studies by the 

California Division of Mines and Geology (Sherburne and 

Hauge, 1975) and the California Department of Water 

Resources (1979), geologists reported that the earthquake 

and ground rupture occurred along a previously unknown 

fault, which was named the Cleveland Hill fault. The 

Cleveland Hill fault is an en echelon segment of the longer 

Swain Ravine lineament fault zone. The Prairie Creek 

lineament fault zone runs at a slight angle to, and 3 to 6 km 

west of, the Swain Ravine (fig. 2). These zones trend 

south;southeast and converge into a single lineament that is 

on strike with the Bear Mountains fault zone (Clark, 1960) 

of the Auburn area. The Swain Ravine lineament fault zone 

displays evidence of late Cenozoic movement in trenches 

excavated for the earthquake studies. Geomorphic expression takes the form of sag ponds, aligned vegetation, 

and springs. The Prairie Creek lineament displays bedrock 

offsets, but no conclusive evidence of Cenozoic movement 

was found in the project area, although Cenozoic movement 

has been demonstrated just south of the Yuba River where 

the Swain Ravine and Prairie Creek zones converge 

(Woodward-Clyde Consultants, 1977; California Department of Water Resources, 1979). Fault-plane solutions 

derived from first-motion studies of the 1975 earthquake 

and aftershocks yield valley-side-down normal faulting 

along fault planes that strike approximately N. 10° W. and 

dip generally about 60° west (California Department of 

Water Resources, 1979, chapter Ill). Field evidence suggests that the fault movement was oblique, with both 

right-lateral and normal, valley-side-down components 

(Sherburne and Hauge, 1975, p. 70). 

The least studied of the three major lineament fault 

zones is the Prairie Creek lineament, which trends northnorthwest through both bedrock and late Cenozoic sediments of the present project area. The lineament is well 

expressed and easily seen in exposed bedrock, but its trace 

becomes obscured and ultimately lost in the surficial deposits between Palermo and Oroville (fig. 2). 

From our fieldwork and stratigraphic reconstruction, 

we conclude that upper Cenozoic deposits, primarily the 

dacite unit and the members of the Laguna Formation, have 

been significantly deformed by monoclinal and anticlinal 

folding, and possibly by faulting. The evidence is indirect. 

We did not observe faults offsetting the described units. 

This should not be surprising because exposure is poor and 

the deformation is either,old enough or the deformation rate 

slow enough, or both, that geomorphic expression of it has 

not been preserved in these erodible, unconsolidated sediments. Our conclusions are based instead on (1) stratigraphic reconstruction, particularly the recognition of and 

location of the relict and exhumed soils developed on the 

lower member of the Laguna Formation, (2) the distribution 

of the surfaces of the units reconstructed from geomorphic 

and topographic evidence, and (3) reconstruction of projected slopes on stratigraphic marker beds and horizons. 

In the paragraphs that follow we use the term slope in 

the sense .of a tectonic inclination of a unit or stratum, not 

in the sense of the original gradient of a deposit. Projected 

slopes should be considered approximate, because datum 

points are widely spaced. Projected slopes were constructed 

using driller's logs, elevations of stratigraphic units s4ch as 

the Nomlaki Tuff Member, and elevations of the uppermost 

outcrops of distinctive units (taken as approximations of the 

upper surfaces of selected units). All slopes in the Feather 

River area were constructed using S. 70° W. as the dip 

orientation. 

The slope of the dacite unit is quite steep at the 

mountain front east and southeast of Oroville, yet relatively 

shallow in the subsurface west of Oroville: the slope on the 

upper surface of the dacite east of Oroville is more than 18 

m/km and apparently reaches a slope of 70 m/km if the 

elevations of dacite outcrops in Long Bar Road are compared with those in the Thermalito Power Canal. West of 

Oroville, slopes of about 4.6 m/km are constructed from the 

elevation of dacite outcrops on the Feather River and depths 

to the dacite in the subsurface. Slopes on the dacite between 

the Feather River and exposures in the borrow pit south of 

the municipal airport are as low as 2. 7 m/km. Much farther 

to the west, in the subsurface near Highway 99, the slope on 

the dacite surface appears to steepen again to about 9 m/km 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G37 
to the west-southwest. Slopes determined from a small 

number of outcrops of the Nomlaki Tuff Member east and 

southeast of Oroville are also very steep, 22 to 29 m!km. 

These steep slopes must also lessen substantially to the west 

in the subsurface, for the slope of the underlying, older 

dacite unit flattens there to 4.6 m!km. In contrast, the 

Nomlaki slopes only about 9 m!km in exposures south of the 

Yuba River and so may be less deformed there. The slopes 

near Oroville suggest that there is a relatively narrow zone 

along the boundary between the valley and mountain front 

that has been significantly deformed. This may have been 

achieved by a monoclinal flexure in the unconsolidated 

Laguna Formation, or possibly by a series of short, en 

echelon or anastomosing fault segments with net valleyside-down movement. A structure-contour map drawn on 

the surface of the dacite shows a narrow, north-southtrending zone of closely spaced contours, at a position that 

suggests that the zone of deformation may be approximately 

on strike with the short north-south reach of the Feather 

River due north of Oroville. This zone in tum is on strike 

with the projection of the Magalia lineament to the north. 

A discordance of slopes on the uppermost gravel bed of 

the upper member of the Laguna Formation north of the 

Feather River compared to south of it may also reflect 

deformation at the mountain front. Reconstructions of the 

surface of this gravel between the Thermalito Power Canal, 

the Butte County Administrative Center, and the Thermalito 

Forebay area yield variable slopes of less than 5.5 m!km. 

Reconstruction of the equivalent gravel surface south of the 

river at Memorial Park Cemetery yields a slope of more 

than 11 m/km. This surface appears to flatten valleyward 

and have a slight concave upward shape (fig. 4A). Differential warping or tilting of this surface is suggested. The 

apparent concavity of this upper surface, along with the 

valleyward shallowing of all slopes on older marker horizons, suggests monoclinal flexure along the mountain front. 

The slopes of older rock units should be steeper than 

original depositional gradients because of ongoing uplift 

and westward tilt of the Sierran block. This has been well 

documented all along the Sierra foothills (Gale and others, 

1939; Davis and Hall, 1959; Arkley, 1962; Marchand and 

Allwardt, 1981); however, slopes of 20 to more than 50 

m/km are clearly anomalous for Pliocene and Pleistocene 

deposits. Slopes calculated for units in the subsurface west 

of Oroville, which average 5 m/km, are much closer to 

those reported for Pliocene and Pleistocene units elsewhere 

along the valley edge (see Marchand and Allwardt, 1981, 

table 1). The outcrop distribution of the lower member of 

the Laguna Formation, with its distinctive relict soil profile, 

is unusual and is best understood in the context of 

mountain-front deformation. At Hewitt Park in Oroville 

(NWI/4 sec. 17, T. 19 N., R. 4 E.; Oroville 7.5-minute 

quadrangle), at an elevation of 200ft (60 m), a remnant of 

a very strongly developed soil with a bright-red argillic B 

horizon ( 10 R Munsell hue) over 4 m thick is preserved on 

what we interpret as the buried original surface of the lower 

G38 Soil Chronosequences in the Western United States 

Laguna '(fig. 4B). This strong soil cannot be associated with 

the upper member of the Laguna, because the outcrop is 

much lower than the projection of the 260- to 300-ftelevation (80 to 90 m) eroded surface of the upper member 

of the Laguna across the river. At the west end of the park 

this paleosol appears to be overlain by gravelly alluvium of 

the upper member. The strong soil profile at Hewitt Park is 

part of a discontinuous geomorphic surface, remnants of 

which extend to South Oroville at elevations of 200 to 260 

ft (60 to 80 m). This geomorphic surface and its exhumed 

soil also lie well below the upper surface of the lower 

member of the Laguna, projected from the higher areas to 

the northeast (fig. 4B). From this evidence, the older units 

appear to slope steeply down to the southwest due either to 

flexure or faulting. Similarly, east of Palermo, the lower 

member of the Laguna Formation with its distinctive relict 

soil lies at elevations as high as 600ft (180 m), and slopes 

steeply to the west (fig. 4C). To the southwest, across a 

northerly projection of the Prairie Creek lineament fault 

zone, the upper member of the Laguna occurs in a synclinelike structure, and farther west it is flanked by an exhumed 

remnant of the lower member. The bedrock exposed between the lower and upper members suggests that the two 

are separated by a fault. The north-south linear outcrop 

pattern of the exhumed lower member of the Laguna and 

other units (fig. 2) suggests that these remnants describe the 

axis of a north-south-trending anticline. The Tehama and 

Red Bluff Formations similarly are exposed well away from 

the mountain front in the northern Sacramento Valley near 

Coming, along the axis of the Coming anticline. The 

overall pattern near Palermo suggests a faulted monocline at 

the mountain front that merges valleyward into a syncline 

and anticline. The timing of deformation at the mountain 

front is important. When did the major deformation occur 

and is it continuing today? The stratigraphic evidence gives 

clues, but it may raise more ,questions than answers. The 

lower member of the Laguna Formation and the dacite unit 

are the most strongly deformed; the upper member of the 

Laguna is less deformed. The intensity of deformation 

appears to decrease from north to south; it is greatest in the 

Oroville area and less at the Yuba River. 

The deformation history is intertwined with the depositional history of the two members of the Laguna Formation. Deformation probably did not begin until late Pliocene 

(early Laguna) time. If deformation had begun much 

earlier, before the lower member was deposited, the slope 

on the dacite might be significantly greater than that of the 

lower member of the Laguna, yet steepened slopes on both 

units are about 18 m!km across the zone of deformation. 

Very steep apparent slopes on the dacite between Long Bar 

Road and the Thermalito Power Canal, however, allow the 

possibility that the dacite is more deformed than the lower 

member of the Laguna. Deposition of the lower member 

may have been completed about 3.2 Ma, and deposition of 

the upper member probably did not begin until about 2.6 

Ma or later. During this interval of nondeposition, defor-
mation apparently began in earnest and canyon cutting 

proceeded rapidly. We conclude this because sediments of 

the lower member of the Laguna east of the postulated 

deformation zone (the projection of the Prairie Creek 

lineament fault zone) were never buried by younger sediments, while areas of the lower member to the west of the 

zone were completely buried by deposition of the upper 

member. This was probably the result both of valleyside-down relative displacement of the lower member and 

of canyon cutting during the time between deposition of the 

two members, so that the fan-shaped flood plain deposits of 

the upper member of the Laguna issued from an apex 

situated at a lower elevation than had the flood plain 

deposits of the lower member. Deformation continued 

during and probably after deposition of the upper member 

of the Laguna, because the slope of the uppermost gravel 

bed is steepened to 11 m/kmjust south of the Feather River, 

and because the upper member is involved in the postulated 

anticlinal folding that extends from Palermo to south of 

Honcut Creek. The stratigraphic evidence suggests that the 

major period of deformation took place betwee~ 3 Ma and 

about 1.0 Ma. Deformation may have begun earlier than 3 

Ma and continued more recently than 1.0 Ma, but we lack 

conclusive evidence to demonstrate this. Harwood and 

Helley ( 1987) bracketed most of the deformation of the 

Chico monocline between about 2.6 and 1.1 Ma because the 

2.6 Ma Ishi Tuff Member of the Tuscan Formation is 

deformed by the monocline, and the 1.1 Ma basalt of Deer 

Creek, which flowed down a canyon cut into the Tuscan, 

was not deposited until after folding had ceased; it in fact 

cascaded over the flexure on its path into the valley. 

Harwood and Helley ( 1987) reported a minimum of about 

365 m of up-to-the-east offset of the basement surface 

across a steeply east dipping reverse fault beneath the Chico 

monocline. The projected trace of the Chico monocline 

passes between the Campbell Hills and South Table Mountain (figs. 1, 2), and may coincide with the Prairie Creek 

lineament fault zone. 

The outcrop pattern of the younger formations and 

drainage patterns between Oroville and Honcut Creek may 

be evidence that anticlinal folding continues to the present 

day. Outcrops of the lower member of the Riverbank 

Formation adjacent to the Feather River and south of 

Oroville (fig. 2) are strikingly linear. Wyman Ravine, 

Wyandotte Creek, and the Feather River all flow southwest 

as they exit the mountain front. Each then turns due south, 

creating a strong north-south alignment of large- and 

small-scale drainages. The gradient of the Holocene flood 

plain of the Feather River between Oroville and Yuba City 

is less than 0.65 m/km, whereas the gradient on the surfaces 

of the lower member of the Modesto Formation and the 

basin deposits to the west-southwest of the river is as much 

as 0.92 m/km. The path of the Feather River may be 

structurally controlled and the river flow constrained to the · 

south, rather than west-southwest to a confluence with the 

Sacramento River north of Sutter Buttes. 

Significant new work is in progress in the Oroville area 

to clarify the interplay between tectonics and late Cenozoic 

sedimentation (Unruh, 1988), and has involved gravity 

surveys, detailed geologic mapping, analysis of old and 

many new well logs, and synthesis of published subsurface 

data. Early findings indicate that bedrock faults indeed have 

expression in offsets in the late Cenozoic sediments south 

and east of Oroville and that these faults were reactivated 

approximately 3.4 Ma (Unruh, 1988). The tectonic regime 

is interpreted to be one of active east-west extension, with, 

for example, the north-south course of the Feather River 

occupying a graben formed by extension. Different faults 

appear to have been preferentially active through time, 

resulting in a progressive shift of the trend of the Feather 

River from west-southwest at 3.4 Ma to due south by 0. 7 

Ma (Unruh, 1989). Work by Unruh is continuing (Unruh, 

1989) in an attempt to relate deformation in the Oroville 

area to patterns and timing of tectonic activity documented 

farther north in the Sacramento Valley by Harwood and 

Helley ( 1987). 

Summary and Discussion of 

Geologic History and Tectonics 

The stratigraphic sequence delineated in this report 

bears certain similarities to that of the American River area 

(Shlemon, 1967a, b; 1972) and to that of the northeastern 

San Joaquin Valley (Marchand, 1977; Marchand and Allwardt, 1981) and yet is unique in several ways (table 1). 

The dacite unit that we have described is clearly 

different from, and younger than, the lower Miocene 

andesitic Mehrten(?) Formation of Creely (1965), with 

which the dacite previously had been correlated. We report 

· an average whole-rock K-Ar age of 3.2 Ma for this unit. We 

have recognized a local stratigraphic sequence of four 

Pliocene to Holocene alluvial units, and we correlate the· 

pre-Holocene alluvial sequence with the informal units of 

the Modesto, Riverbank, and Laguna Formations of Marchand and Allwardt (1981). 

The sequence of geologic events considered in this 

study began with eruption of dacitic lava in the late 

Pliocene. The source of the detritus is not known but is 

likely to have been in the ancestral upper Feather River 

basin adjacent to the ancestral Yuba River drainage. The 

sequence near the Feather River consists of fine tuffaceous 

sediments, overlain by one or more dacitic mudflows, in 

tum overlain by fine tuffaceous sand and silt. Deposition 

was episodic with intervals of nondeposition recorded 

by two or more buried soils within the section. A period of 

nondeposition followed, during which the dacite unit was 

eroded and as much as 10 m of relief appears to have been 

developed on. its surface. Reactivation of Mesozoic shear 

zones along the mountain front probably began during this 

time, resulting in the beginning of valley-side-down relative 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G39 
displacement of the dacite near the point where the modem 

Feather River leaves its bedrock canyon. 

About 3.4 Ma, the Nomlaki Tuff Member was deposited by the ancestral rivers on the Mesozoic bedrock and the 

dacite, signaling the inception of deposition of the lower 

member of the Laguna Formation. On the Feather River, 

the lower member built a fan-shaped flood plain to the 

south-southwest which had its apex near Sycamore Hill 

(northeast of Oroville). Remnants of this deposit at its apex 

now lie at elevations of about 450 to 600ft (135 to 180m). 

A small drainage or embayment to the east of Palermo, 

which was partially blocked from the Sacramento Valley by 

a north-south-trending ridge of Mesozoic bedrock, also 

filled with sediment. Deposits of the stream that appears to 

have been the source of the alluvium in this embayment 

(possibly ancestral Honcut Creek) now crop out at elevations as high as 960ft (290 m) near Bangor. On the Yuba 

River, alluvium of the lower member spread to the west 

from an apex near the point where the modem Yuba enters 

the map area (fig. 2). 

Deposition of the lower member ceased about 3. 2 Ma. 

A period of nondeposition was accompanied by valleyside-down displacement of the dacite and lower member of 

the Laguna. We estimate this period to have been as much 

as 0.5 million years long because an extremely strong red 

soil profile formed on stable parts of the landscape of the 

lower member of the Laguna before it was buried by 

alluvium of the upper member. 

The lower member ·of the Laguna Formation and 

possibly also the upper member was deposited in response 

to tectonic, and not climatic, events: a major period of 

east-west compression and deformation began 2.6 Ma or 

before in the southern Sacramento Valley (Harwood and 

Helley, 1987). The regional compressive stress field and 

zone of deformation has migrated northward through the 

valley from that time to the present (Harwood, 1984; 

Harwood and Helley, 1987). ~he crest of the Sierra Nevada 

in the Carson Pass-Sonora Pass area has been rising at a rate 

which has increased from 0.02 mm/yr 25 million years ago 

to 0.16 mm/yr at present, and almost half of the total uplift 

of the crest over the last 25 million years has taken place 

during the last 5 million years (Huber, 1981). The substantial increase in rate of uplift of the crest beginning about 5 

Ma, combined with regional compressive deformation beginning in the southern Sacramento Valley 2.6 Ma, triggered greatly increased rates of erosion and canyon cutting 

in the northern Sierra, and deposition of the coarse debris 

that we recognize today as the Laguna Formation. The crest 

of the northern Sierra in middle or late Pliocene time was 

probably too low to have sustained ice sheets, should there 

have been glacial epochs in the Sierra at this time as some 

glacial stratigraphic evidence from the high southern Sierra 

suggests, so that a climatic/glacial origin for those deposits 

appears unlikely. The lower member of the Laguna and the 

dacite unit were deformed principally in the time interval 

G40 Soil Chronosequences in the Western United States 

between deposition of the lower and upper members of 

the Laguna or about 3. 2 to 2. 6 Ma; tectonically steepened 

slopes on the lower member of the Laguna and the dacite 

unit appear to be quite similar, whereas slopes on the upper 

member of the Laguna in the same zone near Oroville are 

less than half those of the lower member and the dacite unit. 

Channels were cut deeply into the alluvium of the lower 

member of the Laguna by the Feather and Yuba Rivers in 

the period before deposition of the upper member began. 

The channel cutting was probably enhanced by the westfacing monoclinal flexure of the alluvial and volcanic units 

that was going on-at the same time. When deposition of the 

upper member of the Laguna began about 2.6 Ma, only the 

part of the lower Laguna to the west of the monoclinal 

flexure was buried by alluvium of the upper member. The 

part that was present to the east of the flexure, which was 

several tens of meters higher on the landscape, escaped 

burial, and its remnants persist in the Wyandotte area. Some 

deformation of the alluvial units continued during and 

possibly after deposition of the uppermost gravel bed of the 

upper member had been completed about 1.8 Ma. All units 

appear to be less deformed near the Yuba River, where the 

lower and upper members of the Laguna spread westward 

into a fan-shaped flood plain in which the upper member is 

inset into the lower. Between about 1.5 and 0.45 Ma, 

erosional dissection was the dominant geomorphological 

process along the valley margin. Several erosional geomorphic surfaces were cut into the voluminous sediments of the 

Laguna Formation between the Feather and Yuba Rivers. 

These surfaces may have been caused in part by temporary 

stabilization of base level (either due to climatic or tectonic 

events) and in part by the position of resistant gravel beds 

within the deposits. The last period of erosion exhumed the 

buried surface of the lower member of the Laguna over a 

large area, as overlying sediments of upper member were 

stripped away; soil development resumed on these exhumed 

surfaces. Deposits associated with the erosional events that 

occurred between about 1.5 and 0.45 Ma have not been 

recognized in the area. Detritus shed from the eroding 

landscape was presumably carried farther along the ancestral drainage systems or was buried by younger basin 

deposits. 

The central Sierra and southern Sierra record glacial 

events at least as far back as 800 to 900 ka (Turlock Lake 

Formation) (Janda and Croft, 1967; Marchand and Allwardt, 1981), but in the northern Sierra, lower crestal 

elevations apparently precluded formation of extensive 

glaciers until early Riverbank time. Mathieson and SarnaWojcicki (1982) reported that glaciers probably did not 

advance into Mohawk Lake (in the upper Feather River 

basin) before 450 ka, when the Rockland ash bed was 

deposited in the lakebed sediments, because till or ice-rafted 

boulders are absent from the strata below this time marker. 

Evidence of glacial activity older than 450 ka also is absent 

in the surrounding region. The absence of deposits equiva-
lent to the lower and middle Pleistocene Turlock Lake 

Formation in the FeatQer-Yuba rivers area is consistent with 

this evidence. 

Between 250 ka and possibly 450 ka, deposition of the 

lower member of the Riverbank Formation began, probably 

in response to a middle Pleistocene glacial advance. By this 

time the elevation of the northern Sierra was high enough to 

support extensive glaciers. Interglacial climate brought 

cessation of deposition and a period of landscape stability, 

during which soil formation began. Mainstream incision 

accompanied the interglacial climate, and the lowering of 

base level led to sculpting of the deposits of the lower 

member of the Riverbank Formation as side streams eroded 

into the deposit. In the following glacial period(s), probably 

corresponding to oxygen isotope stage 6 dated at 127 to 190 

ka (Hays and others, 1976; Shackleton and Opdyke, 1976), 

mainstream alluvium of the upper member of the Riverbank 

aggraded to moderate thickness and a thin veneer of 

sediment infilled and buried eroded areas of the lower 

member of the Riverbank Formation, leaving islands of the 

original surface of the lower member surrounded by a 

veneer of sediment of the upper member of the Riverbank. 

In places, alluvium of the upper member of the Riverbank 

buried the eroded remnants of various sideslope and swalefilling soils developed on the lower member of the Riverbank. A corresponding interglacial period of landscape 

stability followed deposition of the upper member, initiating soil development on stable surfaces and incision of river 

channels along main streams. 

Aggradation of the lower member of the Modesto 

Formation began sometime before 40 ka. The Feather River 

followed the course it holds today and an extensive system 

of distributary channels carried flood waters to the southwest across the asymmetrical fan-shaped flood plain to 

deposit clayey alluvium in the ancestral Butte and Sutter 

basins. Near the end of the aggradational cycle, Glacial 

Lake Mohawk was breached, and its lacustrine sediments 

were transported down the Feather River. This lacustrine 

silt and clay spread as a sheet of uniform thickness across 

several hundred square kilometers of the flood plain of the 

lower member of the Modesto. The last stages of aggradation covered the silt to shallow depth with coarser alluvium. 

River incision prior to deposition of the upper member 

of the Modesto cut channels that correspond essentially to 

those occupied by the Holocene flood plains. Aggradation 

of the alluvial cycle of the upper member of the Modesto 

took place about 10 ka. Alluvium was confined to narrow 

flood plains on the Feather, Honcut, and Yuba rivers, and 

did not spread out over the older deposits to form a 

fan-shaped flood plain within the project area. 

Incision of the confined Feather River flood plain 

during early Holocene time swept out much, if not all, of 

the deposits of the upper member of the Modesto, although 

deposits of the upper member were preserved on Honcut 

Creek. Deposition of the major Holocene flood plain of the 

Feather River has been dated at about 3 ka, and radiocarbon ages ranging from 1. 775 ka to 0.45 ka record minor 

channel-building events on the Holocene Honcut Creek and 

reworking of the flood plain surface on the Feather River. 

SOIL CHRONOSEQUENCE SITE SELECTION, 

EXCAVATION, AND SAMPLING 

Nineteen soil pedons were described and sampled from 

11 sites for the chronosequence study (fig. 6). The sites 

were selected after stratigraphic units had been delineated 

on Honcut Creek. All sites are within a 5-km radius and all 

are within 1 km of Honcut Creek. Each site had to meet the 

following criteria: loamy and nongravelly parent materials, 

absence of major lithologic discontinuities, good internal 

soil drainage and absence of duripans, slopes of less than 3 

percent, and minimal disturbance by erosion, deposition, or 

farming. The last criterion eliminated the greatest number 

of potential sites. The lands around Honcut Creek are being 

used for ever more intensive farming, and land leveling and 

deep ripping of subsoils has become the norm. The surfaces 

of some Riverbank-age terrace remnants have been leveled 

by as much as 2.5 m in order to make possible the 

cultivation of rice in diked and flooded fields. Disturbance 

due to agriculture and the small total area of floodplains and 

terraces on Honcut Creek made it difficult to locate suitable 

sample sites. Soil profile sample numbers, stratigraphic 

units, assumed ages and site locations are given in table 5, 

and the individual soil profiles are described in supplementary table 2. 

Sample sites were located in trenches excavated by 

backhoe and by hand, except for the two sites on the lower 

member of the Laguna Formation, which were vertical 

exposures excavated in a bluff adjacent to Honcut Creek. At 

each of the backhoe trench sites, two soil profiles, separated 

by at least 6 m, were described and sampled. This pairedpedon sampling scheme required us to find fewer independent sites that met the criteria stated above than we would 

have had to find without it, while still allowing us to 

measure the variability of replicate soils on same-age 

terraces. We described and sampled the soil profiles in the 

field using standard terms and methods (Soil Survey Staff, 

1975, 1981). From each soil horizon we collected a bulk 

sample weighing about 4 kg for physical and chemical 

analysis, and three to five undisturbed soil peds for bulk 

density determination. We analyzed the soils in the lab 

using methods outlined in Singer and Janitzky (1986). 

Four replicate pedons of Holocene soils were described 

and sampled from two hand-dug pits and two creek-bank 

exposures. C horizons were described and sampled in the 

Holocene soils. The replicate Holocene sites (HON-1 to 

HON-4) are undisturbed and support riparian vegetation. The sites receive some deposition of alluvium during 

floods, but only HON-4 has a distinct layer of overwash. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G41 
Four replicate pedons from the upper member of the 

Modesto Formation were sampled and described from 

two sites. The site of HON-5 and HON-6 has not been 

leveled, is not irrigated, and has been used only for dry 

farming of grains and legumes. The site of HON-7 and 

HON-8 is irrigated and is used to grow vegetable and field 

crops. Care was taken to select a site in this leveled field 

which had been neither cut nor filled by consulting the 

original land leveling plan. The deepest sampled horizons 

were transitional BC horizons of slight pedogenic alteration. 

We had difficulty finding suitable sampling sites on the 

lower member of the Modesto Formation because most of 

the soils formed on the lower member near Honcut Creek 

possess duripans that have formed along the stratigraphic 

boundary that separates the compact silt substratum from 

overlying sediments. Profile HON-9 is of this type and has 

a weak duripan. The profile was described and sampled, but 

at present the profile has been used only to calculate soil 

development indices (SDI). We described two replicate soil 

profiles from a second backhoe trench in a uniform but 

sandy distributary channel deposit (HON-10 and HON-11) 

in order to avoid duripan development. This site has been 

used to dry farm grain crops and has not been leveled. 

Relatively unweathered C-horizons were described and 

sampled in these profiles of the lower member. All Modesto 

Formation sites supported annual and perennial grasses and 

forbs plus scattered oak trees before cultivation. 

Middle Honcut Road 

10, 11 

Lower Honcut Road 

The claypan and hardpan soils of the Riverbank Formation are widely used to grow rice. The landscape, which 

is naturally rolling, must be leveled for rice cultivation, and 

suitable sites were scarce because of the extensive leveling. 

We sampled two replicate pedons from a single site on 

the upper member of the Riverbank Formation (HON-13 

and HON-14). A textural discontinuity was recognized in 

these profiles, but the site met the other established criteria, 

and no other undisturbed, nonduripan sites were found. The 

site has been used to dry farm grain for about 50 years but 

has not been leveled. 

We described and sampled four replicate profiles at two 

sites on nearly level, flat summits of terrace remnants on the 

lower member of the Riverbank Formation (HON-17, 

HON-18, HON-19, and HON-20). Both sites have been 

used in the past to dry farm grain and legumes. The second 

site has been fallow for 15 years. Neither site has been 

leveled. We were able to sample only to the depth of BC 

horizons in these soils. All Riverbank Formation sites 

supported annual and perennial grasses and forbs, and 

scattered oak trees before cultivation. A bluff exposure on 

South Honcut Creek provided the sampling site for two 

pedons in the lower member of the Laguna Formation. The 

two pedons (HON-21, HON-22) are about 10m apart. The 

face of the bluff was cut back about 1 m to expose fresh 

soil. Each profile was described and sampled to a depth of 

about 5 m and an additional sample of C-horizon material 

was collected from each profile at about 12 m. Relief on this 

f 

\ 

\ 

\ 

1 

EXPlANATION 

Sample sites-All numbers prefixed Hon-

+ Holocene alluvium 

Southern Pacific Railroad 1 

(abandoned) 1 

e Modesto Fm. 

A Riverbank Fm. 

• Laguna Fm. 

} 

I 0 1 KILOMETER 

Figure 6. Index map showing sample sites of chronosequence soil profiles. 

G42 Soil Chronosequences in the Western United States 
Table 5. Site locations, assumed ages, and taxonomic subgroups of the soils sampled for the chronosequence 

study 

Profile Geologic Approximate Taxonomic Soil profile site locations, 

number unit age of soiP (ka) subgroup Mount Diablo Base and Meridian 

HON-1 Holocene 0.6 Typic Xerorthents SW1

/4NE1/4 sec. 30, T. 17 N., R. 4 E. 

HON-2 alluvium SW1

/4NW1/4 sec. 31, T. 17 N., R. 4 E. 

HON-3 SW1/4NW1/4 sec. 31, T. 17 N., R. 4 E. 

HON-4 SW1/4NE1/4 sec. 31, T. 17 N., R. 4 E. 

HON-5 Upper member, 10 Typic Haploxerolls NE1/4SW1/4NE1/4 sec. 31, T. 17 N., R. 4 E. 

HON-6 Modesto NE1

/4SW1/4NE1/4 sec. 31, T. 17 N., R. 4 E. 

HON-7 Fonnation SE1

/4SE1/4SE1/4 sec. 22, T. 17 N., R. 4 E. 

HON-8 SE1

/4SE1/4SE1/4 sec. 22, T. 17 N., R. 4 E. 

HON-9 Lower member, 40 Abruptic Durixeralfs 150 m W. of ctr. sec. 24, T. 17 N., R. 3 E. 

HON-10 Modesto 150 m W. of ctr. sec. 24, T. 17 N., R. 3 E. 

HON-11 Fonnation Typic Haploxerolls SE1

/4SW1/4SW1/4 sec. 13, T. 17 N., R. 3 E. 

HON-13 Upper member, 130 Mollie Palexeralfs NE1/4SE1/4 sec. 16, T. 17 N., R. 4 E. 

HON-14 Riverbank NE1

/4SE1/4 sec. 16, T .. 17 N., R. 4 E. 

Fonnation 

HON-17 Lower member, 250 Mollie Palexeralfs NE1

/4SE1/4 sec. 16, T. 17 N., R. 4 E. 

HON-18 Riverbank NE1

/4SE1/4 sec. 16, T. 17 N., R. 4 E. 

HON-19 Fonnation SE1

/4SE1/4SE1/4 sec. 17, T. 17 N., R. 4 E. 

HON-20 SE1

/4SE1/4SE1/4 sec. 17, T. 17 N., R. 4 E. 

HON-21 Exhumed 1,600 Palexerults NW1

/4 sec. 23, T. 17 N., R. 4 E. 

HON-22 lower member, 

Laguna 

Fonnation 

1

See table 3 and text for sources of age estimates. 

surface is less than 1 m near the sampling site, but as much 

as 5 to 6 mover longer distances. The site supports a mixed 

oak-grassland with scattered digger pine and has been used 

only for grazing. 

CHARACTERISTICS OF THE 

SOIL CHRONOSEQUENCE 

Soils form under the influence of five principal state 

factors or environmental variables: climate, organisms 

(principally vegetation in these soils), parent material, 

topography, and time (Jenny, 1980; Birkeland, 1984). 

Jenny ( 1980) formulated the equation for an actual, as 

opposed to idealized, chronosequence as: 

S or s = f (t, cl, o, r, p, ... ) 

in which S is the total soil system, s is an individual soil . 

property, t is the principal factor time, and cl, o, rand pare 

the ineffectively covarying, as opposed to constant, factors 

climate, organisms, relief, and parent material, respectively. What Jenny meant by this formulation was that the 

other four factors need not necessarily be constant or 

invariant for a single-factor study to be valid. If the range of 

variation of a secondary factor is small, or if it is large but 

NW1/4 sec. 23, T. 17 N., R. 4 E. 

of low effectiveness, then that secondary factor will play a 

subordinate role in soil development (Jenny, 1980). In the 

Honcut chronosequence, we think that factors other than 

time have remained relatively similar among sampling sites 

and it is principally the age of the deposit and soil that has 

controlled· soil formation. If factors other than time have 

varied among sites, the variation may be random, which 

adds noise or unexplained variation in soil properties to the 

time factor analysis. The variation may also be systematic, 

which could add a secondary systematic trend to soil 

development that we may or may not correctly recognize 

and interpret. 

Several properties in the Honcut soils change in systematic ways as a function of age, under the influence of 

ongoing pedogenic processes. Some of these properties are 

soil profile morphology, clay content of argillic B horizons, 

and depletion of elements in selected particle-size fractions 

due to weathering of primary minerals. Other soil properties 

change in seemingly nonsystematic ways, possibly reflecting the complicating influence of variation among sites in 

other factors such as climate or parent material. 

We analyzed the soils on selected relict alluvial landscapes at Honcut Creek primarily to evaluate their usefulness in stratigraphic correlation. We briefly discuss herein the evidence for constancy of other factors than time and 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G43 
some of the major trends in soil development. The discussion is intended as an introduction to the many data 

contained in the soil profile descriptions (supp. table 1), 

physical properties (supp. table 2), extractive chemical 

analyses (supp. table 3), clay mineralogy (supp. table 4), 

total chemical analysis of selected particle-size fractions by 

X-ray fluorescence spectroscopy (supp. tables 5, 6) and 

instrumental neutron activation analysis (supp. table 7), and 

the calculated values of the horizon index and profile index 

(supp. table 8). 

Review of State Factors 

Climate 

Present climate and paleoclimates need to be considered in any study of relict soils that have 'developed over 

hundreds of thousands or millions of years. One possible 

source of variation in soil properties is the position of the 

deposits with respect to the present climatic gradient. 

Chronosequence sampling sites on older terraces generally 

lie to the east of and closer to the mountain front than sites 

on the younger terraces, because of the westward progression of alluvial deposition. As a result, sites on the older 

terraces receive approximately 50 to 70 mm more annual 

rainfall than do the sites on the younger terraces. The 

difference in rainfall between sites might therefore constitute a second variable, in addition to time, that has 

influenced soil development. We consider the effect of the 

slight difference in rainfall to be minimal. 

The climate of the project area has not been constant 

over the last 4 Ma. Axelrod ( 1971, 1980) constructed 

paleoprecipitation curves for central California from paleobotanic evidence. Reconstructions from west-central California demonstrate a gradual secular decrease in precipitation from middle to late Miocene time, followed by a large 

increase in precipitation in the Pliocene (fig. 7). A precipitation maximum occurred during the late Pliocene, followed by a steady secular decline through the Pleistocene to 

the Holocene; precipitation in the late Pliocene was about 

1.5 times that of the present day (fig. 7). A wetter climate 

in the late Pliocene may have enhanced development of the 

soils formed on the Laguna Formation relative to soils 

formed on the middle and upper Pleistocene Riverbank and 

Modesto Formations, or a steady secular decline in precipitation through the late Pliocene to the Holocene could 

impose a second systematic factor on soil development. 

Changes in the seasonal distribution of precipitation 

over geologic time may also be important in the assessment 

of influences on soil development. Axelrod ( 1980) reconstructed the middle Pliocene climate at the Turlock Lake 

paleobotanic site in central California based on species 

types and diversity. He reported that the climate in the 

middle Pliocene had a bimodal rainfall distribution with 

significant summer rain, twice the total precipitation of 

today, and a slightly lower mean annual temperature. The 

G44 Soil Chronosequences in the Western United States 

change from the bimodal seasonal rainfall pattern that 

existed in the middle Pliocene to the Mediterranean-type 

pattern that exists today resulted from the uplift of the Coast 

Range and exclusion of inland seas beginning in the early or 

middle Pleistocene. 

Relatively little information is available on ranges of 

precipitation and temperature in the Central Valley during 

climatic fluctuations of the Pleistocene epoch. From examination of the properties and geographic distribution of soils 

in California and the Western United States, however, 

Janda and Croft (1967) and Birkeland and Shroba (1974) 

reasoned that climatic fluctuations during the Quaternary 

did not exert a dominant influence on soil development. For 

example, Janda and Croft (1967) noted that the geographic 

distribution of Alfisols (Soil Survey Staff, 1975) in California and Oregon corresponds almost exactly to the 

present-day distribution of grassland and oak-grassland 

vegetation, and to areas of pronounced summer drought. 

Further, a transect into Oregon showed that the northern 

limit of Alfisols corresponded to a decrease in mean annual 

temperature and an increase in both total annual rainfall and 

proportion of total rain falling in the warm months. This 

suggested to Janda and Croft that the climate during the 

Pleistocene history of soil development in the Sacramento 

and San Joaquin Valleys was probably within the limits of 

climatic conditions that correspond to the present-day distribution of Alfisols. They characterized that climate as 

having a mean precipitation not greater than 860 mm, total 

summer rain less than 130 mm, and no extended periods of 

time in which precipitation was low enough for permanent 

40 

CJ) 30 w 

I 

(.) 

z 

~ 20 

z 

0 

i= 

~ 

a: 

-

-

.I. I I 

~eroly WEST-CENTRAL Santa Rosa ~ 

CALIFORNIA ! 

' Petrified Forest ... -+Santa 

Alam~t, 1 Clara 

' ' , ,~apa Tom'a~~ _ 

Black Hawk l 1 Irvington+ )! Ranch ', // -

',++ ,/ San Bruno 

Mulholland ... Petaluma -

- MIOCENE I PLIOCENE IOU AT. T T 

cEr.nRAL ~t ...• -•-- - SIERRA NEVADA <:.1'~~/ San Joaquin Mtn. - hl 40 a: 

a.. 

_I 

<( 

- Table Mt~----- '----.,rt. Reba,/ 0 /,------ - ... _ ·--, --. ', .--· ~0~-- •• ----

~ 30 

z 

<( 

20 -

-

10 

12 

-- -- ----· of? • ~ •• :\. '---,, ReQ1ingto.~ Hill ~/~--~~o=. .. -- '·-,<~·' ... ::::::::::)-::;·/ -

'•,, v0 _, Turlock Lake -

-----------·------ -

Oakdale 

MIOCENE I PLIOCENE IOUAT. I I 

10 8 6 4 2 0 

AGE, IN MILLIONS OF YEARS 

1000 

800 CJ) 

a: 

w 

~ 

w 

600 ~ _I 

_I 

~ 

400 ~ 

z 

1200 Q 

!;( 

1-' 

1000 Q; 

(.) 

w 

a: 800 a.. 

_I 

<( 

::::> 

600 z 

z 

<( 

400 

Figure 7. Plots of estimated rainfall from Miocene to 

Quaternary time in west-central California and central 

Sierra Nevada. From Axelrod (1980). 
accumulation of lime in subsoils. Thus they concluded that 

the Alfisols which have formed on alluvial terraces in 

California are the product of long periods of weathering 

under conditions of climate and vegetation similar to the 

present, and that Quaternary climatic fluctuations in the 

Central Valley do not appear to have altered significantly 

the basic direction of pedogenesis on the alluvial landscapes. 

Organisms 

Pre-settlement vegetation on wet flood plains was a 

woodland-savanna populated with perennial grass, valley 

oak (Quercus lobata), and cottonwood (Populus fremontii). 

Low alluvial terraces had (and some still have) perennial 

grass, scattered valley oak, and interior live oak (Quercus 

wislizenii), whereas high terrace remnants on the margin of 

the valley supported perennial grass, interior live oak, blue 

oak (Quercus douglasii), a few digger pine (Pinus sabiniana), and buckeye (Aesculus californica). Little information is available on the movement of ecotone boundaries in 

this area during the Pliocene and Pleistocene; however, the 

soils have probably formed under a grass-oak savanna 

throughout their development. 

Parent Material 

The alluvial parent materials of the soils in the chronosequence are moderately stratified loam, silt loam, and 

fine sandy loam (supp. table 2). The parent materials 

generally are high in silt, fine sand, and very fine sand and 

are low in clay and coarse sand. Textural and mineralogical 

variations and discontinuities were recognized both within 

and between sampling sites. Stratification of texture most 

directly enhances or impedes the movement of water and, in 

tum, the movement of soluble or particulate weathering 

products in soils. Stratification, therefore, may control the 

depths at which major horizons form. Mineralogical stratification probably has a more complex and subtle effect on 

soil development through its influence on the types of 

mineral weathering reactions and on clay formation. The 

overall texture of a parent material, the proportion of 

gravel, sand, silt, and clay, can affect rates and processes of 

soil development because small particles tend to be more 

reactive to chemical weathering than coarse particles. Over 

the same period of time, then, a fine-textured parent 

material may develop a stronger soil profile than a coarsetextured parent material. 

Parent material textures vary among the chronosequence soils more than would be considered ideal. We 

illustrate this with plots of the percentage of sand, calculated on a clay-free basis to minimize the influence of 

pedogenesis, versus soil depth (fig. 8A-F). The clay-free 

sand content is useful for visualizing differences in initial 

texture within and between soil profiles .. Busacca (1982) 

demonstrated that the ratio of silt to sand on a clay-free 

basis, and the ratio of medium sand to fine plus very fine 

sand, on a silt- and clay-free basis, are also useful to 

distinguish lithologic discontinuities and depositional sequences in these alluvial parent materials. The percentage 

of sand, on a clay-free basis, ranges from about 20 to 75, 

considering all A and B horizons together, and ranges as 

high as 90 in some deep gravelly BC horizons (fig. 8). The 

gravel content is less than 10 percent in the A and B 

horizons of all soils, except that the deepest Bt subhorizons 

of the soils formed on the lower member of the Laguna 

Formation have up to 30 percent gravel (supp. table 2). The 

gravel content is from 5 to 70 percent in the deep BC 

horizons of the soils formed on the lower member of the 

Riverbank Formation and the lower member of the Laguna 

Formation. 

Replicate profiles of soils formed on each chronosequence member are generally similar to one another in 

texture and in the position of lithologic discontinuities 

within the profiles: the soils formed in Holocene alluvium 

fine upward (fig. 8A). The two profiles sampled from 

natural levee deposits are more stratified than the two 

profiles sampled from overbank deposits. The parent materials of the four replicate profiles sampled from the upper 

member of the Modesto Formation are quite uniform and 

similar to one another above a depth of 200 em (fig. 8B), 

but they become progressively more coarse with increasing 

depth below this point as basal channel sands of this 

depositional cycle are encountered. Clay-free silt contents 

of 55 to 75 percent in the upper 200 em of these soils 

corresponds to silt loam parent material textures. These are 

the finest textured and least stratified parent materials in the 

chronosequence. In contrast, the two replicate soil profiles 

sampled from a distributary channel deposit of the lower 

member of the Modesto Formation have the coarsest parent 

material textures of any of the chronosequence soils (fig. 

8C). The difference in texture between deposits of the upper 

and lower members of the Modesto Formation may well 

have influenced relative rates of soil formation at comparable stages, with the rate of delvelopment being faster in the 

finer textured materials. 

The two soil profiles sampled on the upper member of 

the Riverbank Formation show abrupt changes from fine to 

coarser textures at about 125 and 150 em, which are 

superimposed on overall fining-upward patterns (fig. 8D). 

Parent material textures are silt loam above the discontinuity and stratified loam and sandy loam below it. The argillic 

B horizon has developed just above the discontinuity in the 

two replicate profiles, probably as a result of impeded 

downward flow of water at the discontinuity. 

The four soil profiles sampled on the lower member of 

the Riverbank Formation also have a major textural discontinuity (fig. 8E), but it is at 160 to 200 em in the profile, and 

the parent material texture above the discontinuity is loam 

rather than silt loam. In the soils of the lower member, the 

maximum development of the argillic B horizon is just 

above the discontinuity, again suggesting that the disLate Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G45 
continuity controlled depth and degree of development of 

the B horizon. 

This pattern, in which gravelly or sandy materials fine 

upward and are overlain abruptly by loam or silt loam 

materials, is shared by the soils formed on the upper 

member of the Modesto Formation and those on the upper 

and lower members of the Riverbank Formation (fig. 8B, 

D, E). We interpret each of these to be deposits of point-bar 

C/) 

a: 

w 

1-

w 

::::iE 

~ 

z 

w 

(.) 

~ 

z 

0 

N 

a: 

0 

::r: 

...J 

5 

C/) 

LL 

0 

w 

C/) 

< CD 

0 

1-

J: 

1-

0... 

w 

0 

200 

0 

100 

200 

300 

400 

0 

100 

200 

Holocene alluvium 

B 

Upper member 

Modesto Formation 

c 

Lower member 

Modesto Formation 

20 40 60 80 

PERCENT SAND, CLAY-FREE 

Figure 8. Percent clay-free sand versus depth in 

replicate soil profiles formed in Holocene alluvium 

(A), upper (8) and lower (0 members of the 

Mbdesto Formation, upper (D) and lower (E) members of the Riverbank Formation, and lower (F) 

member of the Laguna Formation. Profile numbers 

are prefixed HON- . See figure 6 for location of soil 

profiles (1-22). 

G46 Soil Chronosequences in the Western United States 

100 

or basal-channel gravel and sand of lateral accretion overlain by overbank loam and silt loam of vertical accretion. 

Most of the soils formed on the upper member of the 

Riverbank Formation at sites away from Honcut Creek have 

formed in a thin ( <2 m) veneer of alluvium deposited over 

an erosional surface cut into silt strata of the lower member, 

rather than having formed in alluvium of a single age and 

depositional cycle. Soils of the Yokohl series (Typic 

200 

300 Upper member 

Riverbank Formation 

0 

E 

100 

200 

300 

400 Lower member 

Rive~bank Formation 

0 

F 

100 

200 

300 

400 

Lower member 

soo Laguna Formation 

0 ~ ~ ~ M 100 

PERCENT SAND, CLAY-FREE 
Durixeralfs)6 have formed in the veneer of upper member 

sediment, and soil development extends across the interface 

into the older materials. The interface with the older silt has 

created a sufficient barrier to water movement that a duripan 

formed in this soil. 

Both of the soils sall}pled from the lower member of the 

Laguna Formation . appear to have formed in a relatively 

uniform sandy loam parent material similar in texture to the 

alluvium at the sampling sites of the soils on the lower 

member of the Modesto Formation (fig. 8C, F). The 

original texture of the parent materials in the soils of the 

lower member of the Laguna may be difficult to interpret 

from particle-size analyses because the extreme depth and 

degree of weathering in these soils may have altered 

appreciably the sand and silt content of the horizons. 

We analyzed the elemental composition of the fine and 

coarse silt fractions (2-20 f.Lm and 20-50 J.Lm, respectively) 

using X-ray fluorescence spectroscopy (XRF) (supp. table 

6), and we analyzed the elemental composition of the 

silt-plus-clay fraction (<50 J.Lm) of selected horizons by 

XRF and instrumental neutron activation analysis (INAA) 

(supp. tables 5, 7). Our primary purpose in doing this was 

to examine pedogenic changes in these reactive size fractions as a function of soil age, but first we used this data to 

examine the initial uniformity of elemental composition of 

these fractions both within single deposits and among the 

chronosequence members. Although we discuss it only 

briefly here, our analysis of the uniformity of elemental 

composition in the parent materials was a critical first step 

in correctly reconstructing pedogenic changes in the elemental chemistry of these size fractions. 

We use one of the soil profiles formed in Holocene 

alluvium to test and illustrate the effect of textural stratification (fig. 8A) on elemental composition (table 6), because 

pedogenic changes in elemental composition are minimal at 

this early stage of soil development. We can think of the 

elemental composition of a particle-size fraction as a proxy 

for the mineralogical composition of that fraction. Depositional processes can affect the initial mineralogy of a 

sedimentary layer, and pedogenesis, or soil development, 

also can affect the mineralogy and elemental composition 

through dissolution and alteration of the primary minerals. 

We have found generally that the textural stratification 

in these parent materials, even when severe, does not have 

a strong effect on elemental composition of specific size 

fractions. This is illustrated in table 6. The silt-to-sa~d ratio 

in the horizons of a Holocene soil vary by a factor of almost 

5 down the profile, whereas ratios of calcium to zirconium 

and iron to zirconium in fine and coarse silt of the same 

horizons vary by a factor of no more than 1.4. Other 

elemental ratios in these horizons and elemental ratios in 

little-altered BC and C horizons of other soils confirm 

6 The Yokohl series was classified as Abruptic Durixeralfs in the Yuba 

area soil survey, but official series classification is as above. 

Table 6. Comparison of the effect of stratification in a 

Holocene soil profile1 on texture versus elemental composition 

Basal Ratio of Ratio of Ratio of 

Horizon depth silt to (Ca@)xlOO (Fe.O/Zr)xl 00 

(an) sand' line silt' coarse silt' line silt' coarse silt' 

c 17 .54 3.12 2.44 7.70 2.92 2A 32 1.26 3.05 2.54 7.61 2.97 2AC 49 1.83 3.11 2.34 1.55 2.71 2C 86 138 3.05 2.46 7.63 3.03 3C1 113 .63 2.94 1.98 7.65 2A5 3C2 147 39 2.80 1.86 7.20 2.23 HJL4 4.7 1.1 1.4 1.1 1.4 

'Prafilc HON-4. 

'Calculated 011 • clay-free buiJ. 

'Fine lilt iJ 2-20jllll and come lilt iJ 20-SOjlm. 

'Ratio of lbe bisbest value in a c:olU11111 10 lbe lowest value in co1amn. 

this finding. Apparently the grading of grain sizes and of 

mineralogy are somewhat independent in this alluvial system. 

Element concentrations generally are less affected by 

textural stratification in the fine-silt fraction than in the 

coarse-silt fraction. The ratios of calcium to zirconium and 

iron to zirconium in the horizons of the Holocene soil vary 

by only a factor of 1.1 in the fine-silt fraction but by a factor 

of 1.4 in the coarse-silt fraction (table 6). 

In the soils formed on the lower member of the 

Modesto Formation, an abrupt textural discontinuity separates the base of the sandy channel deposit from the 

underlying mica-rich silty sand (between C and 2C horizons 

in table 7). Although the discontinuity shows as rather large 

changes in the concentrations of Si, AI, Ca, Zr, and Cr in 

the coarse-silt fraction, there is but scant evidence of the 

discontinuity in the concentrations of these elements in the 

fine-silt fraction. 

The elemental· composition of the soil parent material 

not only varies within individual profiles, but also varies 

between deposits or chronosequence members. The mineralogy of the alluvium deposited by Honcut Creek has 

changed slightly over the time span of the chronosequence, 

and the elemental composition of the alluvium reflects this 

also, although the range of variation is perhaps not greater 

than that found in other similar alluvial settings. Table 8 

summarizes the elemental composition of the coarse- and 

fine-silt fractions averaged from the least altered horizons in 

one soil profile from each member of the chronosequence. 

Deep BC and C horizons were used in these calculations for 

all but the Holocene soils to minimize the effects of 

pedogenic alteration. All six horizons were averaged for the 

Holocene soil, because the degree of alteration of the A and 

C horizons was judged to be minimal. 

Concentrations of Na, K, and Cain fine silt and of Na 

Mg, Si, K, and Ca in coarse silt (table 8) identify th~ alluvium of the lower member of the Modesto as having had 

a different source than the other chronosequence members. 

Cu, Ni, and Cr (supp. table 6) also are good indicators of 

the different source area. The elemental chemistry in this 

case confirms field evidence that the alluvium at the sample 

site for soils of the lower member of the Modesto Formation 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G47 
Table 7. Comparison of the effect of textural stratification on elemental composition of coarse versus 

fine silt (20-50 ~m versus 2-20 ~m) in a soil profile (HON-10) on the lower member of the Modesto 

Formation 

Basal Percent Percent 

Horizon depth Si02 Al 20 3 

(em) coarse fine coarse fine 

silt silt silt silt 

BC 150 62.6 57.0 15.4 18.9 

c 205 61.9 56.5 15.6 18.6 

2C 225 60.1 56.6 16.8 18.9 

was deposited by the Feather River and not Honcut Creek. 

The data in table 8 demonstrate that the other five chronosequence members did have Honcut Creek as their 

source. 

The differences in parent material composition among 

chronosequence deposits and compared to fresh stream 

sediment are large enough (table 8) that we calculated 

pedogenic gains and losses in these size fractions using the 

actual C horizon composition of each soil individually. We 

did not average compositional values among deposits for 

our calculations. We also placed emphasis on results 

obtained from the fine-silt fractions because of our finding 

that initial textural stratification within a deposit or profile 

caused only relatively small perturbation in elemental composition. In doing these two things we have recognized and 

attempted to minimize the effect that stratification within a 

deposit, and variation in mineralogy between deposits, 

would have on our calculations of pedogenic change over 

time. 

Soil Development 

Many of the morphological, physical, chemical, and 

mineralogical soil properties of the chronosequence change 

systematically with soil age. For example, the soils become 

red, clay forms or accumulates in argillic horizons, and 

profile depth increases to more than 5 m (table 9), although 

for each of these, the perfection of the trend seemingly is 

interrupted by variation in factors other than soil age. 

Different soil properties yield similar or complementary 

information because the multitude of changes in soil properties over time are interdependent (Busacca, 1982). For 

example, we can deduce that the formation of secondary 

clay minerals should be proportional to the dissolution or 

transformation of primary minerals. As a result we expect 

the clay content and the morphology of B horizons, and the 

elemental composition of primary mineral fractions to each 

change systematically with soil age under the influence of a 

linked set of pedogenic processes. This is valuable in terms 

of soil correlation because an interpretation based on the 

analysis of one soil property can be checked against several 

other soil properties. 

We have selected soil morphology, as quantified by the 

soil development index of Harden (1982a), mineralogy of 

G48 Soil Chronosequences in the Western United States 

Percent 

CaO Zr (ppm) Cr (ppm) 

coarse fine coarse fine coarse fine 

silt silt silt silt silt silt 

5.1 2.5 263 140 331 278 

5.2 2.6 275 137 351 299 

4.7 2.6 237 130 271. 252 

the clay-size fraction ( <2 J.t.m), and elemental composition 

of silt fractions (2-20 J.t.m and 20-50 J.t.m) to illustrate some 

of the systematic changes in the soils over time and also to 

illustrate some nonsystematic variation imposed by change 

in other soil-forming factors. 

Soil Development Index 

The soil development index (Harden, 1982a) has been 

calculated for the chronosequence soils (supp. table 8),-and 

it has proved to be a very sensitive measure of soil 

development. We use the index here to illustrate the major 

developmental steps in the chronosequence soils. The soil 

development index converts the morphological properties of 

soils, as recorded in standard field descriptions, into a 

numerical rating so that soils with differing degrees of 

development can be compared. 

The detailed procedure for calculating the soil. development index and the several ways in which the index can 

be used are discussed by Harden ( 1982a) and Harden and 

Taylor (1983). Eight soil properties are used in the original 

formulation of the soil development index: ( 1) rubification 

(reddening of color hue and brightening of chroma), (2) 

total texture (texture plus wet consistence), (3)'structure, (4) 

dry consistence, (5) moist consistence, (6) clay films, (7) 

melanization (decrease in color value of A horizons due to 

the buildup of org~nic matter), and (8) pH. We substituted 

laboratory-determined texture and pH for the fielddetermined equivalents, as did Harden (1982a). With this 

choice of properties it is clear that this specific formulation 

of the index has been designed principally for well-drained, 

freely oxidized soils in which argillic horizon development 

is a major process. Harden and Taylor (1983) added 

color-paling, which is the inverse of rubification, and 

color-lightening, which is the inverse of melanization, 

specifically for soils that accumulate secondary calcium 

carbonate. 

The soil development index uses a point system in 

which points are assessed in increments of ten for differences between a property in a soil horizon and that property 

in the soil's parent material. In the case of dry consistence, 

ten points are assessed for each step from loose to soft, to 

slightly hard, to hard, to very hard, to extremely hard: if a 

soil B horizon has a dry consistence that is extremely hard 
Table 8. Average values of element concentration (percent) in coarse (20-50 !J.m) and fine (2-20 !J.m) silt fractions of BC 

and C horizons of the chronosequence soils 

[n, number of samples] 

Sample data' Na20 MgO Al20 3 Si02 K20 CaO Ti02 Fe20 3 Zr 

(ppm) 

Fine silt (2-20 fllll) 

Holocene alluviwn (HON-4), 21-26 2.49 5.15 18.68 52.6 0.805 4.58 1.32 11.52 152.5 

n = 6, (A's, C's)l 

Upper member, Modesto Fm. (HON-5), 2.97 5.50 18.31 53.6 .605 3.98 1.22 10.64 165.5 

32-33, n = 2, (BC1, BC2) 

Lower member, Modesto Fm. (HON-10), 2.17 5.79 18.80 56.7 1.85 2.57 1.06 9.23 135.7 

63-65, n = 3, (BC, C, 2C) 

Upper and lower members, Riverbank 3.18 5.97 17.46 56.5 .875 4.13 .902 9.23 115.3 

Fm. (HON-14,-18), 93, 94, 109, 110, 

n = 4, (deep BCt's and CB) 

Lower member, Lagnna Fm. 141 2.16 31.56 4

21.57 51.3 .88 3

3.30 .87 11.74 120 

(HON-21), 141 (3BC and deep C) 5142 3.20 5.47 19.17 4

52.1 .86 4.54 1.21 10.95 128 

Fresh stream sediment, 156 2.78 4.99 16.09 56.8 .74 5.20 1.33 9.68 137 

Coarse silt (20-50 flDl) 

Holocene alluviwn6 3.95 4.24 15.52 56.2 .617 7.34 1.46 8.80 7

329 

(295) 

Upper member, Modesto Fm. 4.41 3.48 15.24 58.7 .530 6.43 1.28 7.69 280 

Lower Member, Modesto Fm. 3.27 4.41 15.30 62.2 1.12 5.04 1.11 7.14 267 

Upper and Lower Members, 4.34 3.24 14.78 60.2 .72 6.95 .75 6.65 7317 

Riverbank Fm. (260) 

Lower member, Lagnna Fm., 5141 3.80 3.70 4 16.16 57.7 . 4.78 7.51 .74 4

8.17 4

300 

142 4.89 l2.13 15.61 59.0 .66 7.19 1.14 7.14 260 

Stream sediment, 156 4.48 2.91 14.70 59.4 .57 7.87 1.23 6.76 262 

'Geologic unit (profile number), sample numbers of horizons used in calculating average values, number of horizons used, and (type of 

horizons used). 2A horizons were averaged with C horizons in Holocene soil (HON-4) where little or no alteration of elemental composition has yet occurred. 3Concentration depleted by weathering losses. 

4Concentration enhanced by weathering losses of other elements. 5Values for samples 141 and 142 not averaged but reported separately because sample 141, a 3BC horizon, has been altered by soil development. 6

Samples averaged for coarse silt fraction are as above for fine silt fraction. 1

'Z:t concentration is erratic because of stratification. Values shown in parentheses are those used as estimated concentrations in C horizons 

for calculations of element losses and gains in soil profiles using Zr as a stable element (see text). 

and the parent material is loose, 50 points are tallied for the 

property in that horizon. Once all properties have been 

evaluated for each horizon in a profile, the quantified 

properties are normalized to a scale that ranges from 0 to 1, 

generally by dividing by the maximum points that could be 

assessed for each property. When the normalized values of 

the properties are summed for a horizon and divided by the 

number of properties, a dimensionless quantity between 0 

and 1 is obtained called the horizon index. The horizon 

index is a measure of the development of an individual 

horizon relative to its parent material, and the horizons of a 

profile can be studied as functions of soil depth or soil age. 

When the horizon index for each horizon is multiplied by 

the thickness of the horizon, and the values (in indexcentimeters) are summed for an entire soil profile, a single 

quantity, the profile index, is obtained. The profile index of 

a soil is a measure of the degree of development of the 

morphology of that soil. Profile indices of two or more soils 

can be compared, and soil development can be studied as a 

function of soil age. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G49 
Graphs of the horizon index versus soil depth for the 

chronosequence soils provide a visual summary of the 

progression of soil development over time (fig. 9A-F). The 

horizon index values are highest in the A horizons of the 

Holocene soils and decrease with depth (fig. 9A). Melanization and development of soil structure, which is granular in 

these A horizons, contribute to the horizon index values. 

Individual Holocene profiles are highly stratified, and this is 

reflected in the horizon index plots. C horizons have 

nonzero horizon indices due to previous weathering of the 

alluvium deposited in some of the strata and also apparently 

to rapid oxidation of the sediments once in place. The 

average profile index for the four replicate Holocene profiles is 12 index-em (table 10). 

A subsoil cambic B horizon has developed in the 10-ka 

soils of the upper member of the Modesto Formation, and 

this is reflected in the depth of plots of the horizon index 

(fig. 9B). The maximum values of the horizon index are in 

the B, not A, horizons of these soils, and this is primarily 

due to rubification (reddening and brightening of soil color) 

and the development of structure and clay films. Large 

values of rubification and structure extend to more than 2 m 

in these soils and contribute to large horizon indices at these 

depths (fig. 9B). As a result of the large horizon index 

values at depth, the profile index, averaged for the four 

replicate profiles (the profile index is equivalent to the area 

under the horizon index plots), is 45 index-em, a value that 

is higher than our expectation and higher than the profile 

index for comparable soils of the upper member of the 

Modesto Formation on the Merced River (table 10). 

The 40-ka soils on the lower member of the Modesto 

Formation have subsoil argillic horizons. The maximum 

value of the the horizon index in the B horizons of the soils 

of the lower member of the Modesto is 0.4, compared to 

0.27 in B horizons of soils of the upper member (fig. 9B, 

C). The B-horizon maximum is more sharply defined in the 

soils of the lower member than it is in those of the upper 

member, because of greater clay accumulation (total texture 

and clay films) and more strongly developed soil structure 

(structure property). 

The presence of a silty substratum and differences in 

parent material textures between replicate soil sampling 

sites of the lower member of the Modesto appears to have 

caused differences in soil development between sites. Two 

of the soils of the lower member formed in a coarse sandy 

loam parent material (fig. 9C, profiles 10 and 11), and the 

third soil formed in a silt loam parent material (profile 9). 

All three soils overlie a dense silt substratum, the sandy 

soils at about 2 m, the silty soil at about 1.3 m. The silt 

substratum restricted deep percolation of water and effectively stopped soil development beneath the discontinuity, 

in striking contrast to the deep development of the freely 

drained soils formed on the upper member of the Modesto 

(compare fig. 9B, C). In 40,000 years, the finer textured 

parent material in profile 9, which has a larger proportion of 

weatherable silt- and clay-sized minerals and a higher water 

G50 Soil Chronosequences in the Western United States 

Table 9. Selected morphological and physical properties of 

the chronosequence soils 

Geologic 8-horizon Pedogenic clay Total depth 

unit color• formecP (g/cm2) of weatheringJ (em) 

Holocene alluvium lOYR 3{3 -1.6 40 Modesto Fonnation 

Upper member 7.5YR 3/4 4.5 116 

Lower membc2' 5-7.5YR 3/4 9.3 •tso 

Riverbank Fonnation 

Upper member 5YR 4/6 51.0 263 

Lower membc2' 2.5YR 3/6 43.9 >288 

Laguna Fonnation 

Lower membc2' lOR 3/6 105.5 >500 

'Reddest hue and highest chroma reported from B horizons of replica!e soil profiles of 

each stratigraphic unit A horizon colors used for Holocene soils. 

2Calrulalion of pedogenic clay formed (g clay/cm2 land lllllfacelprofile) based on: present 

clay content of each horizon, estimated original clay c:onten1 of horizons, horizon thickness, and 

bulk density. Replicate soil profiles averaged. 

'Depth of deepest A or AC horizon among Holocene replicate soils; average depth to 

bottom of Bw horizons used for soils on upper Member of Modesto Formalion because of 

uncertainty as to bottom of solum; average depths to bottom of BC horizon or greatest depth 

exposed in BC maleri.al among replicate soils for all others. 4

Depth of weathering restricted by subsoil lithologic discontinuity. 

holding capacity, has formed a soil with a moderate argillic 

horizon and with a duripan above the shallow discontinuity. 

In apparently the same period of time, the sandy parent 

material in profiles 10 and 11, with a smaller proportion of 

weatherable silt- and clay-sized minerals and a lower water 

holding capacity, has formed soils with weak argillic 

horizons. These differences in B-horizon development are 

apparent in the plot of horizon index versus depth (fig. 9C) 

and also in the profile index: the average profile index for 

the sandy soils of the lower member of the Modesto is 48 

index-em, compared to 56 index-em for the silty soil. 

By this measure, the difference in soil development due to 

difference in texture (and drainage) is about 17 percent at 40 

ka. 

The soils developed on the two members of the 

Riverbank Formation have strongly developed, clay-rich 

argillic B horizons, and significant soil development extends to more than 3m (fig. 9D, E). The maximum value of 

the horizon index is similar in the B horizons of both 

members, about 0.52, compared to 0.4 and 0.27 in the B 

horizons of the soils of the lower and upper members of the 

Modesto, respectively. Lithologic discontinuities in soils of 

both Riverbank members were recognized from field evidence and particle-size data. The discontinuities, silt loam 

over sandy loam at 1. 5 to 2 m in the upper member and 

loam over gravelly sandy loam at 2 m in the lower member, 

appear to control the position of maximum B horizon 

development (fig. 9D, E). Soil development beneath each 

discontinuity, as measured by the horizon index, decreases 

markedly with depth into the coarser materials. Retention of 

water in the finer sediments because of impeded percolation 

across the discontinuity appears to have concentrated soil 

development in the B horizons just above the lithologic 

break (compare figs. 8D, E and 9D, E). 

Soils on the lower member of the Riverbank are distinct 

morphologically from those on the upper member: the 
200 

Holocene alluvium 

300~--~----~----~ 

B 

Upper member 

Modesto Formation 

Lower member 

Modesto Formation 

0 0.1 0.2 0.3 0 0.1 0.2 0.3 0 0.1 0.2 0.3 0.4 0.5 

HORIZON INDEX 

0 D 

C/) 100 

a: 

w 

1-

w 

~ 

i= 

z 

w 

u 

~ 

z 

200 

2 a: 300 

0 

J: 

...J 

5 

(/l 

Upper member 

Riverbank Formation 

~ 400~----L-----L-----~--~----~ 

0.1 0.2 0.3 0.4 0.5 0.6 0.1 w 

(/l 

<( 

CD 

~ 

iE 

a. 

w 

0 

0.2 

HORIZON INDEX 

Lower member 

Laguna Formation 

0.3 0.4 0.5 0.6 

HORIZON INDEX 

E 

0.7 

Lower member 

Riverbank Formation 

0.2 0.3 0.4 0.5 0.6 

Figure 9. Horizon index versus depth of 

soil horizons in replicate soil profiles 

formed in alluvium ·Of chronosequence 

members. Profile numbers are prefixed 

HON- . See figure 6 for location of soil 

profiles (1-22). 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G51 
soils on the lower member are redder (table 9) and the 

position of maximum B horizon development is deeper than 

on the upper member. In the field, thes·e differences were 

useful in distinguishing the two soils; nevertheless, in terms 

of the maximum value of horizon index (fig. 9D, E) and in 

terms of the profile index (table 10), the soils are quite 

similar in degree of development. 

The exhumed soils formed on the lower member of the 

Laguna Formation display an extreme stage and depth of 

soil development (table 9); for example the horizon index 

reaches 0.65 in the B horizon, and it remains greater than 

0.3 at a depth of 5 min the soils (fig. 9F). Particle-size data 

show that these soils formed in uniform loam or sandy loam 

parent material (fig. 8F), and the horizon index depth plots 

indicate smooth changes in soil development from A to B to 

BC horizons. The average profile index for these soils is 

223 index-em (table 10), more than double the profile index 

of the next most strongly developed soils on the lower 

member of the Riverbank Formation. 

The very great depth and extent of development of the 

soils of the lower member of the Laguna Formation is 

consistent with the geological evidence that the first 0.5 

million years of their development, before burial, took 

place in the wetter climate of the late Pliocene. We might 

conclude that these soils are so strongly developed because 

of their early history. Perhaps the gravel abundance in these 

soils (up to 70 percent), with the attendant decrease in water 

holding capacity per unit of soil depth, also allowed deep 

percolation of the available soil water. We believe it likely, 

as argued by Arkley for a very deep soil in California ( 1981 , 

p. 672), that the deep weathering of soils is increasingly a 

function of the wettest years as soils grow older, because 

with great age the total number of infrequent deep-wetting 

years becomes very large. 

It is informative to overlay depth plots of the horizon 

index for all six chronosequence members (fig. 10). Each 

depth plot is an average of the replicate soil profiles for that 

member. When they are displayed in this way, the changes 

in soil morphology with age can be compared directly. The 

development of a B horizon manifests itself within 10,000 

years and the B horizon becomes stronger, thicker, and 

better defined throughout the 1.6 million years of soil 

development studied here. Of the eight soil properties 

tracked in the index, clay films, structure, rubification, and 

total texture contribute most significantly to the increasing 

horizon index in B horizons. 

A horizons do not appear to develop as systematically 

as B horizons over the full span of the chronosequence. The 

horizon index of A horizons does increase from Holocene 

soils to soils of the upper member of the Modesto to the 

soils of the lower member of the Modesto (fig. 10), largely 

due to melanization (decreasing color value) and rubification. The horizon indices of the A horizons of the soils of 

the upper member of the Riverbank are low, comparable to 

those in the Holocene soils. The A horizons of these soils 

have weak structure and are not very dark. There is 

G52 Soil Chronosequences in the Western United States 

Table 10. Comparison of profile indices (in index-em) 

for soils from Honcut Creek and the Merced River 

that are approximate stratigraphic equivalents 

Geologic unit Honcut Merced 

Creek River1 

Younger Holocene alluvium 12 17 

(<1000 yr) 

Older Holocene alluvium 2_ 24 

(>3000 yr) 

Modesto Formation 

Upper member 45 27 

Lower member 3

51 (56) 69 

Riverbank Formation 

Upper member 102 101 

Lower member 41Q8 (113) 125 

Turlock Lake Formation 2_ 148 

Laguna Formation 

Upper member 2_ '264 

Lower member '223 6_ 

1

Data from Harden (1982a). 

2No equivalent soil described at Honcut Creek. 3First value is average of two soils in coarse distributary 

channels of lower member and one soil in silty overbank materials 

of lower member. Second value from silty soil only, probably 

forms a more suitable comparison with soils developed in silt-loam 

materials on upper member of Modesto. 4 108 is average of four replicate soils formed on middle 

member, 113 is average of two most strongly developed soils of 

four. 

'Soil at Merced River was estimated by Marchand and Allwardt (1981) and Harden (1982a) to be 3.0 Ma; we estimate that 

soil at Honcut Creek is 1.6 Ma because, although deposit is older, 

it has been buried for part of that time. See text for discussion. 6

No equivalent soil described at Merced River. 

morphological evidence that lateral water flow is common 

in the horizons above the dense claypans. It is possible that 

leaching and eluviation extends nearly to the surface in 

these soils that have their argillic B horizons also very near 

the surface. In other words, these A horizons may be more 

like E (albic) horizons than A horizons in terms of dominant 

processes. If this is the case, we should not expect them to 

lie with the other soils in an ascending sequence of horizon 

indices. The horizon indices of A horizons of the lower 

member of the Riverbank and lower member of the Laguna 

continue in ascending sequence (fig. 10). The indices are 

large in these A horizons as a result of the development of 

rubification and structure, in addition to the properties 

melanization and pH that control the younger A horizons. 

The very red color and strong structure in the A horizons of 

the soils of the lower member of the Laguna may be a 

predictable result of extreme soil development. It is possible, however, that these A horizons formed in material that 

was once part of the B horizon due to the complex history 

of soil development, burial, exhumation, and renewal of 

soil development on the lower member of the Laguna 

Formation. 
The profile indices of the chronosequence describe a 

smooth, concave-upward curve when they are graphed 

versus the log of soil age (fig. llA) and a linear curve on a 

log-log plot (fig. liB). The soils formed on Holocene 

alluvium, and on the Modesto, Riverbank, and Laguna 

Formations can be distinguished from one another at the 90 

percent confidence level, calculated from the profile indices 

of the replicate soils on each formational member (fig. 

llA). The soils formed on different members of the same 

formation cannot be distinguished from one another using 

the profile index because the confidence intervals of the 

indices overlap. 

Our inability to distinguish differences in soil development at this level may be due to several factors. First, there 

could be errors in our age assignments; second, the soils 

could truly be indistinguishable due to the influence of other 

soil-forming factors, or due to variations in the rates of soil 

development with time that we do not understand, and 

third, the soil development index could itself incorrectly 

portray or bias our measurements of soil development. 

Sampling of additional replicate profiles presumably would 

narrow the confidence intervals for each soil. Lessening 

en 

a: 

w 

1-

w 

~ 

i= 

z 

w 

() 

~ 

z 

2 

a: 

0 

J: 

-J 

5 

en 

IJ.. 

0 

i= 

a.. 

w 

0 

0.2 0.3 0.4 0.5 0.6 0.7 

HORIZON INDEX 

Figure 10. Composite depth plot showing soil development quantified by average values of horizon indices of 

replicate profiles calculated at 10-cm intervals for soils 

formed in Holocene alluvium (H), upper (UM) and lower 

(LM) members of the Modesto Formation, upper (UR) and 

lower (LR) members of the Riverbank Formation and lower 

member of the Laguna Formation (LL). Profile numbers are 

prefixed HON-. See figure 6 for locations of soil profiles 

(1-22). 

the effect of within-member variation could serve to 

strengthen the soil correlations and also to test the ability of 

the profile index to resolve smaller differences in soil 

development. 

The data in the profile index-age plots (fig. llA, B) 

have a step-and-riser appearance. The two members of the 

Modesto Formation are not greatly different and form one 

step, the two members of the Riverbank Formation form 

another step, and there is a riser or apparent jump in soil 

development between the formations. Changing assumed 

soil ages does nothing to potentially improve the separability of the soils in the index, although it should change the fit 

of the points to the regression line. 

Soils of the upper members of both the Modesto and 

Riverbank Formations appear to be more strongly developed than would be predicted for their ages. The Lagunaage soil could cause this if it is less strongly developed than 

it should be for its age (fig. llB). Given the complex 

history of this soil and the fact that it was exhumed by 

erosion, our age estimate may be in error, or the soil may be 

less strongly developed than this age would predict due to 

the effect of erosion during exhumation. 

The greater than predicted degree of development of 

upper member soils of the Modesto and Riverbank Formations may be caused by nonconstancy of the parent material 

or topographic factors. Both sets of upper member soils 

have formed in silt loam parent materials, in contrast to the 

coarser parent materials of the corresponding sets of lower 

member soils. Soil development in finer materials can be 

expected to be more rapid than in coarser materials because 

smaller mineral particles are more reactive and create soil 

aggregates that have greater water holding capacity. In 

addition, the soils of the upper member of the Riverbank 

were sampled at the base of a slope that descends from a 

terrace of the lower member because it was the best 

available site. Lateral flow of extra water into these soils 

from higher on the slope may have enhanced soil development. The soils on the upper member have skeletans 

(bleached sand and silt grains on ped faces) and other 

features of exaggerated leaching or ponding in the A and 

BA horizons, and have clay-textured Bt horizons. The 

profile indices of the upper and lower members of the 

Riverbank Formation are nearly identical at 102 and 108 

index-em, respectively. By this measure, the two sets of 

soils are indistinguishable. The soils of the upper member 

are as strongly or even more strongly developed than those 

of the lower member in terms of elemental depletion in the 

silt fractions (as shown below) and clay formed in the soil 

profile (Busacca, 1982). Although we believe that the 

topographic factor has contributed to the similarity of the 

soils developed on the two members of the Riverbank 

Formation, Harden (1982a, b) reported that the soils on 

upper and middle members of the Riverbank at the Merced 

River (correlated to our upper and lower members) also are 

nearly identical in development. Harden speculated that soil 

development reaches a temporary plateau in the age range 

late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G53 
of the Riverbank Formation before continuing in older soils 

(J. W. Harden, oral commun., 1984). Without sampling 

additional sites on the upper member in places away from 

the terrace footslopes, we cannot test Harden's hypothesis. 

The soil development index itself may in some applications 

incorrectly portray soil development. For example, because 

horizon thickness .is integrated into the various indices, 

failing to describe a soil to an adequate depth, or describing 

similar soils to different depths, may significantly underestimate or incorrectly estimate soil development. Busacca 

( 1982) reported that when replicate profiles of a chronosequence member had been described to different depths, as 

might commonly occur for Holocene soils, the profile 

indices were widely different unless the calculations were 

corrected to similar depths. Harden and Taylor (1983) 

suggested that the influence of soil thickness can be partly 

eliminated if the property index or profile index is divided 

by the total depth of soil description. They called this the 

weighted mean profile or property index. 

The influence of soil thickness on the profile index can 

be seen by comparing figure 11A and 11 C. The profile index 

versus the log of soil age is strongly concave upward, while 

the weighted mean profile index versus the log of soil age is 

very nearly linear. The interaction of increasing soil thickness with increasing property development clearly leads to 

the strong upward curvature of the profile index (fig. 11A), 

and removing the effect of thickness gives a more appropriate assessment of the increase in soil properties alone 

with soil age (fig. llC). Other differences appear as well. 

The step-and-riser appearance of the plot of Modesto and 

Riverbank soils is less pronounced when weighted means 

are used. In the case of the Riverbank Formation, the soils 

on the upper member were described to greater depths than 

soils on the lower member and the weighted means partially 

compensate for this. Finally, in the transformation to 

weighted mean values (fig. llC), some of the replicate 

profiles appear to be outliers. The two circled points 

represent the coarse sandy profiles on the lower member of 

the Modesto. They are considerably less developed than is 

the soil of the same age formed in silt loam parent material. 

The weighted mean seems to emphasize the effect of parent 

material texture on soil development. The two points 

enclosed in a square represent soils formed on the lower 

member of the Riverbank Formation. These two soils, 

sampled from one trench, have an average profile index of 

100 index-em, compared to an average of 113 index-em for 

the other two, sampled from a second trench. This difference, which is emphasized in the weighted mean estimate, 

suggests that there may be significant differences between 

the two sampling sites in site-specific variables such as 

erosion or parent texture. 

The profile index of soils from the Honcut Creek 

chronosequence can be compared to the profile indices of 

the soils from the terraces of the Merced River 200 km to 

the south (table 10). Although the mineralogy and climate 

G54 Soil Chronosequences in the Western United States 

of the two sites are somewhat different, the profile indices 

for equivalent stratigraphic units compare well, if discrimination of formations is the objective. If soils that are 

300 I I I 

A 

250 L/ -

~ 200- I uti/ - 0 

~ 

w 150 - ..J 

u:: 

0 

a: 1001- a. 

LM ~LA 501-

~ 

2-..UM I -

H 

0 -:t: I I 

1000 I I 

B 

Ly 

LL.X 1001-

UR ~I ow LM~I - ~0 H/I LA J:~ 

t::w a:..J 

c(LL. 

CJO 

oa: 10 /I - ..JQ. 

I I 

0.5 

c I 

0.41- LA LL 

Zx UR: - <w 

wo LM : (I) 

~z 0.3- - oww UM .... ...~ 

0.2- 2-: @ J:U:: - CJO H -a: 

~a. 0.1- 2-= . -

0.00 I I I I 

103 104 105 106 107 

SOIL AGE, IN YEARS 

Figure 11. Age trend of soil development showing profile 

indices versus soil age. Bars are limits of 90-percent 

confidence intervals for replicate soils of each geologic 

unit (abbreviations same as in fig. 10). A, Soil age versus 

profile index. Each point represents one replicate soil 

except where numbers are shown because points are too 

close to plot separately. B, Logarithm of soil age versus 

logarithm of profile index. Each point is the mean of the 

replicate soils of that geologic unit. C, Soil age versus 

weighted mean profile index. Each point represents one 

replicate soil except where numbers are shown because 

points are too close to plot separately. Points in square 

and circle are lless strongly developed soils formed in 

coarse-textured alluvium of lower members of Riverbank 

and Modesto Formations, respectively; see text for discussion. 
thought to be correlated between the two areas have greatly 

different profile indices, the difference may be due to errors 

in correlation and must be investigated further. Differences 

between the two sites in the profile index of soils within 

members of formations may be due to unaccounted-for 

differences in climate, vegetation, parent material grain size 

and mineralogy, or even the depths to which the profile 

index was calculated. 

Mineralogy of the Clay Fraction 

The clay mineral assemblage in fresh stream sediment 

from Honcut Creek and in the parent material of older soils 

is diverse, and consists of vermiculite, kaolinite, smectite, 

mica, chlorite, and chloritized interlayer clays. This suite of 

minerals is progressively simplified with increasing soil 

age. Unstable clay minerals are transformed or dissolved 

and new, stable minerals are formed. The total quantity of 

clay in the A horizons does not appear to increase significantly with time, whereas the clay content of B horizons 

increases greatly due to translocation and neoformation 

(formation in place). For example, B horizons in Modesto 

age soils have 15 to 25 percent clay, depending on parent 

material texture, and B horizons of the soils of the lower 

member of the Laguna have up to 54 percent clay. 

We have plotted the progressive change in abundance 

of three of the principal clay minerals with soil age: 

smectite, kaolinite, and vermiculite (fig. 12A). These 

graphs are qualitative because they were determined by 

changes in peak heights on X-ray diffractograms, nevertheless, they portray the changes very clearly. Chlorite, mica,chloritized interlayer clays, and smectite are all progressively lost from A and B horizons with time. Vermiculite in 

the fine clay of A and B horizons is not present in young 

soils, reaches maximum abundance in soils of the lower 

member of the Modesto Formation and upper member of 

the Riverbank Formation, and then is not detected in the 

older soils (fig. 12A, C). Kittrick (1973) determined that 

vermiculite in soils is a fast-forming but unstable intermediate in the weathering of micas. We may be seeing in the 

soils of Honcut Creek the rapid transformation of fine-clay 

sized mica (probably biotite) to vermiculite in 10 to 40 ka, 

and the subsequent slow dissolution of the unstable vermiculite. It is the dominant coarse clay mineral in stream 

sediments and in the A and B horizons of soils up to those 

of Riverbank age. It then declines in abundance to trace 

amounts in soils of the lower member of the Laguna (fig. 

128, D). Vermiculite probably exists in the coarse-clay 

fraction of stream sediment due to pre-weathering of mica 

in soils of the sediment source areas. Vermiculite dominates 

the coarse-clay fraction in soils of the chronosequence until 

all of the parent mica has been transformed into vermiculite, 

and thereafter its abundance declines as it dissolves. 

Kaolinite is found in moderate to abundant amounts in 

the stream sediment and in A and B horizons of the young 

soils. It increases in abundance with increasing soil age and 

becomes the dominant clay mineral in both coarse- and 

fine-clay fractions of A and B horizons in the soils of the 

lower member of the Laguna. Because the absolute clay 

content in the B horizons increases with soil age to about 54 

percent in these soils, we conclude that a considerable 

amount of new kaolinite has been formed in these soils over 

time. The weathering scheme displayed by the clay minerals in the soils of Honcut Creek is one of desilication, in 

Dominant 

Abundant 

Moderate 

Trace 

Not 

detected 

Dominant 

Abundant 

Moderate w 

u 

z 

<( Trace 0 

z 

::'l 

m 

<( Not 

...J detected <( 

a: 

w 

~ Dominant 

> :S Abundant 

u 

Moderate 

Trace 

Abundant 

Moderate 

Not 

detectedo 

H 

A 

• Smectite 

e Kaolin 

• Vermiculite 

D 

101 102 103 10' 105 106 107 

SOIL AGE, IN YEARS 

Figure 12. Relative abundance of clay minerals determined 

by X-ray diffraction versus soil age (abbreviations same as 

in fig. 10). A, Fine-clay fraction (<0.2tJ.m) of A horizons. 8, 

Coarse-clay fraction (0.2-2.0 tJ.m) of A horizons. C, Fineclay fraction of B horizons. D, Coarse-clay fraction of B 

horizons. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G55 
Table 11. Relative enrichment and depletion of elements in the fine-silt fraction (2-20 t-tm) of A 

horizons of the chronosequence soils 

Geologic Na20 MgO Al 20 3 Si02 K20 CaO Ti02 Fe20 3 Zr 

Unit 

Holocene alluvium 1

1.00 0.98 0.97 1.03 1.05 1.01 0.88 0.97 0.92 

Modesto Formation 

Upper member 1.00 .79 1.03 1.01 1.07 1.05 1.06 .98 1.00 

Lower member .86 .82 .93 1.06 1.01 .96 .98 .86 1.07 

Riverbank Formation 

Upper member .73 .15 .89 1.17 1.45 .74 1.23 .72 1.83 

Lower member .60 .26 .93 1.08 1.53 .79 1.20 .78 1.57 

Laguna Formation 

Lower member .12 .14 .91 1.20 1.81 .22 1.23 .73 2.05 

'Calculated as ratio of element in A horizon to that element in C or BC horizon 

which there is a progressive shift from 2: 1 to 1: 1 layer 

silicate clays and oxide clays with soil age. 

Elemental Composition of Silt-Size Fractions 

The sand and silt fractions of most soils are dominated 

by primary aluminosilicate minerals. Because most primary 

minerals are unstable at earth surface conditions, they are 

reactants in the weathering scheme of the soil and they 

supply elements from which secondary aluminosilicate 

clays and oxide clays are formed. The dissolution of 

primary minerals also releases a substantial part of the 

soluble fraction of elements that are lost completely from 

the soil by leaching. The vertical gradients of temperature, 

moisture, and biological activity in the soil create vertical 

gradients of mineral weathering. The stabilities of the 

common primary minerals vary greatly at the earth's surface, as demonstrated long ago by Goldich (1938), Reiche 

(1950), and others. Elements that are abundant in weatherable minerals are released at higher rates than elements that 

are abundant in weathering-resistant minerals. As soil 

development proceeds, some elements and minerals become depleted relative to others in the soil's framework, 

and a hierarchy of weathering is created. 

We analyzed the elemental composition of the fine- and 

coarse-silt fractions (2-20 JJ.m and 20-50 JJ.m, respectively) 

using energy-dispersive X-ray fluorescence (XRF) spectroscopy to examine the changes in these reactive size fractions 

as a function of soil age. We analyzed only one of the 

replicate soil profiles from each member of the chronosequence (supp. table 6) because of time and budgetary 

constraints. We also analyzed the silt-plus-clay fraction 

(<50 JJ.m) of selected A, B, and C horizons from each 

member of the chronosequence (supp. tables 5, 7), but we 

do not discuss these data here. 

Four major elements, Si, K, Ti, and Zr, become 

enriched in the silt fractions of A and B horizons with 

increasing soil age, whereas five major elements become 

depleted (table 11). The enrichment of Si, K, Ti, and Zr is 

G56 Soil Chronosequences in the Western United States 

relative, not absolute, and results from the fact that these 

elements occur in minerals that resist weathering. The 

weathering-resistant minerals are progressively concentrated with increasing soil age as other more weatherable 

minerals are destroyed. 

The relative enrichment of Si in silt fractions with 

increasing soil age is not due to silicon-bearing minerals 

being absolutely stable to weathering. Quartz dominates the 

fate of silicon because of its moderately high resistance to 

weathering and its abundance in these soils. It acts as a 

reservoir of Si. Silicon is lost from the silt fractions in an 

absolute sense during pedogenesis, as confirmed by Si/Zr 

ratios of silts in soil horizons (table 12). Absolute losses of 

Si occur because of the dissolution of feldspars, ferromagnesian minerals, and quartz. 

Titanium and potassium also become enriched in a 

relative sense in the silt fractions of A and B horizons with 

increasing soil age (table 11), although they too are lost 

from the silt when measured against Zr as a stable element 

(table 12). The loss of titanium from weathering of sphene 

and rutile is important to note in these soils (the Ti/Zr ratios 

in the soils of the lower member of the Laguna show more 

than 40 percent loss of Ti) because Ti has been used as a 

stable element in stable index element studies, although 

some researchers have found that Ti may be mobilized or 

lost during pedogenesis (Sudom and St. Arnaud, 1971; 

Evans and Adams, 1975; Smeck and Wilding, 1981). The 

relative concentration of K in the silt fraction is unexpected 

because the most probable source of K is biotite and 

possibly K-feldspar. Ratios of K to Zr in fine silt of the A, 

B, and C horizons of the soil of the lower member of the 

Laguna (table 12) indicate that only about 15 percent of the 

original K has been lost relative to Zr in 1.6 million years of 

soil development. 

When element loss or gain from the silt fractions is 

judged by examining the ratios of one element to another, 

zirconium is found to be the most stable element of the 

18 elements in the original analysis group. This is shown for 

eight major elements in the soil of the lower member of the 
Table 12. Ratios of elements to zirconium (X10,000) in fine-silt fraction (2-20 J.Lm) of selected horizons of 

soil formed on lower member of Laguna Formation (HON-21) 

Horizon Na20/Zr MgO/Zr AI20/Zr 

A 24.4 29.0 674 

Btl 8.9 27.3 660 

Bt4 0 22.2 889 

3BC 61.1 50.3 1471 

c 250.0 427.0 1498 

Laguna in table 12. The ratios of these eight elements to Zr 

are uniformly smaller in all A and B horizons than in the C 

horizon, indicating net losses in the upper horizons. This 

pattern of element loss in upper horizons is also found in the 

soils of the Riverbank Formation; it is expressed .for some 

elements and some horizons of the soils of the Modesto 

Formation; and element loss is not discernible over the 

noise related to stratification in the Holocene soil. 

Some elements such as Na, Mg, and Ca have been 

almost totally depleted from the silt fractions of the 

Riverbank- and Laguna-age soils. For example, the Btl and 

Bt4 horizons of the Laguna-age soil have Na/Zr ratios of 8. 9 

and 0.0 compared to a ratio of 250 in the C horizon (table 

12). Large losses of the alkali and alkaline earth cations are 

presumably linked to the high weatherability of the ferromagnesian minerals and Na- and Ca-feldspars. 

Zirconium is the most highly enriched element in the 

silt fractions with increasing soil age as a result of greater 

losses of all other elements relative to Zr. Some Zr also 

must be lost from the silt fraction during mineral weathering, but we have no way to measure this. Concentration 

factors for Zr (ratio of average Zr concentration in uppermost three horizons to average Zr concentration in lowermost three horizons) are about 1 in the Holocene soil and 

soil of the upper member of the Modesto, 1.1 in the soil of 

the lower member of the Modesto, about 1.6 in the soils of 

the Riverbank Formation, and about 2.1 and 3.1 in the soil 

of the lower member of the Laguna (table 13). 

Simple plots or regressions of the relative change in 

elemental concentrations or in elemental ratios with soil age 

are useful in examining the marked changes in the silt 

fractions. They are difficult to use, however, in a quantitative analysis because of stratification of parent materials 

within profiles, and because of differences in parent material composition between chronosequence members. For 

example, changes in the relative concentration of K orCa 

that might have resulted from soil development are hard to 

interpret because the parent material content of K and Ca 

varies by as much as a factor of 2 between soils (table 8). 

Some of the changes in element concentrations with soil age 

are striking in spite of this problem. For example, Mg has 

been far more extensively lost from the silt fractions of the 

soils of the Riverbank Formation than has Na (table 11). 

Even from these qualitative changes, we can begin to 

interpret the dynamics of weathering of different primary 

minerals. 

SiOpr K20/Zr CaO/Zr TiOpr Fe20jZr 

2337 57.6 41.2 56.1 307 

2339 57.2 13.3 55.4 275 

2460 59.5 5.7 58.3 371 

3008 64.7 58.7 60.5 786 

4073 67.2 355.0 94.5 855 

The principal effect of soil age does dominate the 

secondary effects of parent material heterogeneity for some 

simple expressions of elemental content. For example, Si 

increases systematically in silt fractions of surface horizons 

with increasing soil age due to the very complete weathering losses of other elements (fig. 13). This pattern is 

similar to those for Ti, Zr, and K, which also become 

enriched in surface horizons, although it is more systematic 

than these others. The regularity of the age trend of 

increasing Si content is interrupted by the high value of the 

upper member of the Riverbank Formation. Once again the 

soil of the upper member appears to be more strongly 

developed than that of the lower member, and we again 

must speculate about the added influences of parent material 

or topographic factors. Our ability to interpret these kinds of 

plots is hampered because we do not have analyses of the 

replicate soils for each chronosequence member as we did 

in the case of the soil development index. 

The element zirconium and the mineral zircon have 

been used previously as stable indices by which changes in 

other elements or minerals can be gauged (for example, 

Barshad, 1964; Drees and Wilding, 1978; Smeck and 

Wilding, 1981; Harden, 1987). Age trends of elements 

compared to Zr are systematic for the Honcut Creek soils. 

This is especially true of the ratio Fe/Zr in the fine silt 

fraction of surface horizons (fig. 14). This age trend is one 

of the clearest derived from a simple elemental ratio,. and 

we think that the reason is that Fe/Zr ratio is less affected by 

stratification of particle-size than is any other elemental 

ratio or particle-size ratio, and the fine silt is less affected by 

stratification than is the coarse silt (table 6). We believe that 

the changes in this ratio with soil age reflect dominantly 

pedogenesis and not parent material heterogeneity. 

Because of the problems encountered in interpreting 

simple element abundances or ratios, we calculated losses 

of elements from the silt fractions by using Zr as a stable 

index. The differences in parent material composition 

between soils dictated that any calculation of change within 

a soil would have to be based on, or normalized to, the 

initial composition of that soil, not on an average parent 

material composition for all soils. The most simple and 

direct calculation of change in elemental composition is: 

Percent remaining 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G57 
where El is the element of interest; R is the stable or 

resistant component, Zr in our case; h is the horizon in 

which the loss is being calculated; and pm is the parent 

material; and percent remaining is the percentage of the 

original content of an element remaining in a soil horizon. 

A similar calculation of percent loss was first used by 

Merrill ( 1921) and has also been used by Harden ( 1982b; 

1987). We used Zr as the stable component because all 

Table 13. Concentration ratios for zircon (average concentration in upper three horizons/average concentrations in 

lower three horizons) in fine- and coarse-silt fraction of 

chronosequence soils 

Geologic Fine silt Coarse silt 

unit (2-20 J.Un) (20-50 J.Un) 

Holocene alluvium .96 11.00 

Modesto Formation 

Upper member .99 .90 

Lower member 1.08 1.10 

Riverbank Formation 

Upper member 1.78 2 1.63 

Lower member 1.48 2 1.58 

Laguna Formation 

Lower member 3 2.08 l3.11 

1

2C horizon only was used in denominator because stratification 

strongly affects 'b concentration in two lowest horizons; see table 8 

and text for discussion. 2

A denominator value of 260 ppm 'b was used because stratification strongly affects 'b concentration in deep horizons; 260 ppm is 

concentration of 'b in fresh stream sediment on Honcut Creek. 3Lowest horizon only was used in denominator because 'b concentrations of next higher horizons are strongly affected by element 

loss. 

80 

..... 

m 10 

0 

a: 

w 

a.. 

~ 

..... - 60 

z 

UJ 

..... 

z 

0 

0 

6" 50 

U5 

104 105 

SOIL AGE, IN YEARS 

Figure 13. Si02 in coarse-silt fraction (20-50 J.Lm) of surface 

horizons versus soil age; r

2 for linear regression is 0.84 

(abbreviations as in fig. 10). 

G58 Soil Chronosequences in the Western United States 

other elements that we analyzed decreased in A and 

B horizons with soil age when compared to Zr. The assumption in this equation is that the initial distribution of Zr and 

the element of interest was uniform throughout the soil 

profile. Our analysis of the stratification in Holocene soils 

and soils of the Modesto Formation above indicates that this 

assumption is more reasonable for the elemental distribution 

in the fine silt than in the coarse silt. We do not assume in 

this equation that the composition of the parent materials is 

uniform between chronosequence soils, because each soil is 

compared only to its own parent material. We used the 

average elemental concentrations in deep BC or C horizons 

(table 8) as parent material in these calculations. This 

method proved valuable in assessing rates of element loss 

from the soils. The calculated data on percentage of the 

original content of an element remaining can be considered 

as depth functions of elemental loss within profiles and as 

comparisons of loss in A orB horizons with soil age, and 

can be used to compare relative rates of loss of different 

elements. 

Holocene soils and soils of the upper member of the 

Modesto provide a check on the method because changes 

due to soil development are minimal. For example, consider 

the calculations of "percentage remaining" for eight elements in the fine silts of the Holocene soil (table 14). For 

AI, Si, Ca, Ti, and Fe, the values range from 92 to 106 

percent and cluster around 100 percent as we would expect 

in an undeveloped soil. Sodium, magnesium, and potassium show more serious effects of stratification. The 

average of the percentage-remaining values for six horizons 

and eight elements in table 14 is 99.7 percent. Iron displays 

values very close to 100 percent for all horizons of the 

Holocene soil (table 14), and as we have found previously, 

it appears to be one of the best elements to use in profile 

reconstructions with Zr. A sedimentological finingupward pattern in the Holocene and other soils affects Zr in 

particular, and leads to a subtle depth trend in the fine silt in 

0 

e 

)( 

N 6 

~ 

0 

Q)N 

!:S 

u. 

0 4 

0 

~ a: 

2~----~------~------~------~------_j 

102 103 104 105 106 

SOIL AGE, IN YEARS 

Figure 14. Ratio of Fe20 3 in percent to Zr in ppm x 100 in 

fine-silt fraction (2-20 J.Lm) of surface horizons versus soil 

age; ~for linear regression is 0.89 (abbreviations as in fig. 

10). 
Table 14. Effect of stratification on the calculation of percentage of original content of elements remaining in the 

fine-silt fraction (2-20 IJ.m) of a Holocene soil using Zr as a stable index 

[If stratification did not affect the index calculation, all values would theoretically be 1 00] 

Basal 

Horizon depth Na2 0 MgO Al 20 3 

(em) 

c 17 103 111 100 

2A 32 95 98 101 

2AC 49 117 103 103 

2C 86 93 95 101 

3C1 113 103 99 98 

3C2 147 88 92 96 

which percentage-remaining values tend to be larger than 

100 percent in surface horizons and less than 100 percent in 

deeper horizons. The trend is more pronounced for some 

elements than others, and is a serious problem for reconstructions of some elements in the coarse silt. It can be 

detected in depth plots because its trend is opposite that 

expected for changes in composition caused by mineral 

weathering and soil development. 

Calculations of percentage of the original content of 

elements remaining using Zr as a stable index confirm that 

all elements that we analyzed in both silt fractions are 

progressively depleted in A and B horizons with increasing 

soil age (tables 15, 16). Different elements behave differently over the course of soil development and are depleted 

to different extents over the 1.6 million years of soil 

development. 

Titanium, potassium, and of course zirconium have .. the 

smallest percentage losses of the elements in tables 15 and 

16. Potassium is very puzzling in its persistence in the silt 

fractions. Surface horizons of the soils of the lower member 

of the Laguna retain 84 percent of the original K in the fine 

silt (table 15) and 57 percent in the coarse silt (table 16). 

Biotite and possibly small amounts of K-feldspar are the 

most likely source of K, and both of these minerals would 

be expected to undergo more severe dissolution in 1.6 

million years. The retention of K in primary mineral 

fractions has also been documented by Harden ( 1982b) for 

soils of the Merced River area that contain abundant 

K-feldspar and muscovite. Weathering losses of Ti, like K, 

are greater in the coarse silt than fine silt; about 48 percent 

of the original Ti remains in the coarse silt (table 16), about 

58 percent in the fine silt (table 15). Ti is depleted to a depth 

of more than 4 m in the soil of the lower member of the 

Laguna. The extent and depth of Ti loss relative to Zr 

clearly indicates that Ti is mobile in this weathering 

environment and is unsuitable as a stable index element. 

The differences in the pattern of loss of Ti with soil age 

in the coarse versus the fine silt suggest further that two 

different Ti-bearing minerals with different solubilities may 

dominate, one in the fine fraction, another in the coarse. 

Silicon, aluminum, and iron have weathering losses 

that are intermediate in extent between the relatively stable 

Percent remaining 

Si02 K2 0 CaO Ti02 Fe2 0 3 

101 111 104 104 102 

102 105 101 97 100 

106 101 103 97 100 

100 98 101 96 101 

97 93 97 100 101 

92 92 92 102 95 

Zr, Ti, and K, and the very unstable Mg, Ca, and Na. The 

sequential loss of Fe and AI from soil horizons with soil 

age can be seen in depth plots of element loss in which all 6 

chronosequence soils are overlaid (fig. 15A, B). 

Holocene soils and soils of the upper member of the 

Modesto do not show any loss of AI that can be detected 

over the influence of stratification, but the fine-silt fraction 

of the 40-ka soil of the lower member of the Modesto has 

lost about 10 percent of its AI (fig. 15A). About 25-50 

percent of the AI has been weathered from the fine silt in the 

upper 1.5 m of the two Riverbank soils; again the upper 

member is more strongly weathered than the lower member. 

As much as 54 percent of the AI in the fine silt and 83 

percent in the coarse silt have been weathered from the 

upper 2 m of the 1.6-Ma soil of the lower member of the 

Laguna Formation (tables 15 and 16). 

The great depth of depletion of elements such as Mg 

and Ca (fig. 15C, D) in the soil of the lower member of the 

Laguna could lead to the conclusion that this soil formed 

under a much wetter, more deeply leaching climatic regime 

in the late Pliocene than that experienced by any of the 

younger soils. This assumption is challenged by the depletion patterns of AI and Fe, which are very similar in depth· 

and extent of loss to patterns for these elements in the 

younger soils. Surprisingly, between depths of 3 and 5 min 

the soil of the lower member of the Laguna, AI and Fe in the 

fine silt actually reach about 125 and 116 percent of original 

content in the parent material. Either stratification has 

caused a major error in the profile reconstructions or there 

has been an actual enrichment of these elements in the 

fine-silt fraction. This part of the profile coincides with a 

plinthite-like zone that has red and white reticulate mottling, and we initially concluded than Fe and AI hydrous 

oxides had crystallized into silt-sized particles at this depth. 

A pilot study using X-ray diffraction and scanning electron 

microscopy so far has failed to support this hypothesis, and 

so its cause is still not known. 

The overall pattern of Fe loss from fine silt is similar to 

that of AI. Note that the depth plots for Fe and AI in the 

Holocene soil and soil of the upper member of the Modesto 

(fig. 15A, B) indicate that stratification is not a major 

problem for reconstructions based on these elements. The 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G59 
Table 15. Percentage of original content of elements remaining in the fine-silt fraction (2-20 1-Lm), calculated 

using Zr as a stable index 

[Values are averages of the upper three horizons] 

Geologic unit Percent remaining 

Na20 MgO Al 20 3 Si02 K20 CaO Ti02 Fe20 3 

Holocene alluvium 105 104 101 103 106 103 100 101 

Modesto Formation 

Upper member 92 80 101 101 105 107 106 99 

Lower member 87 84 89 93 100 83 95 88 

Riverbank Formation 

Upper member 38 9 52 66 77 38 71 41 

Lower member 42 14 62 70 110 56 78 49 

Laguna Formation 

Lower member 9 7 46 52 84 10 58 36 

Table 16. Percentage of original content of elements remaining in the coarse-silt fraction (20-50 1-Lm), calculated 

using Zr as a stable index 

[Values are averages of the upper three horizons] 

Geologic unit 

Na20 MgO Al 20 3 

Holocene alluvium 103 99 99 

Modesto Formation 

Upper member 109 108 107 

Lower member 95 86 91 

Riverbank Formation 

Upper member 51 75 7 

Lower member 50 10 60 

Laguna Formation 

Lower member 7 41 7 

increase in Fe content in the middle horizons of the 10-ka 

soil of the upper member of the Modesto may actually be 

from secondary Fe oxide coatings precipitated on mineral 

grains in the cambic B horizon of this soil. Loss of a few 

percent of Fe seems clear in the soil of the lower member of 

the Modesto, and depletion continues through the 1.6 

million years of soil development. 

Sodium, magnesium, and calcium are rapidly and 

extensively depleted from the chronosequence soils because 

they are bound in the highly weatherable ferromagnesian 

and Na-Ca feldspar minerals. The "reverse trend" in depth 

plots caused by fining upward, and the effect of stratification, can be seen for Mg and Cain the Holocene soil (fig. 

15C, D). Magnesium is the most rapidly depleted of the 

three elements: substantial Mg appears to have been lost 

from fine silt of the 10-ka soil of the upper member of the 

Modesto (fig. 15C, table 15), whereas no loss of Ca is 

evident in the same soil (fig. 15D). Within 130,000 to 

250,000 years, Mg-bearing minerals have been virtually 

eliminated from fine silt in the upper 1.5 m of the soils of 

the Riverbank Formation. Calcium and sodium are far less 

G60 Soil Chronosequences in the Western United States 

Percent remaining 

Si02 K29 CaO Ti02 Fe20 3 

100 100 98 94 96 

110 109 117 114 105 

95 91 94 98 93 

75 80 50 52 46 

73 84 60 54 55 

44 57 8 48 22 

depleted from these same soils (fig. 15D, tables 15 and 16). 

Calcium, sodium, and magnesium are virtually absent in the 

fine silt of the upper 4 m of the soil on the lower member of 

the Laguna Formation. 

Profile reconstructions in the coarse-silt fraction are 

beset by problems of stratification, which obscure the age 

trends to a greater degree. Some elements appear to behave 

differently in the two fractions, and these differences may 

result from the complexity of the size changes that particles 

undergo as they dissolve or fracture with soil age, or from 

the possibility that an element is bound principally in one 

mineral in one size fraction and in another mineral in the 

other fraction. 

The depth of total weathering increases systematically 

with soil age (table 9), but each element has its own 

depth-depletion trend (fig. 15A-D). The lithologic discontinuities in the soils of the Riverbank have acted as barriers 

to deeper elemental losses, and this complicates the results. 

Weathering intensities appear to be greatest from about 

40 to 150 em, and less at the surface (see, for example, fig. 

15D). The horizons just beneath the soil surface may remain 
200 

400 

~ 200 w 

1-

w 

~ 

.i= 

z 

w 

(.) 400 

~ 

~ f ~1200~- ~ --~----~--~~--~r 50 75 100 ...J Or-:-....---.-------.------r--...----,-~---, 

6 

C/) 

LL 

0 

w 

~ 200 co 

~ 

~ 

1- fu 400 

0 

r 

25 50 75 100 

FRACTION OF ORIGINAL CONTENT 

REMAINING, IN PERCENT 

moist more of each year than those at the surface and 

become more weathered, but we cannot eliminate the 

possibility that eolian dust has rejuvenated the mineral suite 

in the surfaces. 

Linear regressions of percentage of an element remaining versus the log of soil age yields results that are 

comparable to those based on simple relative enrichment or 

depletion. The trends of element depletion for the major 

elements in the fine silt are all significant at between the 5 

and 1 percent levels, with coefficients of multiple determination (r2

) of between 0. 78 and 0.86. The slopes of the 

linear regressions with respect to the log of soil age for.Si, 

Fe, Na, and Mg are in the order of increasing rate of 

element release from the silt fractions of the Honcut soils 

(fig. 16A-D). For Si and Fe, elements that are less strongly 

influenced by parent material heterogeneity, and for Na, 

element loss with soil age is very systematic. However, in 

each of these plots (fig. 16A-D), the soil of the upper 

member of the Riverbank flaws this pattern and adds further 

suspicion that topographic and parent material factors have 

strongly influenced its development. 

The lack of elemental analyses for the replicate profiles 

of each member is the greatest limitation to the use of this 

data in soil correlation. Without the replicates, we cannot 

estimate confidence intervals of element loss for each 

member. Analysis of a limited number of replicate soil 

horizons during XRF methods testing suggested that elemental chemistry would be about as useful as the soil 

development index in discriminating geologic formations 

and members by the properties of their soils. 

The soil age trends for Si, Fe, Na, and Mg and others 

not shown suggest that a particular element may be well 

suited in the correlation of soils in one particular age range 

and not well suited in other ranges. For example, because of 

the very large decrease in Mg between 40 and 130 ka, this 

element may work well to discriminate soils on the Modesto 

Formation from those on the Riverbank (fig. 16D), whereas 

Na may be most useful to discriminate soils of the Riverbank from those of the Laguna Formation (fig. 16C). 

We examined the element release calculations and 

determined a mobility or release series for elements in the 

silt fractions. We used the average element release values 

for the Riverbank Formation (tables 15 and 16) because 

depletion is nearly total for several elements in the 1.6 Ma 

Figure 15. Fraction of original content of elemental oxides 

remaining (calculated relative to Zr) in fine-silt fraction 

(2-20 IJ.m) versus soil depth (abbreviations as in fig. 10). 

A, Al 20 3 ; 8, Fe20 3 ; C, MgO; D, CaO. Results over 100 

percent due to stratification of parent alluvium and possibly pedogenic accumulation (see text for discussion). 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G61 
lower Laguna soil. The mobility series are different for the 

two silt fractions. In the fine silt (2-20 J.Lm): 

Mg ~ Na>Fe = Ca>Al>Si>Ti>K>Zr 

In the coarse silt (20-50 J.Lm): 

Mg~ Na>Fe = Ti>Al>Si>K>Zr 

The series also is somewhat changed if other time 

ranges are. used. Polynov's (1937) series is Ca>Na>Mg 

>K>Si>Al>Fe; however, it is based on the ratio of an 

element in ground water to that element in unweathered 

bedrock. It is a measure of the elements that escape entirely 

from the soil by deep leaching. Our series is based only on 

rate of release from primary minerals in soils and does not 

take into account the later fate in the soil of those elements, 

such as Fe, AI, and Si, that are strongly complexed in clay 

minerals that form concurrent with weathering of primary 

minerals in the soil profile. 

Summary of Trends in Soil Development 

and Their Use in Soil Correlation 

Soils formed on relatively uneroded alluvial terraces at 

Honcut Creek change systematically with increasing soil 

age. Differences in soil development here can be used, with 

some caution, to correlate deposits from site to site in the 

local area, and to test age correlations with soils and 

deposits in other areas. Soils on the different deposits can be 

recognized in the field by key differences in morphology 

with time: (1) reddening of color hue in B-horizons, (2) 

increasing depth to fresh parent material, (3) increasing 

distinctiveness of soil horizons, and (4) sequential development of A horizons, cambic B, weak argillic B, strong 

argillic B, and extremely strong and thick argillic B 

horizons. The soil development index of Harden (1982a) 

integrates many of these properties in a numerical index that 

can be used in the field. As we gathered stratigraphic and 

geomorphic evidence of the formations and members, we 

were able to use the distinctive characteristics of the soils 

and the soil-landscape patterns to map the distribution of 

each formation in detail. We used soil morphology, which 

is the basis for defining soil series, to distinguish between 

members of a formation in the field (table 2) even when we 

later found that some quantitative laboratory measures of 

soil development, such as elemental depletion, failed to do 

so. For example, we found that the Kimball and Yokohl 

series soils are consistently associated with the upper 

member of the Riverbank Formation, and the Kimball-deep 

variant with the lower member. 

At this time, the soil development index of Harden 

( 1982a) is the most useful single measure of soil development that we have tested for distinguishing soils formed on 

G62 Soil Chronosequences in the Western United States 

deposits of different ages. This is in part because it was 

designed specifically for comparisons of the degree of soil 

development versus age. Using the index, we have been 

20 

0 

B 

..... 100 

z 

w 

(.) 80 a: 

w 

a.. 

~ 60 

ci 

z 40 z 

<( 

~ 20 w 

a: 

..... 0 z 

w 

..... c ~ 100 

(.) 

....J 

ct 80 

z 

a 

a: 60 

0 

u.. 

0 40 

z 

0 

i= 20 

(.) 

ct 

a: 

u.. 0 

D 

100 

80 

60 

40 

20 

103 104 105 106 107 

SOIL AGE, IN YEARS 

Figure 16. Fraction of original content of elemental oxides 

remaining (calculated relative to Zr) in fine-silt fraction 

(2-20 J.Lm) of surface horizons versus soil age (abbreviations as in fig. 10). A, Si02 , r for linear regression is 0.84. 

8, Fe2 0 3 , r

2 is 0.78. C, Na2 0 3 , r is 0.86. D, MgO, r is 0.79. 

Results over 100 percent due to stratification of parent 

alluvium. 
able to distinguish between the soils developed on the four 

major alluvial deposits (Holocene, Modesto, Riverbank, 

and Laguna); however, we are not able to distinguish 

statistically significant differences in soil development between members of the same formation. We believe that this 

is the result of uncontrolled variation in other soil-forming 

factors, principally parent material grain size and mineralogy, and topography, and not of major errors in our 

stratigraphic or age interpretations. Weighted mean profile 

indices, which factor out soil depth differences, appear to 

improve the ability of the soil development index to 

differentiate small differences in soil development. The 

small area of the Honcut Creek flood plain and terraces 

would make it difficult to find new sampling sites at which 

parent material and topographic factors would be more 

closely r:natched, in order to further test the development 

index. 

We offer a comparison of the profile index calculated 

for soils from Honcut Creek with those calculated by 

Harden (1982b) for soils on the terraces of the Merced River 

200 km 'to the south (table 10). Profile indices of soils in the 

two areas match reasonably well when discrimination of 

formations is the objective. This can be considered to be a 

test of age and stratigraphic correlations between these two 

areas. The differences in profile index values between 

correlative members of formations in the two areas may be 

due to differences between sites in climate, vegetation, and 

parent material grain size and mineralogy. The differences 

may also be significant with respect to soil age assignments 

and may call certain correlations into question. 

Changes in clay mineralogy with soil age reveal much 

about the developmental history of these soils but are of 

limited use in correlation studies because they are at best 

qualitative measures of the minerals present, and because 

minerals in the clay fraction are, by their nature, both 

reactants in and products of the pedogenic process. 

We believe that depletion of elements from the weathering of primary minerals in silt:-sized fractions is a fruitful 

area of research, both for what we can learn about mineral 

weathering and soil formation and for its potential in soil 

correlation. The relationships with soil age tend to be 

simple and unidirectional because the silt (and sand) fractions are reactants in the weathering process and the scheme 

is one of loss over time. 

X-ray fluorescence analysis of the silt fractions documented systematic changes in soil development over time. 

Si, Ti, K, and Zr tend to become enriched in silt fractions 

with increasing soil age because of very complete weathering removal of Ca, Mg, Na, and to a lesser extent Fe and 

AI. Zr is the most stable element in the silt fractions by a 

factor of up to 3 in the near-surface horizons of the soil of 

the lower member of the Laguna .. Calculations of change in 

elemental composition with respect to Zr used as a stable 

index are successful, and the changes can be evaluated 

withdepth in each soil, or with soil age in selected horizons 

of all soils. 

Trends of element depletion with soil age are systematic for those elements and elemental ratios in which parent 

material heterogeneity does not cause major interference. 

Silicon and iron, and calculations of change in these 

elements with respect to Zr yield among the best results. 

Lack of X-ray fluorescence data from our replicate soil 

profiles made it impossible for us to test soil correlations 

statistically, but we believe that if replicate data were 

available, elemental chemistry would discriminate geologic 

formations and members as well as or better than the soil 

development index. 

Profile morphology, clay mineralogy, and elemental 

chemistry reveal similar, systematic changes in the chronosequence of soils at Honcut Creek. This indicates to us 

that the major pedogenic processes acting under the climates, parent materials, and vegetation at Honcut Creek are 

progressive over the 1.6-million year estimated span of soil 

development rather than cyclic or intermittent. Progressive 

changes are significant because they provide the best 

indices of soil and landscape age, and because they provide 

information about the pedogenic processes that drive soil 

development over long periods of time. 

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SUPPLEMENTARY TABLES 1-11; 

SUPPLEMENTARY FIGURE 1 
EXPLANATION 

SOIL TEXTURE 

1s loamy sand sil silt loam scl sandy clay loam sg slightly gravelly 

sl sandy loam sicl silty clay loam sc sandy clay gr gravelly 

1 loam sic silty clay vg very gravelly 

+ heavy cl clay loam ext. gr extremely gravelly 

light c clay 

SOIL CONSISTENCE 

Dry Moist Wet 

lo loose lo loose so non sticky po nonplastic 

so soft vfr very friable ss slightly sticky ps slightly plastic 

sh slightly hard fr friable s sticky p plastic 

h hard fi firm VS very sticky vp very plastic 

vh very hard vfi very firm 

SOIL STRUCTURE 

Grade Size Type 

1 weak vf very fine m massive sbk subangular blocky 

2 moderate f fine sg single grain abk angular blocky 

3 strong m medium g granular pr prismatic 

c coarse cr crumb __... parting to 

vc very coarse pl platy 

ROOTS 

Abundance Size Orientation 

1 few vf veryfme h horizontal 

2 common v fine v vertical 

3 many m medium r random 

c coarse onpf on ped faces 

PORES 

Abundance Size Shape Orientation 

1 few vf very fine t tubular r random 

2 common f fine interstitial h horizontal 

3 many m medium v vertical 

c coarse c continuous 

CLAY FILMS 

Frequency Thickness Location 

v1 very few vn very thin pf ped faces 

1 few n thin po pore linings (usually tubular pores) 

2 common mk moderately thick br bridging grains 

3 many k thick pc coating pebbles or gravels 

4 continuous 

HORIZON BOUNDARIES 

a abrupt 

c clear 

g gradual 

d diffuse 

s smooth w wavy 

irregular 

G68 Soil Chronosequences in the Western United States 
Supplementary table 1, part 1. Site locations 

[Soil-profile sites were originally prefixed HOS-] 

Site and soil- Geologic Soil-profile site locations, 

profile number unit Mount Diablo Base and Meridian 

HON-1 Holocene alluvium SW~NE~ sec. 30, T. 17 N., R. 4 E. 

HON-2 SW~NW~ sec. 31, T. 17 N., R. 4 E. 

HON-3 SW~NW~ sec. 31, T. 17 N., R. 4 E. 

HON-4 SW~NE~ sec. 31, T. 17 N., R. 4 E. 

HON-5 Upper member, NE~SW~NE~ sec. 31, T. 17 N., R. 4 E. 

HON-6 Modesto Formation NE~SW~NE~ sec. 31, T. 17 N., R. 4 E. 

HON-7 SE~SE~SE~ sec. 22, T. 17 N., R. 4 E. 

HON-8 SE~SE~SE~ sec. 22, T. 17 N., R. 4 E. 

HON-9 Lower member, 150m W. of Ctr. sec. 24, T. 17 N., R. 3 E. 

HON-10 Modesto Formation 150m W. of Ctr. sec. 24, T. 17 N., R. 3 E. 

HON-11 SE~SW~SW~ sec. 13, T. 17 N., R. 3 E. 

HON-13 Upper member, NE~SW~ sec. 16, T. 17 N., R. 4 E. 

HON-14 Riverbank Formation NE~SW~ sec. 16, T. 17 N., R. 4 E. 

HON-17 Lower member, NE~SE~ sec. 16, T. 17 N., R. 4 E. 

HON-18 Riverbank Formation NE~SE~ sec. 16, T. 17 N., R. 4 E. 

HON-19 SE~SE~SE~ sec. 17, T. 17 N., R. 4 E. 

HON-20 SE~SE~SE~ sec. 17, T. 17 N., R. 4 E. 

HON-21 Exhumed lower member, NW~ sec. 23, T. 17 N., R. 4 E. 

HON-22 Laguna Formation NW~ sec. 23, T. 17 N., R. 4 E. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G69 
Supplementary table 1, part 2. Field descriptions 

Basal Consistence 

Profile Sample depth Lower Moist Dry 

no. no. Horizon (em) boundary color to lor Texture Dry Moist Wet 

Holocene alluvium, 

HON-1 A 12 a,s 10YR3/3 10YRS/4 sh fr ss,po 

2 2A1 16 a,s 10YR3/2.5 10YRS/3 sil h fr ss,po 

3 2A2 25 c,s 10YR3/3 10YRS/3 sh fr ss,ps 

4 2AC 49 c,s 7.SYR4/3 10YRS/4 sh fr ss,ps 

5 2C 85 c,s 7.SYR4/3 10YRS/4 sh fr ss,po 

6 3C1 95 a,s 7.SYR4/4 10YRS/4 sl so vfr so,po 

3C2 122 7.SYR4/4 10YRS/4 sl sh vfr so,po 

HON-2 10 A1 4 a,s 10YR3/2.5 10YRS/3 sil sh fr ss,ps 

11 A2 32 a,w 10YR3/2.5 10YRS/4 sil-l sh fr ss,ps 

12 c 61 c,s 10YR3/3 10YRS/4 so vfr so,po 

13 2C 92 c,s 10YR4/4 10YRS/4 1-sl vfr ss,po 

14 3C 103 10YR3/3 lOYRS/5 vfr ss,ps 

HON-3 16 A1 4 a,s 10YR3/3 10YRS/3 sil sh vfr ss,ps 

17 A2 16 g,s 10YR3/3 10YRS/4 sil sh fr ss,ps 

18 AC 31 a,w 10YR3/3 10YRS/4 sil sh fr ss,ps 

19 c 54 a,w 10YR4/3 lOYRS.S/4 so vfr so,po 

20 2C 78 10YR4/3 10YR6/4 so vfr ss, ps 

HON-4 21 c 17 a·,s 10YR4/3 10YR6/3 sl so vfr so,po 

22 2A 32 c,s 10YR3/3 10YRS/3 sh vfr ss,ps 

23 2AC 49 c,s 10YR3/3 10YRS/4 sil so vfr ss,ps 

24 2C 86 g,s 10YR3.5/3 10YRS/4 vfr ss,ps 

25 3C1 113 g,s 10YR4/3 lOYRS/4 sl vfr so,po 

26 3C2 147 10YR4/3 lOYRS/4 sl vfr so,po 

G70 Soil Chronosequences in the Western United States 
Assumed parent material 

Consistence 

Structure Roots Pores Clay films pH Texture Dry Moist Wet 

0.6 ka 

I f,mgr lf,2m 2vf, f i 6.5 lo lo so,po 2m crt lf,gr 2vf,lf,lm 2vf i 6.6 sil so vfr ss,po 2vf crt I f,mgr lvf, f,m 2vf, f i 6.5 lo lo so,po lf,m crt m lvf,f,m 1 vf i 6.6 lo lo so,po 2f,m crt m lvf,m lf,2m crt 6.8 lo lo so,po 

m->sg lvf ,m If crt 6.7 sl lo lo so,po 

m->sg lvf, f ,m,c If crt 7.0 sl lo lo so,po 

2f,mgr lf, 2vf ,m 2vf, f i 5.6 sil so vfr ss,po 2vf,f,m crt m->lf,msbk lf,m,2vf lvf,fcvt 6.2 sil so vfr ss,po 

m->sg If ,2vf 1 vf, f cvt 6.8 lo lo so,po 

m->sg lf,2vf 1vf,f crt 7.1 lo lo so,po 

m 1vf,f 1vf,f crt 7.2 lo lo so,po 

2f ,mgr 2f,m,3vf 1vf,f cvt 5.9 sil so vfr ss,po 2vf,fi 

lf,mgr 2vf, f ,m 1vf,m, 2f cvt 5.8 sil so vfr ss,po 1vf,f i 

1m,csbk 2vf,lf 1vf,f,m crt 6.1 sil so vfr ss,po 

m->sg lvf, 1f lvf,f crt 7.1 lo lo so,po 

m-+sg lvf,f lvf,f crt 7.0 lo lo so,po 

sg lf,2vf,m r 1vf,lm,2f crt 6.5 sl lo lo so,po 

2f,mgr 1f,1m,2vf r 3vf ri 6.9 lo lo so,po 1m,c,2vf,f crt m-+1m,csbk 1m,c,2vf,f h lvf,f crt 6.6 sil so vfr ss,po 

m 1f,m,c,2vf h 1vf,f,m crt 6.7 lo lo so,po 

m 1vf,f,2m,c 1m,2vf,f crt 6.8 s1 lo lo so,po 

m-+sg 2v f, f, m , c , h lf,lm,2vf crt 6.7 sl lo lo so,po 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G71 
Supplementary table 1, part 2. Field descriptions-Continued 

Profile 

no. 

HON-5 

HON-6 

HON-7 

HON-8 

HON-9 

Sample 

no. 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

51 

52 

53 

54 

55 

56 

57 

Horizon 

Ap1 

Ap2 

BA 

Bw1 

Bw2 

BCl 

BC2 

Ap1 

Ap2 

BA 

Bw1 

Bw2 

BC1 

BC2 

Ap1 

Ap2 

BA 

Bw1 

Bw2 

BC 

2BC 

Apl 

Ap2 

BA 

Bw1 

Bw2 

BC1 

BC2 

none Apl 

assigned 

Ap2 

BAtl 

BAt2 

2Bqkml 

2Bqkm2 

2BCqm 

3BCt 

3C 

Basal 

depth 

(em) 

13 

23 

54 

88 

102 

141 

180 

10 

22 

43 

91 

118 

151 

184 

8 

30 

54 

88 

118 

180 

230 

34 

57 

90 

126 

191 

240 

16 

25 

42 

80 

99 

113 

137 

153 

198 

G72 Soil Chronosequences in the Western United States 

Lower 

boundary 

a,w 

c,w 

c,s 

c,s 

c,s 

g,s 

a,w 

c,w 

c,s 

c,s 

c,s 

g,s 

c,s 

c,s 

g,s 

g,s 

g,s 

c,s 

a,s 

c,s 

C,S 

c,w 

g,s 

g,s 

c,s 

g,s 

a,s 

a,w 

c,w 

c,w 

c,w 

c,w 

c,w 

Moist 

color 

7 .5YR3/2 

7.5YR3/3 

7.5YR3/3 

7.5YR3/3 

7.5YR3/4 

7 .5YR4/4 

7.5YR4/4 

7 .5YR3/2 

7 .5YR3/2 

7 .5YR3/2 

7 .5YR3/3 

7.5YR3/3 

7.5YR4/4 

7.5YR4/4 

7.5YR3/3 

7 .5YR3/3 

Dry 

color 

7.5YR5/4 

7. 5YR5/4 

7.5YR4/3 

7 .5YR4/3 

7 .5YR5/4 

7.5YR5/4, 

5/6 

7 .5YR5/4 

7.5YR5/4 

7 .5YR5/4 

7 .5YR4/3 

7 .5YR4/3 

7.5YR5/4 

7.5YR5/4 

7 .5YR5/4 

7/5YR5/4 

7 .5YR5/4 

7.5YR3/2.5 7.5YR4/4 

7.5YR3/4 

7.5YR3/4 

7 .5YR4/4 

10YR4/3 

7 .5YR3/3 

7.5YR3/3 

7 .5YR3/3 

7.5YR3/4 

7.5YR3/4 

7.5YR4/4 

7.5YR4/3 

10YR3/3 

10YR3/3 

10YR3/3 

10YR4/3 

10YR4/3 

10YR4/3 

10YR4/3 

7.5YR4/6 

7 .5YR5/5 

7 .5YR5 .5/5 

10YR5/4 

7 .5YR5/4 

7 .5YR5/4 

7.5YR4/4 

7 .5YR4/6 

7 .5YR5/5 

7 .5YR5/5 

7.5YR6/4 

10YR6/2.5 

10YR6/3 

10YR5.5/3 

10YR5/4 

10YR5/3 

10YR5/3 

10YR5/3 

10YR4/3 10YR5/3 

10YR6/2.5 10YR7/2 

Consistence 

Texture Dry Moist Wet 

Modesto Formation, 

sil vh fi ss,ps 

sil h fi ss,ps 

sil+ h fi ss ,ps 

sil h fr ss,ps 

sil vh fr ss,ps 

sil-l h fr ss,ps 

sil-l h fr ss,ps 

sil vh fi ss,ps 

sil h fr ss,ps 

sil h fi ss,ps 

h fi ss,ps 

fr ss,po 

h fr ss,po 

h fr ss,po 

vh vfr ss ,ps 

VII vfr ss,ps 

sil-l h fr ss,ps 

sh vfr ss,ps 

sh fr ss,ps 

sh fr ss,ps 

sicl- sh fr ss,ps 

vh fr so,ps 

vh fr so,ps 

h fr ss,ps 

h fr ss,ps 

h fi ss,ps 

sh fi ss,ps 

1-sil sh fr ss,ps 

Modesto Formation, 

1-sil h fr ss,ps 

1-sil h fr ss,ps 

h fr ss,ps 

vh fi vs,vp 

scl- cemented---------------

scl- cemented---------------

fsl weakly cemented--------

h fr ss,ps 

h fr ss,ps 
Structure Roots 

upper member, 10 ka 

m-+-cloddy 

2f ,mgr 

m-+lcsbk 

2m,cabk 

2mabk 

2mabk 

lmabk 

m(cloddy) 

2m,cabk 

2mabk 

2mabk 

lmabk 

cloddy 

m,compact 

2:n,cabk 60% 

2f,mgr 40% 

2m,cabk 

2m,cabk 

lf ,mabk 

cloddy, 

compacted 

massive 

compacted 

lmsbk 

2m,csbk 80% 

2f,mgr 20% 

2m,cabk 

2m,cabk 

lm,cabk 

lf ,2vf 

lf ,2vf 

lvf,f,m 

2vf,f 

lf,2vf 

lvf,f 

lvf ,f 

lf ,2vf 

2vf,f 

1vf,f,m 

2vf,3f,m 

2vf ,lf 

2vf,f 

lvf 

3vf 

3vf 

3vf 

3vf 

2vf 

1vf 

lvf 

3vf 

3vf 

3vf 

3vf on pf 

lower member, 40 ka 

cloddy 

3m,cabk 

3m,cabk 

3m,cabk 

2m,csbk 

m-+lmsbk 

m 

3vf,2f,lm 

2vf,f,1m 

2vf,1f,lm 

2vf 2f, 

lm on pf 

no roots 

no roots 

no roots 

no roots 

no roots 

Miscellaneous 

mn sheen on pf 

mn sheen on pf 

Fe mott 

7 .5YR5/6 

Fe mott: fli 

Mn shot 

Fe mott: c2i 

Mn stains: fli 

Mn shot: c2i 

Mn stains on pf 

Mn stains on pf 

Fe mott: 

10YR6/6 D 

Pores 

2vf,f,m crt 

lvf,f crt 

2vf i 

Clay films 

1m,2vf,f crt 2n pf 

1n po 

lm,2vf,f crt 3n pf 

3n po 

2vf, 2f crt 3vn pf 

lf,2vf crt 

1vf,f crt 

2vf,f,m crt 

2vf,f,m crt 

3vn po 

2vn pf 

2vn po 

2vn pf 

2vn po 

lm,2vf,f crt 2n pf 

2n po 

2vf,f,m crt 3n pf 

3n po 

2vf, f ,m crt 3vn pf 

3vn po 

2vf, f ,m crt 2vn pf 

2vn po 

1 vf, f crt 2vn pf 

2vn po 

2vf crt 

2vf crt 

pH 

6.2 

6.3 

6.7 

7 .o 

7.1 

7.2 

7.3 

6.2 

6.4 

6.6 

7.0 

7.0 

7.2 

7.4 

5.6 

5. 7 

2f,m,3vf crt 2vn br 6.(, 

2vn po 

3vf,f,m,co 2vn br 7.0 

crt 2vn po, 1 vn ,pf 

2m,3vf,f crt 2vn po 7.2 

3vf,f,m crt 

2vf,f,m crt 

lm,2f,3vf 

crt 

2f,m,3vf crt 

2c,3vf,f,m 

crt 

2f,m,c,3vf 

crt 

2vf, f ,m,c 

crt 

2vf,f,m crt 

lvf,f cvt 

2vf,1f,m crt 

3vf,2f,lm 

crt 

2vf,lf,1m 

crt 

2vf,f crt 

2vf,f crt 

3vf, 2f ,m crt 

3vf ,3f ,2m 

crt 

3vf,f,2m crt 

2vn br 

lvn br 

lvn po 

2vn br 

2vn po 

3vn br 

3vn po 

2vn br 

3vn po 

lvn br 

lvn po 

7.3 

7.2 

5.6 

5.8 

6.3 

6.8 

7.1 

7.3 

7.3 

7.0 

v1 vn po 7.2 

vl vn br 

3npo,1npf 7.4 

vl mk br 

3mkpf,lkpf 7.5 

3mkpo 

2n br,lmk br 8.2 

in waves 

2n br ,lmk br 8. 2 

in waves 

ln br,lmk br in 8.2 

waves; 3mk po 

ln,mk br 8.2 

3mk po 

3n,mk po 8.2 

Assumed parent material 

Consistence 

Texture Dry Moist Wet 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

1o lo so,po 

lo lo so,po 

lo lo so,po 

lo 1o so,po 

1o lo so,po 

lo lo so,po 

sil-l so vfr ss,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

sicl- so vfr ss,po 

1o lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

1o lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

fsl lo lo so,po 

fsl lo lo so,po 

fsl lo lo so,po 

lo lo so,po 

lo lo so,po 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G73 
Supplementary table 1, part 2. Field descriptions-Continued 

Profile 

no. 

HON-10 

HON-11 

HON-13 

HON-14 

Sample 

no. 

59 

60 

61 

62 

63 

64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74 

75 

76 1 

77 

78 

79 

80 

81 

82 

83 

84 

85 

86 

87 

88 1 

89 

90 

91 

92 

93 

94 

Horizon 

Ap 

BA 

Btl 

Bt2 

BC 

c 

2C 

Ap 

BA 

Btl 

Bt2 

BC 

c 

2C 

Ap 

BA 

BAtl 

BAt2 

Btl 

Bt2 

Bt3 

BCt 

2BCtl 

2BCt2 

2BCt3 

2CB 

Ap 

BA 

BAtl 

BAt2 

Btl 

Bt2 

2BCtl 

2BCt2 

2BCt3 

2CB 

Basal 

depth 

(em) 

22 

40 

86 

132 

150 

205 

225 

18 

45 

94 

125 

145 

179 

220 

24 

33 

so 

62 

86 

102 

123 

157 

208 

245 

266 

301 

28 

39 

59 

76 

111 

126 

150 

200 

260 

320 

G74 Soil Chronosequences in the Western United States 

Lower 

boundary 

c,w 

g,s 

g,s 

c ,s 

c,s 

a,w 

a,w 

g,s 

g,s 

c,w-+-i 

g,w-+-i 

a,w 

a,s 

c ,s 

c,s 

c,s 

c .s 

c,s 

c,s 

g,w 

g,w 

g,w 

d,w 

a,s 

c,s 

c,s 

c,s 

c,w 

c,w 

g,w 

g,w 

d,w 

Moist 

color 

7 .SYR3/2 

7.SYR3/3 

7.SYR4/3 

Dry 

color 

7. SYRS/2 

7.SYRS/3.5 

7. SYRS/4 

Texture 

sgsl 

sgsl 

sgsl 

5-7.5YR3/4 7.SYRS/S sgsl 

7.SYR4/3 

7. SYR4/3 

2. SY4/3 

7. SYR3/2 

7.SYR3/3 

7. SYR4/3 

7.SYR3/4 

7 .SYR4/4 

7 .SYR4/4 

2.SYS/4 

7. SYR4/S 

SYR4/4 

SYR4/4 

SYR4/S 

5YR4/6 

SYR4/6 

SYR4/S 

7.SYR4/6 

SYRS/6, 

SYR3/4 

SYR4/6, 

SYR3/4 

SYR4/6, 

SYR3/4 

SYR4/S 

7.SYR4/4 

7 .SYR4/4 

SYR4/S 

SYR4/S 

SYR4/6 

SYR4/6 

7 .SYRS/6 

cfSYR4/4 

7. SYRS/6 

cfSYR4/4 

SYR4/6 

SYR4/6 

7 .SYRS/4 sgs1 

7. S-10YRS/ 4 sgsl 

10YR6/4 

7. SYRS/2 

7.SYRS/3.5 

7.SYRS/4 

7.SYR4/4 

7. 5YR5/5 

7.SYRS/S 

10YR6/4 

7. SYR6/6 

7. SYRS/6 

SYRS/5 

SYRS/5 

SYRS/6 

SYRS/6 

5-7 .SYRS/6 

7 .SYR6/6 

fsl 

sgsl 

sgsl 

sgsl 

sgsl 

sgsl 

sgsl 

sil 

sil 

sil-l 

sil-l 

1+ 

csic 

sicsicl 

7. SYR6/6 peds scl 

SYR4/ 4 skins 

7. SYR6/6 peds cl 

7. SYR4/ 4 skins 

7.SYRS/6peds scl7 .SYR4/4 skins 

SYRS/6 s1 

7. SYR6/6 

7 .SYRS/6 

SYRS/5 

SYRS/5 

SYRS/6 

SYRS/5 

7. SYR6/6 

SY:R4/6 

7 .SYR6/6 

SYR4/4 

5, 7 .SYR 

5/6,6/6 

SYRS/6,6/6 

sil 

sil 

sil 

cl 

sic 

cl 

cl 

c1-sicl 

clsclConsistence 

Dry Moist Wet 

Modesto Formation, 

sh fr ss,po 

vh fi so,po 

h fr ss,ps 

h fr ss,ps 

sh vfr ss,po 

so vfr so,po 

sh vfr so,po 

sh fr ss,po 

vh fi ss,ps 

sh vfr ss,ps 

h fi s,p 

sh fr ss,po 

so vfr so,po 

h fr ss,po 

Riverbank Formation, 

sh vfr ss,po 

sh vfr ss,ps 

sh fr ss,ps 

h fr s,p 

vh vfi vs,vp 

vh fi vs,vp 

vh fi s,vp 

h fi ss,p 

h fr ss,ps 

h fr ss,ps 

sh fr ss,ps 

sh fr so,ps 

sh vfr ss,po 

sh vfr ss,ps 

h fr ss,p 

h fr s,p 

vh vfi vs,vp 

vh vfi s,vp 

h fr s,p 

h fr ss,ps 

sh fr ss,ps 

sh fr so,ps 
Structure Roots 

lower member, 40 ka 

lm,csbk+ 

lf,mgr 

m, compacted 

2m,csbk 

2m,cabk 

2m,csbk 

m+sg 

m 

lm,csbk+ 

2f ,mgr 

m,compacted 

2m,csbk 

2m,cabk 

2m,csbk 

m+sg 

m,strat 'd 

3vf,f,m 

root m 

lm,2f,3vf 

2f,3vf 

2f ,2vf 

1f,2vf 

1f,2vf 

lf,2vf 

lc,2m,3vf,f 

2m,3vf,f 

2f,m,c,3vf 

2f ,3vf 

2vf,f 

2vf ,f 

2vf,f 

upper member, 130 ka 

cloddy 

m+lfmsbk 

2m,csbk 

2mpr+2cabk 

3m,cpr+ 

3m,cabk 

3m,cabk 

3m,cnbk+ 

2fabk 

3mabk+ 

. 2f,vfnbk 

m+2m,cabk 

m+lm,csbk 

m+1m,csbk 

m+1m,csbk 

m+cloddy 

m+lf ,msbk 

2msbk,abk 

2f,mpr+ 

2m,cabk 

3m,cpr+ 

3m,cabk 

3m,cabk 

3m,cabk+ 

3vf,fabk 

2m,cabk 

m+1m,cabk 

m+1m,csbk 

3vf,f 

2f ,3vf 

2vf,f 

lf ,2vf 

3vf 

1vf 

lvf 

2f ,3vf 

3vf 

3vf 

3vf 

2vf 

1vf 

Miscellaneous 

Fe mott: fli 

10YR6/8 D 

Pores 

3f ,m,c crt 

2vf ,f i 

2c,3f crt 

3vf ,f i 

2vf ,m,3f crt 

3vf ,f i 

2vf,f,m,c 

crt 

3vf,f,m crt 

3vf ,f i 

2f, 3vf crt 

3vf ,f i 

2vf,f crt 

2m,c,3vf,f 

crt; 3vf i 

2m,c,3vf,f 

crt 

3m,c crt 

2vf ,f i 

3vf,f,m,c 

crt 

2m,3vf,f,c 

crt; 2vf ,f i 

2vf,f,lm crt 

3vf, f i 

2vf,f crt 

2m,3vf,f crt 

Clay films pH 

6.8 

6.8 

3n br, 1mk br 6 . 8 

1n po,3n pc 

3mk br, 3mk pc 7. 2 

1n-mk pf, 2n po 

2n br 7.2 

lvn po 

2n br 

3n br,2n pc 

2n po 

3mk br ,lmk pf 

2mk po 

2n br 

7.2 

7.2 

6.6 

7.0 

7.0 

7.1 

7.2 

7.3 

7.3 

5.5 

Mn shot: c2r 2f,m,3vf crt 2vn po 6.3 

Mn shot: c2r 

Mn shot: c2r 

Mn shot: flr 

few Mn shot 

no Mn 

~In shot: clr 

Mn stains on pf 

Mn stains on pf 

Mn stains on pf 

no Mn 

Mn shot: c1r 

3vf,f,m crt 

2vf,f,lm 

crt 

3vf on pf 

lvf into ped 

2vf on pf 

lvf into ped 

2vf on pf 

1vf into ped 

1vf on pf 

lvf into ped 

1f,m,2vf crt 

1f,m,2vf crt 

lf,m,2vf crt 

1vf i 

1f,m,2vf crt 

1m,3vf,f crt 

2n pf 6.5 

2n po 

2mkpf,3npf 6.8 

2mk po,3n po 

4k pf stress 6.8 

cutans 

4k pf stress 6.6 

cutans 

4k pf stress 7.1 

cutans 

4mk pf 7.1 

4mk po 

3mkpf,3mkpo 7.2 

2mk br,2n br 

ln pf in po 7. 1 

1mkpf, 2nbr, 2mkbr 

ln pf, 2mk po 6. 9 

3n br 

1mk po 6. 7 

3n br 

5.6 

Mn shot: clr 1m,c,2f,3vf ln po 6.1 

crt 

Mn shot: c2r 1m,c,2f,3vf 2n pf 6.5 

crt 2n po 

Mn shot: c3r 2f ,3vf crt 3npf,3npo 6.7 

1mk pf, 1mk po 

~In shot: flr 3vf crt 4k pf stress 6.7 

cutans 

Mn stains on pf 2vf crt 4k pf stress 7.0 

cutans 

Mn stains on pf 3vf crt 4kpf,4kpo 7.1 

4mk pf ,4mk po 

Mn stains on pf 1f,2vf crt 2npf,2npo 6.9 

Mn stains on pf lf,2vf crt 

2mkpf, fmkpo, 3mkbr 

1npf,lnpo 6.8 

1mkpf, 1mkpo, 3mkbr 

no Mn lf,2vf crt 1k po,3mk br 6.8 

lvn.pf 

Assumed parent material 

Consistence 

Texture Dry Moist Wet 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sl lo lo so,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

lo lo so,po 

lo lo so,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sl lo lo so,po 

sl lo lo so,po 

s1 lo lo so,po 

sl lo lo so,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

sil so vfr ss,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

sl lo lo so,po 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G75 
Supplementary table 1, part 2. Field descriptions-Continued 

Profile 

no. 

HON-17 

HON-18 

HON-19 

HON-20 

Sample 

no. 

95 

96 

97 

98 

99 

100 

101 

102 

103 

104 

105 

106 

107 

108 

109 

110 

111 

112 

113 

114 

115 1 

116 

117 

118 

119 

:20 

123 

124 

125 

126 

127 1 

128 

129 

130 

Horizon 

Apl 

Ap2 

BA 

Btl 

Bt2 

2BCt 

3BCt 

4BCt 

Apl 

Ap2 

BA 

Btl 

Bt2 

2BCt 

3BCt 

4BCt 

Apl 

Ap2 

BA 

Btl 

Bt2 

Bt3 

BCt 

2BCtl 

2BCt2 

2BCt3 

Apl 

Ap2 

BA 

Btl 

Bt2 

2BCtl 

2BCt2 

2CB 

Basal 

depth 

(em) 

18 

24 

76 

100 

160 

201 

208 

295 

19. 

30 

90 

113 

170 

190 

240 

300 

24 

63 

91 

126 

176 

218 

246 

268 

300 

11 

30 

60 

114 

191 

223 

260 

283 

G76 Soil Chronosequences in the Western United States 

Lower 

boundary 

c,w 

a,w 

g,w 

g,w 

c,w 

g,w 

c,s 

c,w 

a,w 

g,w 

c,w 

g,w 

c,w 

c,s 

c,w 

a,w 

g,w 

c,w 

g,w 

c,w 

c, s 

g,s 

g,s 

c,w 

a,w 

c,w 

c,i 

c,w 

g,s 

g,s 

Moist 

color 

5YR3/4 

5YR3/4 

2.5YR3/4 

2.5YR3/5 

2.5YR3/5 

2. 5YR3/5 

5YR4/5 

2.5YR4/6 

5YR3/4 

5YR3/4 

2.5YR3/5 

2. 5YR3/5 

2.5YR3/6 

2.5YR3/6 

5YR4/6 

2.5YR4/6 

5YR3/4 

5YR3/4 

2.5YR3/5 

2. 5YR3/5 

2.5YR3/6 

2.5YR3/6 

5YR4/6 

5YR4/6 

5YR4/6 

5YR4/6 

SYR3/4 

5YR3/4 

5YR3/5 

2. 5YR3/5 

2 .5YR3/6 

5YR5/6 

5YR4/6 

5YR4/6 

7. 5YR5/6 

Dry 

color Texture 

5-7.5YR5/4 

5YR5/5 

2. 5YR4/4-

5YR4/6 

2. 5YR5/6 

clcl 

2. 5YR5/6 peds cl 

2. 5YR4/6 skins 

2. 5YR5/6 peds scl 

2. 5YR4/6 skins 

5YR5/6 cl5YR5/6 peds vgscl 

2.5YR4/5 skins 

5YR5/4 

5YR5/5 

5YR4/6 

2 .5YR5/6 

2.5YR5/6, 

4/6 

2.5YR5/6, 

4/6 

5YR5/6, 

6/6 

5YR5/5, 

5/6 

5YR5/4 

5YR5/4, 

7 .5YR5/4 

2.5YR4/5 

1+ 

cl 

sicl 

clclvgscl1+ 

2.5YR5/6peds 1+ 

5YR4/4 skins 

2. 5YR5/6 peds cl 

2.5YR4/4 skins 

2.5YR5/6peds cl 

2. 5YR4/ 4 skins 

5YR6/6 peds scl2.5YR4/5 skins 

5YR5/6 sgsl 

5YR6/6 

5YR6/6 

5YR5/4 

SYR5/4 

sgsl 

5YR4/5, 1+ 

5/5 

2.5YR5/6 peds 1+ 

2.5YR4/4 skins 

2.SYRS/6peds cl 

2. SYR4/6 skins 

SYR6/6 peds sgscl5YR5/6 skins 

5YR5/6 peds sgsl+ 

5YR4/ 4 skins 

7.5YR6/6 sl 

Consistence 

Dry Moist Wet 

Riverbank Formation, 

h fr ss,ps 

sh fr ss,ps 

sh fr s,ps 

vh fr s,ps 

vh fi s,ps 

vh fi s,p 

h fi s,ps 

sh fr s,ps 

h fr ss,ps 

sh fr ss,ps 

sh vfr s,ps 

vh fi s,ps 

vh fi vs,p 

vh fi s,p 

h fi s,p 

sh fr ss,po 

sh fr so,po 

h fr so,ps 

sh vfr ss,ps 

sh fr s,p 

h fi s,p 

vh fi s,p 

vh fi ss,ps 

sh fr ss,ps 

sh fr ss,ps 

so vfr so,po 

sh vfr so,po 

h fr so,ps 

so vfr ss,ps 

sh fr ss,p 

vh fi s,p 

h fr ss,p 

sh fr ss,ps 

so vfr so,po 
Structure Roots 

lower member, 250 ka 

cloddy-+lfgr 2c,3vf,f,m 

m-+lsbk 2vf,f,3m 

3vf,f,mcr lm,2vf,f 

30\ 2f ,msbk 

2m,csbk lm,2vf 

20\ fgr 

2fpr-+2m,cabk 1vf ,m 

m-+2mabk lvf 

m-+2mabk lvf 

m-+1m,cabk lvf 

2msbk-+2f ,mer 2f, 3vf 

m-+2m,csbk 2f,m,3vf 

2vf ,mer, lf ,3vf 

10\ 2msbk 

2m,csbk, 2vfi 

30\ 2vf, f ,mer 3m,cpr-+3mabk 2vfi 

m-+2m,cabk lvf 

m-+2m,cabk 

m 

cloddy-+2£ ,mer 3vf, f ,m 

m-+lm,csbk 2m,3vf,f 

2m,csbk-+ 

2f ,mer 

2m,csbk, 

30\ 2fcr 

3m,cpr-+ 

3m,cabk 

3f,m pr 

3f ,mabk 

2mabk 

m-+2mabk 

m-+2msbk 

m-+lmsbk 

cloddy-+ 

2c,vccr 

m-+1m,csbk 

2vf,f,mcr 

2m,csbk 

35\ 2f ,mer 

3m,cpr-+-

3m,cabk 

2cabk 

m-+2cabk 

m-+lmsbk 

2m,3vf,f 

2m,3vf,f 

2vf,f 

lvf,2f 

lf ,2vf 

lf,2vf 

2vf 

3vf,f,m 

3vf,f,m 

2f,m,3vf 

2m,3vf,f 

lm,2vf ,f 

2vf,f 

lvf,f 

Miscellaneous 

Mn stains on pf 

Mn stains on pf, 

in po 

Mn stains on pf, 

in po 

Mn stains on 

gravels 

Mn shot: flr 

Mn stains on pf 

Mn stains on pf 

Mn stains in 

pores 

Mn stains on pf 

and in pores 

Pores Clay films pH 

2c,3vf,f,m 5.7 

2m,3vf crt s. 7 

2c,3vf,f,m 6.1 

2f,3vf,m crt 2mkpf,4npf 6.4 

4n po 

1m,3vf,f crt 3mk pf 6.6 

4k pr 

2m,3vf crt 2kbr,4mkbr 6.8 

lk po 

lm,3vf crt 3k br in 6.9 

waves 

lm, 2vf crt 1k br in waves 6. 8 

2mk br,1k pc 

2m,3vf,f crt 

3vf,f,m i 

2f,m,3vf crt 

2f,m,c,3vf 

crt; 3vf,f i 

2f,m,3vf crt 

lf,2vf crt 

lvf,f crt 

2vf crt 

lvf,f,m crt 

3vf,f i 

3vf,f,m crt 

3vf,f,m crt 

3vf, f i 

3vf,f,m crt 

3vf ,f i 

3vf,f,m crt 

1m,2vf,f crt 

lm,2vf,f crt 

2vf,f crt 

2vf,f crt 

3vf i 

2vf crt 

3v'f i 

3vf ,f i 

3vf,m,2f 

3vf, f i 

3vf,f,m,c crt 

3vf,f i;2m,c, 

3vf,f crt 

2vf,f crt 

2f,3vf crt 

3vf i 

lvf,f,m crt 

3vf i 

lvf crt 

lmk br ,2n po 

3n br 

3mk br, 3mk pf 

lmk po 

4k pf 

4k br 

3mk br,2k br 

in waves 

3mk br ,2k br 

in waves 

3n br,2mk br 

1k pc 

2n br 

5.5 

5.5 

6.1 

6.6 

6.8 

6.9 

6.8 

6.8 

6.3 

6.0 

6.1 

2n br 6.2 

2n pf 

2mk pf 6.6 

3n pf 

2kpf 7.0 

2mk pf 

lk pf 6.9 

3mk pf 

vlmk pf in 7.2 

waves; 3mk br, 3mk pc 

3n br, 2mk br 7 . 1 

3n pc 

ln br 6.9 

1mk pc 

2n br 

3n br 

2n pf 

3mkpf,1kpf 

2n pf 

3mk br, 2mk pf 

in waves 

2n br, 1mk pf, 

2mk pc in waves 

2n br 

6.2 

6.2 

6.3 

6.8 

7.1 

6.8 

6.9 

Asswned parent material 

Consistence 

Texture Dry Moist Wet 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

sl lo 1o so,po 

lo lo so,po 

vgsl lo lo so,po 

lo lo so,po 

lo 1o so,po 

lo lo so,po 

lo lo so,po 

sil so vfr ss,po 

lo lo so,po 

lo lo so,po 

vgsl 1o 1o so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

sgsl lo lo so,po 

sgsl lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

lo lo so,po 

sgs1 lo lo so,po 

sgs1 lo lo so,po 

1s lo lo so,po 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G77 
Supplementary table 1, part 2. Field descriptions-Continued 

Basal Consistence 

Profile Sample depth Lower Moist Dry 

no. no. Horizon (em) boundary color color Texture Dry Moist Wet 

Laguna Formation, 

HON-21 131 A 11 c ,s 2.5YR3/4 SYR4/4 sl+ sh vfr so,po 

132 AB 33 c,w~,i 2.5YR3/4 2.5YR4/4 scl sh fr so,ps 

133 BA 46 a,w-+a, i 2. SYR3/4 2.5YR4/5 sgscl-cl sh fr ss,ps 

134 Btl 71 c,w 2.5YR3/5 2. SYR3/6 sgc fi s,p 

135 Bt2 93 c,w 10R3/5 10R3/6, sgc fi s,p 

4/8 

136 Bt3 119 c,w 10R3/6 10R4/6 sgc h fi s,p 

137 Bt4 148 g,w 10R3/6 10R4/6 sgc h fi s,p 

13B 2Btl 197 g,w 10R3/6 10R4/6, grc sh fr ss ,p 

4/8 

139 2Bt2 274 d,w 2. SYR3/6 2.5YR4/6 grcl sh fr ss,p 

140 2BC 315 d,w 2. SYR3/6 2. SYR4/6 grcl fr ss,po 

141 3BC 473 a, i SYR3/4 SYR4/3 extg fr so,po 

1+ 

142 "C" >1200 7.5YR4/3 7. SYR6/3 s1 sh vfr so,po 

HON-22 143 A 23 c,w 2.5YR3/4 2.5YR4/4 scl- sh fr ss,ps 

144 AB 43 c,w 2.5YR3/5 2. SYR4/5 sgscl sh vfr ss ,ps 

145 BA 59 a,w-t-i 2. SYR3/5 2.5YR4/5 sgc sh fr s,p 

146 Btl 89 c,w 10R3/5 10R3/6 sgc fr s ,p 

147 Bt2 120 c,w 10R3/6 10R3. 5/6 sgc fi s,p 

148 Bt3 154 g,s 10R3/6 10R3/6, sgc fr s,p 

4/6 

149 2Btl 207 g,s 10R3/6 10R3/6, grc 

4/6 sh fr s,p 

150 2Bt2 270 g,w 10R3/6 2. SYR3/6, grc1++ sh fr ss,p 4/6 

151 2BCt 342 g,w 2.5-SYR3/4 2.5YR4/4, vgrcl sh vfr ss,ps 

4/6 

152 3BCtl 445 g,w SYR3/4 SYR3/4 ext gel sh vfr ss,po 

153 3BCt2 505 a,w SYR4/4 SYR4/4 extg+ sh fr ss,po 

154 "C" >1200 SYR4/4 SYR4/6 sl sh vfr so,po SYR4/4 skins 

1

sandy skeletans on ped faces. 

G78 Soil Chronosequences in the Western United States 
Assumed parent material 

Reticulate mottling Consistence 

Structure Roots Pores Clay films Abundance Colors pH Texture Dry Moist Wet 

exhumed lower member, 1, 600 ka 

2csbk .. lf ,mgr lf ,3vf 3vf,f i 6.2 sl lo lo so,po 

2csbk-+2f ,mgr lf,m,3vf 2m,3f crt ln po 6.2 sl lo lo so,po S\ 2f ,mgr 3vf, f i 2m,csbk 2vf,f,lm,c 3f,m crt 3n pf 6.2 sgsl lo lo so,po 3vf, f i 3n po 3m,cnbk lf ,m,c, 2vf 3vf crt 4k pf stress s. 7 sgsl lo lo so,po cutans;4k po lf,mpr-+ lvf,f,m 2vf crt ",4k pc S.3 sgsl lo lo so,po 3m,cnbk 

lmpr-+3m,cnbk lvf,f,m,l 2vf crt S\ faint SYR6/6 D s.o sgsl lo lo so,po subhor. SYR4/4 M lmpr-+3m,cabk 1vf 2vf crt 10\ 7.SYR7/4,7/2 o· 4.9 sgsl lo lo so,po 7 .SYR6/4 M 3m,cabk vlvf lvf crt 4k pf,4k po 20-2S\. as above s.o grsl lo lo so,po 4k pc avg dia em 2m,cabk vlvf 1vf crt 4k pf ,4k po 2S-30\ 7.SYR7/2,7/4,7/6 D S.3 grsl lo lo so,po 2vf i 4k pc 7 .4YR6/2,6/4,6/6 M 2m,fnbk 2vf, f i 3k pf as above as above, plus s. 7 grsl lo lo so,po 3k pc 7/SYRS/4 D, 7/4 M 2f,mabk 3vf,f,m 2k pf >SO\ 7 .SYRS/4 D 6.1 extg sl lo lo so,po 2mk pc 7. SYR6/6 ,6/8 M m .. lcsbk 6.2 sl lo lo so,po 

2csbk 3vf,f 1f,m,2vf i lvn pf? 6.4 sl lo lo so,po burrows lfgr lvn po? lmsbk+ lc,vc,2m,3vf 2m,c,3vf crt lvn pf,lvn po 6. 7 sgsl lo lo so,po lvf,f,mgr 3vf i lvn pc 2msbk lvc,2vf,f,m 2m,c,vc, 3mk pf, 3mk po 6. 7 sgsl lo lo so,po 30% 1 fgr 3vf,f crt 3mk pc lf,mpr .. lf,m,2vf lm,2vf,f crt 4k pf stress cu- 6.9 sgsl lo lo so,po 3f,m,cabk t~s,4kr,o,4kpc 

3m,cnbk 1f,m,2vf 1f,m,2vfcrt occasional S.9 sgsl lo lo so,po faint mottle 3m,cabk lf,m,2vf lf,m,2vf crt 10\ subhor. 7.SYR7/2 D S.4 sgsl lo lo so,po 7 .SYR6/2 M 3m,cabk lvf lvf,f crt 1S-2S\ 7. SYRS/2, 7/2, 7 I 4 

7.SYR6/2,6/4 M 

D S.4 grsl lo lo so,po 

3fabk lvf lvf,f crt 3mk pf, 3mk po 2S\ 7.SYR7/2,7/6 D S.4 grsl lo lo so,po 3mk pc 7.SYR7/2,6/4 M 2m,csbk 2f,m,c i 2k br,2k pc 30-SO\ 7 .SYRS/2 D s.s grsl lo lo so,po 2k po 7.SYR7/2 M lf ,msbk 3f,m,c 2k po,2k pc >SO\ 7.SYR6/8,8/2 D 6.1 extg sl lo lo so,po 2k br 7.SYRS/7,7/2 M lf,msbk 3f,m,c 2mk po, 2mk br >7S\ 7 .SYR7/2,6/4 D 6.0 extg sl lo lo so,po 2kpo, 2kbr, 2mkpc 7.SYR6/2,S/4 M m->lm,csbk 3f,m,c 2n br 6.9 sl lo lo so,po 2mk br 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G79 
Supplementary table 2. Physical properties 

[Analysts: A.J. Busacca, K. Trott, and J.R. Anikju] 

Percentage of <2-mm fraction 

Sample Profile Horizon Basal >2 mm Total vco co m fi+vfi Silt <2-J.Lm <1-J.Lm Bulk 

number number depth sand sand sand sand sand clay clay density 

(em) (g/cm3) 

Holocene alluvium, 0.6 ka 

1 Hon-1 A 12 0.0 40.6 0.2 2.2 3.3 34.8 43.0 16.3 12.6 1.26 

2 Hon-1 2A1 16 0.0 28.9 0.4 1.8 2.4 24.3 54.0 17.1 12.9 1.30 

3 Hon-1 2A2 25 0.0 42.8 0.0 0.6 2.7 39.5 41.0 16.2 12.6 1.34 

4 Hon-1 2AC 49 0.0 40.5 0.1 0.7 2.8 36.9 43.9 15.6 12.8 1.41 

5 Hon-1 2C 85 0.0 48.0 0.2 0.6 1.8 45.4 39.2 12.8 10.3 1.39 

6 Hon-1 3C1 95 0.0 59.4 0.1 1.1 4.3 53.9 30.1 10.5 8.5 1.35 

7 Hon-1 3C2 122 0.0 59.9 0.0 2.0 9.8 48.1 28.2 11.9 9.6 1.50 

8 Hon-1 4C1 140 0.0 66.4 0.5 15.8 19.0 31.1 22.2 11.4 9.3 1.55 

9 Hon-1 4C2 170 0.0 62.3 0.4 16.6 17.0 28.3 24.9 12.8 10.7 1.61 

10 Hon-2 A1 4 0.0 27.2 0.3 0.5 0.3 26.1 52.9 19.9 15.9 1.33 

11 Hon-2 A2 32 0.0 29.5 0.1 ·0.2 0.2 29.0 51.0 19.5 15.9 1.48 

12 Hon-2 c 61 0.0 50.7 0.0 0.1 0.2 50.4 36.1 13.2 10.7 1.33 

13 Hon-2 2C 92 0.0 52.8 0.0 0.1 0.2 52.5 34.2 13.0 10.5 1.30 

14 Hon-2 3C 103 0.0 44.0 0.0 0.0 0.1 43.9 40.2 15.8 12.3 1.29 

15 Hon-2 4C 130 0.0 43.1 3.0 16.7 8.2 15.1 41.0 15.9 12.4 1.48 

16 Hon-3 A1 4 0.0 18.6 0.1 0.2 0.3 18.0 57.7 23.7 18.3 1.16 

17 Hon-3 A2 16 0.0 23.8 0.0 0.0 0.2 23.6 54.4 21.8 16.7 1.39 

18 Hon-3 AC 31 0.0 25.6 0.0 0.0 0.2 25.4 53.1 21.3 16.5 1.51 

19 Hon-3 c 54 0.0 49.6 0.0 0.0 0.2 49.4 37.2 13.2 10.5 1.35 

20 Hon-3 2C 78 0.0 47.9 0.0 0.0 0.2 47.7 37.9 14.2 11.5 1.30 

21 Hon-4 c 17 0.0 59.0 0.0 0.2 1.5 57.4 31.6 9.4 8.0 1.25 

22 Hon-4 2A 32 0.0 37.3 0.1 0.2 0.5 36.5 46.9 15.8 13.0 1.26 

23 Hon-4 2AC 49 0.0 29.4 0.0 1.0 0.4 27.9 53.7 16.9 13.7 1.24 

24 Hon-4 2C 86 0.0 35.8 0.0 0.2 0.8 34.7 49.3 14.9 12.7 1.33 

25 Hon-4 3C1 113 0.0 54.7 0.0 0.1 1.0 53.6 34.5 10.8 9.0 1.35 

26 Hon-4 3C2 147 0.0 64.7 0.0 0.6 5.7 58.4 25.4 9.9 7.8 1.42 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 Ap1 13 0.0 18.7 0.2 0.9 1.4 16.2 58.0 23.3 18.7 1.54 

28 Hon-5 Ap2 23 0.0 18.0 0.3 0.9 1.4 15.4 58.6 23.4 19.0 1.76 

29 Hon-5 BA 54 0.0 18.0 0.2 0.8 1.2 15.8 56.7 25.3 21.0 1.67 

30 Hon-5 Bw1 88 0.0 20.7 0.1 0.8 1.2 18.6 55.4 23.9 19.6 1.69 

31 Hon-5 Bw2 102 0.0 24.8 0.2 0.7 1.3 22.6 52.6 22.6 18.7 1.58 

32 Hon-5 BC1 141 0.0 28.2 0.2 0.8 1.4 25.8 49.4 22.4 18.9 1.77 

33 Hon-5 BC2 180 0.0 27.3 0.0 0.8 1.6 24.9 50.9 21.8 18.2 1.80 

34 Hon-6 Ap1 10 0.0 23.0 0.5 0.9 1.4 20.2 53.6 23.4 17.9 1.57 

35 Hon-6 Ap2 22 0.0 22.5 0.1 0.9 1.4 20.1 54.0 23.5 18.1 1.71 

36 Hon-6 BA 43 0.0 25.4 0.2 0.7 1.3 23.2 50.3 24.3 19.6 1.55 

37 Hon-6 Bw1 91 0.0 31.6 0.6 1.7 2.1 27.2 46.4 22.0 17.5 1.50 

38 Hon-6 Bw2 118 0.0 31.8 0.2 1.7 2.2 27.7 46.9 21.8 17.6 1.72 

39 Hon-6 BC1 157 0.0 27.0 0.1 0.7 1.5 24.7 50.2 22.8 18.7 1.81 

40 Hon-6 BC2 184 0.0 30.2 0.2 1.0 2.2 26.7 48.2 21.6 17.8 1.83 

41 Hon-7 Ap1 8 0.4 34.4 0.8 2.3 2.7 28.6 46.7 18.9 15.2 1.80 

42 Hon-7 Ap2 30 1.0 32.8 1.3 2.4 2.4 26.7 47.7 19.5 15.5 1.80 

G80 Soil Chronosequences in the Western United States 
Supplementary table 2. Physical properties-Continued 

Percentage of <2-mm fraction 

Sample Profile Horizon Basal >2 mm Total vco co m fi+vfi Silt <2-~m <1-~m Bulk 

number number depth sand sand sand sand sand clay clay density 

(em) (glcm3) 

Upper member of the Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 0.0 27.8 0.9 2.9 3.0 21.0 51.4 20.8 16.5 1.57 

44 Hon-7 Bwl 88 0.0 28.7 1.1 3.0 3.0 21.6 48.5 22.8 18.4 1.54 

45 Hon-7 Bw2 118 0.0 32.5 0.8 2.5 3.1 26.1 46.5 21.0 17.6 1.78 

46 Hon-7 BC 180 0.0 31.1 0.5 2.0 3.0 25.6 47.3 21.6 17.8 1.74 

47 Hon-7 2BC 230 0.0 12.0 0.5 0.9 1.0 9.6 60.4 27.6 21.8 1.64 

48 Hon-7 3Cox 290 1.8 42.9 1.4 2.7 1.5 37.3 39.9 17.2 13.9 0.00 

49 Hon-7 4Cox 340 0.7 79.4 7.6 27.4 18.8 25.6 12.8 7.8 6.3 0.00 

50 Hon-7 4Cn 370 0.3 83.3 9.4 35.0 17.4 21.5 11.2 5.5 4.2 0.00 

51 Hon-8 Apl 7 1.1 34.6 0.9 2.6 3.0 28.1 46.5 18.9 15.1 1.72 

52 Hon-8 Ap2 34 2.9 33.4 1.2 2.9 3.1 26.2 47.0 19.6 15.6 1.68 

53 Hon-8 BA 57 0.5 29.8 2.0 3.5 3.3 21.0 47.0 23.2 18.7 1.56 

54 Hon-8 Bwl 90 0.6 31.4 1.6 4.1 3.3 22.4 47.3 21.3 17.4 1.70 

55 Hon-8 Bw2 126 0.0 32.2 1.0 2.9 2.7 25.6 47.3 20.5 16.8 1.73 

56 Hon-8 BCl 191 0.0 19.8 0.3 0.8 1.2 17.5 57.1 23.1 18.9 1.70 

57 Hon-8 BC2 240 0.0 32.4 0.4 1.2 2.4 28.4 48.9 18.7 15.0 1.63 

58 Hon-8 2Cox 390 0.8 88.0 8.7 42.5 20.2 16.6 7.5 4.5 3.4 0.00 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 6.3 59.1 11.1 17.6 8.3 22.1 29.6 11.3 8.0 1.63 

60 Hon-10 BA 40 5.9 61.7 12.5 21.1 9.6 18.6 26.1 12.2 9.1 1.79 

61 Hon-10· Btl 86 6.5 64.6 15.7 22.2 9.4 17.3 24.3 12.1 9.1 1.69 

62 Hon-10 Bt2 132 5.6 59.9 9.8 20.0 9.4 20.7 26.2 13.9 13.0 1.76 

63 Hon-10 BC 150 7.0 68.4 11.4 22.9 12.1 22.0 21.1 10.5 8.3 1.67 

64 Hon-10 c 205 10.5 71.4 12.7 23.0 12.5 23.2 20.2 8.4 6.4 1.62 

65 Hon-10 2C 225 2.9 50.0 3.8 5.2 2.7 38.3 32.5 7.5 5.3 1.43 

66 Hon-11 Ap 18 8.0 55.6 9.2 17.7 8.2 20.5 30.8 13.6 10.0 1.55 

67 Hon-11 BA 45 5.0 62.7 12.0 21.6 9.5 19.6 24.9 12.4 9.3 1.94 

68 Hon-11 Btl 94 6.1 60.9 10.4 20.7 9.4 20.3 25.7 13.4 10.5 1.74 

69 Hon-11 Bt2 125 4.4 56.3 7.4 19.3 8.8 20.8 28.6 15.1 11.9 1.72 

70 Hon-11 BC 145 6.7 64.9 11.8 21.6 10.4 21.1 23.8 11.3 9.0 1.70 

71 Hon-11 c 179 14.3 67.7 14.4 21.6 11.3 20.4 22.3 10.0 8.0 1.66 

72 Hon-11 2C 220 0.0 39.2 0.3 0.8 0.6 37.5 53.2 7.6 5.2 1.48 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 0.0 28.9 2.0 4.3 4.1 18.5 54.6 16.5 11.6 1.50 

74 Hon-13 BA 33 0.0 28.3 2.0 4.0 4.1 18.2 51.8 19.9 14.5 1.77 

75 Hon-13 BAtl 50 0.0 27.6 2.2 4.1 4.2 17.1 49.2 23.2 17.7 1.68 

76 Hon-13 BAt2 62 0.0 37.2 2.9 6.9 7.3 20.1 36.4 26.4 21.4 1.80 

77 Hon-13 Btl 86 0.0 31.3 2.7 5.6 6.9 16.0 25.7 43.0 39.1 1.91 

78 Hon-13 Bt2 102 0.0 14.5 0.7 1.8 2.6 8.14 34.6 50.9 46.4 1.96 

79 Hon-13 Bt3 123 0.0 14.1 0.5 1.3 1.8 10.5 44.1 41.8 35.7 1.93 

80 Hon-13 BCt 157 0.0 13.8 0.0 1.0 1.8 11.0 52.7 33.5 29.9 1.87 

81 Hon-13 2BCtl 208 0.0 46.9 0.2 1.2 4.2 41.3 27.4 25.7 22.7 1.89 

82 Hon-13 2BCt2 245 0.0 56.7 0.2 0.6 7.2 48.7 19.0 24.3 22.0 1.86 

83 Hon-13 2BCt3 266 0.0 61.7 0.0 1.0 8.9 51.8 17.1 21.2 19.4 1.83 

84 Hon-13 2CB 301 0.0 70.7 0.9 8.6 21.4 39.8 11.9 17.4 16.2 1.78 

late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G81 
Supplementary table 2. Physical properties-Continued 

Percentage of <2-mm fraction 

Sample Profile Horizon Basal >2 mm Total vco co m fi+vfi Silt <2-~m <1-~m Bulk 

number number depth sand sand sand sand sand clay clay density 

(em) (g/cm,) 

Upper member of the Riverbank Formation, 130 ka-Continued 

85 Hon-14 Ap 28 0.0 28.8 1.9 4.2 4.2 18.5 55.2 16.0 10.7 1.55 

86 Hon-14 BA 39 0.0 25.8 1.6 4.2 3.8 16.1 52.3 21.9 15.7 1.69 

87 Hon-14 BAtl 59 0.0 25.2 1.6 4.4 4.1 15.1 51.4 23.4 17.7 1.65 

88 Hon-14 BAt2 76 0.0 24.5 1.0 4.2 4.7 14.6 45.1 30.4 22.7 1.76 

89 Hon-14 Btl 111 0.0 12.8 0.9 2.0 1.9 8.0 42.6 44.6 38.7 1.91 

90 Hon-14 Bt2 126 1.0 24.6 1.8 4.6 3.7 15.3 38.5 36.9 32.6 1.95 

91 Hon-14 2BCtl 150 0.0 24.4 0.1 0.6 1.3 22.3 41.6 34.0 30.2 1.93 

92 Hon-14 2BCt2 200 0.0 21.2 0.4 1.1 1.1 18.5 48.7 30.1 26.5 1.77 

93 Hon-14 2BCt3 260 0.0 42.1 0.1 0.8 3.0 38.1 30.5 27.4 24.3 1.73 

94 Hon-14 2CB 320 0.4 57.1 0.7 2.5 7.5 46.4 20.3 22.6 19.6 1.78 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 3.5 42.1 4.4 7.7 5.8 24.2 40.2 17.7 13.0 1.60 

96 Hon-17 Ap2 24 3.4 42.3 4.3 8.5 5.7 23.8 39.9 17.8 13.3 1.64 

97 Hon-17 BA 76 1.6 35.6 2.8 6.3 5.1 21.4 37.2 27.2 22.4 1.62 

98 Hon-17 Btl 100 1.1 32.5 2.3 5.8 4.2 20.2 37.9 29.6 24.7 1.76 

99 Hon-17 Bt2 160 0.0 26.7 0.8 2.0 1.9 22.0 40.2 33.1 28.7 1.86 

100 Hon-17 2BCt 201 0.0 47.7 8.4 23.5 5.4 10.4 27.5 24.8 21.4 1.90 

101 Hon-17 3BCt 208 0.0 33.4 2.5 8.1 4.8 18.0 39.7 26.9 22.9 1.88 

102 Hon-17 4BCt 295 35.0 66.3 16.2 20.3 14.5 15.3 13.1 20.6 18.1 1.70 

103 Hon-18 Apl 19 4.0 42.3 4.2 7.6 5.9 24.6 40.9 16.8 13.1 1.69 

104 Hon-18 Ap2 30 3.0 39.2 3.6 7.3 5.7 22.5 43.7 17.1 13.7 1.58 

105 Hon-18 BA 90 1.4 34.5 2.4 6.0 4.7 21.5 40.0 25.5 21.2 1.54 

106 Hon-18 Btl 113 0.7 29.0 1.8 4.3 3'.5 19.4 41.9 29.1 25.1 1.76 

107 Hon-18 Bt2 170 0.0 17.2 0.6 2.3 1.1 13.2 48.9 33.9 30.2 1.93 

108 Hon-18 2BCt 190 0.4 32.6 5.0 16.5 3.2 7.8 39.4 28.0 25.1 1.95 

109 Hon-18 3BCt 240 0.3 32.0 0.9 5.5 6.8 18.8 38.9 29.1 25.3 2.20 

110 Hon-18 4BCt 300 35.0 63.6 13.1 18.8 14.8 16.8 15.6 20.8 18.8 1.89 

111 Hon-19 Apl 7 1.6 43.6 2.9 7.8 7.1 25.8 40.2 16.2 12.0 1.45 

112 Hon-19 Ap2 24 1.5 42.5 3.0 7.6 6.9 25.0 38.4 19.1 14.9 1.64 

113 Hon-19 BA 63 1.0 40.6 3.6 7.4 6.3 23.3 35.8 23.6 19.4 1.56 

114 Hon-19 Btl 91 1.0 40.0 2.8 7.6 6.4 23.2 36.2 23.8 20.0 1.75 

115 Hon-19 Bt2 126 0.6 34.6 1.7 6.6 4.8 21.5 32.2 33.2 28.6 1.88 

116 Hon-19 Bt3 176 1.4 34.6 1.8 4.0 3.6 25.2 31.4 34.0 29.1 1.87 

117 Hon-19 BCt 218 0.6 46.1 2.2 4.8 4.1 35.0 27.4 26.5 23.4 1.92 

118 Hon-19 2BCtl 246 4.8 65.5 10.7 22.9 12.3 18.6 14.3 20.2 18.6 1.88 

119 Hon-19 2BCt2 268 7.4 72.4 9.0 28.5 17.7 17.2 12.2 15.4 12.1 1.77 

120 Hon-19 2BCt3 300 6.7 75.7 9.6 31.5 19.0 15.6 10.6 13.7 12.5 1.72 

121 Hon-19 3Cox 320 15.2 82.4 24.3 36.9 13.9 7.3 7.1 10.5 9.6 0.00 

122 Hon-19 3Cox 410 0.0 79.6 18.8 35.1 15.8 9.9 7.2 13.2 11.9 0.00 

123 Hon-20 Apl 11 1.8 43.8 3.1 7.8 6.9 26.0 39.4 16.8 12.8 1.48 

124 Hon-20 Ap2 30 1.2 43.1 2.9 7.9 7.0 25.3 38.7 18.2 14.3 1.63 

125 Hon-20 BA 60 1.0 40.1 2.4 7.0 6.6 24.1 36.1 23.8 19.9 1.59 

126 Hon-20 Btl 114 0.7 39.3 2.1 7.3 6.4 23.5 36.0 24.7 20.5 1.73 

127 Hon-20 Bt2 191 0.3 34.6 2.0 4.2 3.9 24.5 32.0 33.4 29.1 1.90 

G82 Soil Cbronosequences in the Western United States 
Supplementary table 2. Physical properties-Continued 

Percentage of <2-mm fraction 

Sample Profile Horizon Basal >2 mm Total vco co m fi+vfi Silt <2-J,Lm <1-J.Lm Bulk 

number number depth sand sand sand sand sand clay clay density 

(em) (g/cm3) 

Lower member of the Riverbank Formation, 250 ka-Continued 

128 Hon-20 2BCtl 223 1.8 57.7 5.8 12.6 10.5 28.8 20.3 22.0 19.9 1.88 

129 Hon-20 2BCt2 260 9.9 70.3 11.2 23.5 17.8 17.9 11.5 18.2 16.6 1.78 

130 Hon-20 2CB 283 8.5 81.9 17.4 36.5 17.3 10.7 6.7 11.4 10.7 1.77 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 4.0 60.1 3.4 14.8 13.6 28.3 21.6 18.3 15.2 1.62 

132 Hon-21 AB 33 1.0 53.0 2.8 13.8 12.1 24.3 22.1 24.9 21.1 1.78 

133 Hon-21 BA 46 7.0 45.7 2.1 10.4 10.0 23.2 24.8 29.5 25.5 1.57 

134 Hon-21 Btl 71 7.0 29.5 2.0 6.9 5.9 14.7 19.6 50.9 47.2 1.71 

135 Hon-21 Bt2 93 7.0 26.7 1.7 6.9 5.5 12.6 18.8 54.5 50.3 1.84 

136 Hon-21 Bt3 119 7.0 29.9 2.7 8.3 5.9 13.0 19.4 50.7 46.5 1.81 

137 Hon-21 Bt4 148 7.0 33.2 3.3 9.2 6.8 13.9 18.8 48.0 43.4 1.78 

138 Hon-21 2Btl 197 20.0 33.9 3.6 9.8 7.5 13.0 21.3 44.6 39.2 1.80 

139 Hon-21 2Bt2 274 20.0 39.8 4.8 12.5 9.1 13.4 25.1 35.2 30.5 1.72 

140 Hon-21 2BC 315 25.0 38.8 4.6 11.4 7.7 15.0 27.7 33.4 28.9 1.66 

141 Hon-21 3BC 473 55.0 44.5 5.6 12.9 9.2 16.8 28.8 26.4 22.6 1.72 

142 Hon-21 c 1300 0.0 78.3 20.1 33.9 12.8 11.6 9.6 11.5 8.1 0.00 

143 Hon-22 A 23 3.0 56.4 2.8 14.8 13.6 25.2 21.7 21.5 17.9 1.74 

144 Hon-22 AB 43 7.0 46.6 2.0 10.2 11.0 23.4 24.1 29.1 25.1 1.36 

145 Hon-22 BA 59 7.0 34.7 2.1 8.7 7.8 16.1 21.5 43.9 39.9 1.63 

146 Hon-22 Btl 89 7.0 25.0 2.0 6.2 5.3 12.3 19.5 54.5 50.6 1.83 

147 Hon-22 Bt2 120 7.0 28.1 2.6 7.4 5.9 12.1 20.3 51.4 46.7 1.83 

148 Hon-22 Bt3 154 7.0 28.4 2.0 7.6 5.2 13.5 20.2 51.4 47.1 1.82 

149 Hon-22 2Btl 207 20.0 32.5 2.5 10.0 7.3 12.7 20.4 47.2 41.8 1.93 

150 Hon-22 2Bt2 270 30.0 36.0 3.8 12.1 7.5 12.6 24.6 39.4 33.8 1.68 

151 Hon-22 2BCt 342 35.0 43.0 6.5 15.6 8.0 12.8 26.9 30.2 25.8 1.62 

152 Hon-22 3BCtl 445 60.0 47.4 10.8 10.4 7.5 18.7 29.2 23.4 20.2 1.73 

153 Hon-22 3BCt2 505 70.0 40.5 9.1 9.9 6.4 15.0 25.1 34.4 30.7 2.12 

154 H~n-22 c 1300 0.0 69.3 16.3 37.8 8.0 7.2 13.0 17.7 16.2 0.00 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 0.0 86.2 17.1 35.4 17.0 16.7 8.0 5.8 4.6 0.00 

156 Hon-72 Cn 0 0.0 93.5 1.4 32.7 44.5 14.9 3.7 2.8 2.3 0.00 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G83 
Supplementary table 3. Extractive chemical analyses 

[Analysts: A.J. Busacca and P. Janitzky] 

Percent of <2-mm fraction Percent of <2-mm fraction 

Basal Organic Basal Organic 

Sample Profile Horizon depth carbon Fed mags Sample Profile Horizon depth carbon Fed mags 

number number (em) (pet) number number (em) (pet) 

Holocene alluvium, 0.6 ka Upper member of the Modesto Fonnatlon, 10 ka--Conlinued 

1 Hon-1 A 12 2.20 2.12 51 Hon-8 Ap1 7 1.22 2.47 

2 Hon-1 2A1 16 2.22 2.16 52 Hon-8 Ap2 34 1.21 2.46 

3 Hon-1 2A2 25 1.38 1.94 53 Hon-8 BA 57 .56 2.67 

4 Hon-1 2AC 49 1.08 2.04 54 Hon-8 Bw1 90 .39 2.58 

5 Hon-1 2C 85 .85 2.06 55 Hon-8 Bw2 126 .19 2.33 

6 Hon-1 3C1 95 .64 1.86 56 Hon-8 BC1 191 .39 2.23 

7 Hon-1 3C2 122 .47 1.53 57 Hon-8 BC2 240 .30 1.89 

8 Hon-1 4Cl 140 .11 1.38 58 Hon-8 2Cox 390 .03 .94 

9 Hon-1 4C2 170 2.33 2.43 

Lower member of the Modesto Fonnatlon, 40 ka 

10 Hon-2 A1 4 .58 1.46 

11 Hon-2 A2 32 1.67 2.29 59 Hon-10 Ap 22 2.08 1.13 0.60 

12 Hon-2 c 61 .60 2.00 60 Hon-10 BA 40 .62 1.35 .55 

13 Hon-2 2C 92 .60 2.01 61 Hon-10 Btl 86 .40 1.35 .78 

14 Hon-2 3C 103 .54 2.09 62 Hon-10 Bt2 132 .49 1.47 .75 

15 Hon-2 4C 130 .26 1.67 63 Hon-10 BC 150 .39 1.31 .87 

64 Hon-10 c 205 .28 1.22 1.13 

16 Hon-3 A1 4 3.27 2.41 65 Hon-10 2C 225 .16 1.27 .29 

17 Hon-3 A2 16 1.60 2.43 

18 Hon-3 AC 31 1.25 2.3'7 66 Hon-11 Ap 18 2.07 1.13 

19 Hon-3 c 54 .58 1.98 67 Hon-11 BA 45 .37 1.31 

20 Hon-3 2C 78 .56 1.99 68 Hon-11 Btl 94 .24 1.43 

69 Hon-11 Bt2 125 .17 1.47 

21 Hon-4 c 17 .81 1.66 0.58 70 Hon-11 BC 145 .16 1.37 

22 Hon-4 2A 32 1.87 2.06 .18 71 Hon-11 c 179 .13 1.18 

23 Hon-4 2AC 49 1.43 2.27 .12 72 Hon-11 2C 220 .14 1.38 

24 Hon-4 2C 86 .64 2.09 .11 

25 Hon-4 3Cl 113 .43 1.88 .44 Upper member of the Riverbank Fonnatlon, 130 ka 

26 Hon-4 3C2 147 .48 1.77 .48 

73 Hon-13 Ap 24 .92 2.44 

Upper member of the Modesto Fonnatlon, 10 ka 74 Hon-13 BA 33 .31 2.69 

75 Hon-13 BAt1 50 .24 2.81 

27 Hon-5 Apl 13 1.52 2.69 0.02 76 Hon-13 BAt2 62 .13 2.73 

28 Hon-5 Ap2 23 1.38 2.71 .02 77 Hon-13 Btl 86 .18 2.64 

29 Hon-5 BA 54 .87 2.89 .01 78 Hon-13 Bt2 102 .19 2.25 

30 Hon-5 Bwl 88 .51 2.79 .03 79 Hon-13 Bt3 123 .12 2.30 

31 Hon-5 Bw2 102 .35 2.75 .05 80 Hon-13 BCt 157 .11 2.35 

32 Hon-5 BCl 141 .20 2.67 .02 81 Hon-13 2BCtl 208 .08 1.75 

33 Hon-5 BC2 180 .18 2.46 .02 82 Hon-13 2BCt2 245 .08 1.84 

83 Hon-13 2BCt3 266 .07 1.70 

34 Hon-6 Apl 10 1.50 2.63 84 Hon-13 2CB 301 .07 1.65 

35 Hon-6 Ap2 22 1.27 2.65 

36 Hon-6 BA 43 .97 2.74 85 Hon-14 Ap 28 .82 2.38 .01 

37 Hon-6 Bw1 91 .59 2.54 86 Hon-14 BA 39 .35 2.68 .00 

38 Hon-6 Bw2 118 .40 2.52 87 Hon-14 BAtl 59 .23 2.79 .01 

39 Hon-6 BC1 157 .21 2.46 88 Hon-14 BAt2 76 .24 3.07 .00 

40 Hon-6 BC2 184 .18 2.22 89 Hon-14 Btl 111 .17 2.59 .01 

90 Hon-14 Bt2 126 .11 2.27 .00 

41 Hon-7 Ap1 8 1.13 2.41 91 Hon-14 2BCtl 150 .09 2.08 .01 

42 Hon-7 Ap2 30 1.06 2.46 92 Hon-14 2BCt2 200 .07 1.76 .02 

43 Hon-7 BA 54 .58 2.76 93 Hon-14 2BCt3 260 .07 1.86 .03 

44 Hon-7 Bw1 88 .51 2.63 94 Hon-14 2CB 320 .08 1.72 

45 Hon-7 Bw2 118 .27 2.41 

46 Hon-7 BC 180 .15 2.27 Lower member of the Riverbank Fonnatlon, 250 ka 

47 Hon-7 2BC 230 .19 2.08 

48 Hon-7 3Cox 290 .21 1.59 

49 Hon-7 4Cox 340 .11 1.06 95 Hon-17 Ap1 18 .89 1.99 

50 Hon-7 4Cn 370 .10 .96 96 Hon-17 Ap2 24 .74 2.18 

G84 Soil Chronosequences in the Western United States 
Supplementary table 3. Extractive chemical analyses- Continued 

Basal Percent of <2-mm fraction Basal Percent of <2-mm fraction 

Sample Profile Horizon depth Organic Fed mags Sample Profile Horizon depth Organic Fed mags 

number number (em) carbon (pet) number number (em) carbon (pet) 

Lower member of the Riverbank Formation, 250 ka-Conlinued Lower member of the Rlverllank Formation, 250 ka-Conlinued 

97 Hon-17 BA 76 .26 2.82 129 Hon-20 2BCt2 260 .04 1.78 

98 Hon-17 Btl 100 .16 2.88 130 Hon-20 2CB 283 .13 1.59 

99 Hon-17 Bt2 160 .11 2.78 

100 Hon-17 2BCt 201 .09 2.21 Exhumed lower member of the Laguna Formation, 1,600 ka 

101 Hon-17 3BCt 208 .07 2.16 

102 Hon-17 4BCt 295 .07 1.89 131 Hon-21 A 11 1.23 2.49 0.13 

132 Hon-21 AB 33 .80 2.89 .06 

103 Hon-18 Apl 19 .88 2.14 .03 133 Hon-21 BA 46 .55 3.50 .10 

104 Hon-18 Ap2 30 .77 2.23 .02 134 Hon-21 Btl 71 .37 4.35 .04 

105 Hon-18 BA 90 .23 2.71 .02 135 Hon-21 Bt2 93 .25 4.71 .03 

106 Hon-18 Btl 113 .15 2.82 .01 136 Hon-21 Bt3 119 .22 4.67 .04 

107 Hon-18 Bt2 170 .09 1.93 .00 137 Hon-21 Bt4 148 .23 4.88 .02 

108 Hon-18 2BCt 190 .08 2.11 .01 138 Hon-21 2Btl 197 .21 5.01 .01 

109 Hon-18 3BCt 240 .09 2.07 .00 139 Hon-21 2Bt2 274 .17 4.79 .01 

110 Hon-18 4BCt 300 .06 1.90 .01 140 Hon-21 2BC 315 .20 4.39 .02 

141 Hon-21 3BC 473 .15 2.61 .02 

111 Hon-19 Apl 7 1.73 1.97 142 Hon-21 c 1300 .05 1.66 .90 

112 Hon-19 Ap2 24 .68 2.22 

113 Hon-19 BA 63 .27 2.54 143 Hon-22 A 23 1.22 2.74 

114 Hon-19 Btl 91 .23 2.52 .144 Hon-22 AB 43 .68 3.46 

115 Hon-19 Bt2 126 .14 2.88 145 Hon-22 BA 59 .18 4.31 

116 Hon-19 Bt3 176 .13 2.86 146 Hon-22 Btl 89 .19 4.83 

117 Hon-19 BCt 218 .12 2.28 147 Hon-22 Bt2 120 .16 4.79 

118 Hon-19 2BCtl 246 .11 1.84 148 Hon-22 Bt3 154 .18 4.86 

119 Hon-19 2BCt2 268 .09 1.64 149 Hon-22 2Btl 207 .15 4.90 

120 Hon-19 2BCt3 300 .08 1.67 150 Hon-22 2Bt2 270 .16 4.64 

121 Hon-19 3Cox 320 .08 1.42 151 Hon-22 2BCt 342 .13 3.91 

122 Hon-19 3Cox 410 .08 1.69 152 Hon-22 3BCtl 445 .13 2.23 

153 Hon-22 3BCt2 505 .14 2.04 

123 Hon-20 Apl 11 1.57 2.14 154 Hon-22 c 1300 .05 1.49 

124 Hon-20 Ap2 30 .62 2.28 

125 Hon-20 BA 60 .26 2.59 Modern alluvium, 0 ka 

126 Hon-20 ]~tl 114 .17 2.63 

127 Hon-20 Bt2 191 .04 1.99 155 Hon-71 Cn 0 .62 1.06 

128 Hon-20 2BCtl 223 .10 2.93 156 Hon-72 Cn 0 .13 .51 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G85 
Supplementary table 4, part 1. Clay mineralogy of the coarse (0.2-2 J.Lm) fraction 

[Clay minerals: +,trace;++, moderate;+++, abundant;++++, clearly dominant;-, not detennined. Primary minerals: X, moderate; 

XX, abundant;-, not detennined. Analysts: H. Foolad and AJ. Busacca] 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Holocene alluvium, 0.6 ka 

1 Hon-1 A 12 

2 Hon-1 2A1 16 

3 Hon-1 2A2 25 

4 Hon-1 2AC 49 

5 Hon-1 2C 85 

6 Hon-1 3C1 95 

7 Hon-1 3C2 122 

8 Hon-1 4C1 140 

9 Hon-1 4C2 170 

10 Hon-2 A1 4 

11 Hon-2 A2 32 

12 Hon-2 c 61 

13 Hon-2 2C 92 

14 Hon-2 3C 103 

15 Hon-2 4C 130 

16 Hon-3 A1 4 

17 Hon-3 A2 16 

18 Hon-3 AC 31 

19 Hon-3 c 54 

20 Hon-3 2C 78 

21 Hon-4 c 17 

22 Hon-4 2A 32 +++ +++ ++ +++ + ++ ++ X X 

23 Hon-4 2AC 49 

24 Hon-4 2C 86 +++ + ++ ++++ + + X X 

25 Hon-4 3C1 113 

26 Hon-4 3C2 147 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 Ap1 13 

28 Hon-5 Ap2 23 +++ + ++ ++++ + X X 

29 Hon-5 BA 54 

30 Hon-5 Bw1 88 +++ ++ ++++ + X X 

31 Hon-5 Bw2 102 

32 Hon-5 BC1 141 

33 Hon-5 BC2 180 ++ ++++ + + X X 

34 Hon-6 Ap1 10 

35 Hon-6 Ap2 22 

36 Hon-6 BA 43 

37 Hon-6 Bw1 91 

38 Hon-6 Bw2 118 

39 Hon-6 BC1 157 

40 Hon-6 BC2 184 

41 Hon-7 Ap1 8 

42 Hon-7 Ap2 30 

G86 Soil Chronosequences in the Western United States 
Supplementary table 4, part 1. Clay mineralogy of the coarse (0.2-2 J.Lm) fraction-Continued 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Upper member of the Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 

44 Hon-7 Bwl 88 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 Apl 7 

52 Hon-8 Ap2 34 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 

55 Hon-8 Bw2 126 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 

58 Hon-8 2Cox 390 

Lowe,r member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 ++ + ++ ++++ +++ + X X 

60 Hon-10 BA 40 

61 Hon-10 Btl 86 

62 Hon-10 Bt2 132 ++ + ++ ++++ +++ + X X 

63 Hon-10 BC 150 

64 Hon-10 c 205 ++ + ++ ++++ +++ + X X 

65 Hon-10 2C 225 

66 Hon-11 Ap 18 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 

70 Hon-11 BC 145 

71 Hon-11 c 179 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

85 Hon-14 Ap 28 +++ + +++ ++ + + XX X 

86 Hon-14 BA 39 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G87 
Supplementary table 4, part 1. Clay mineralogy of the coarse (0.2-2 J..Lm) fraction-Continued 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Upper member of the Riverbank Formation, 130 ika-Continued 

87 Hon-14 BAtl 59 

88 Hon-14 BAt2 76 

89 Hon-14 Btl 111 +t+ + +t++ + + + XX X 

90 Hon-14 Bt2 126 

91 Hon-14 2BCtl 150 

92 Hon-14 2BCt2 200 

93 Hon-14 2BCt3 260 ++ + + +t++ + + + X XX 

94 Hon-14 2CB 320 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 

97 Hon-17 BA 76 

98 Hon-17 Btl 100 

99 Hon-17 Bt2 160 

100 Hon-17 2BCt 201 

101 Hon-17 3BCt 208 

102 Hon-17 4BCt 295 

103 Hon-18 Apl 19 

104 Hon-18 Ap2 30 +t+ + + +t+ +t+ + XX X 

105 Hon-18 BA 90 

106 Hon-18 Btl 113 +t+ ++ +t++ ++ + XX X 

107 Hon-18 Bt2 170 +t+ ++++ + + X XX 

108 Hon-18 2BCt 190 

109 Hon-18 3BCt 240 

110 Hon-18 4BCt 300 

111 Hon-19 Apl 7 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

123 Hon-20 Apl 11 

124 Hon-20 Ap2 30 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 

128 Hon-20 2BCtl 223 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

G88 Soil Chronosequences in the Western United States 
Supplementary table 4, part 1. Clay mineralogy of the coarse (0.2-2 f.Lm) fraction-Continued 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 ++++ + ++ + XX X 

132 Hon-21 AB 33 

133 Hon-21 BA 46 

134 Hon-21 Btl 71 

135 Hon-21 Bt2 93 ++++ + ++ + XX X 

136 Hon-21 Bt3 119 

137 Hon-21 Bt4 148 

138 Hon-21 2Bt1 197 

139 Hon-21 2Bt2 274 

140 Hon-21 2BC 315 

141 Hon-21 3BC 473 +++ + ++++ + X X 

142 Hon-21 c 1300 

143 Hon-22 A 23 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Bt1 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCt1 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 

156 Hon-72 Cn 0 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G89 
Supplementary table 4, part 2. Clay mineralogy of the fine (<0.2 J.Lm) fraction 

[Clay Minerals: +,trace;++, moderate;+++, abundant;++++, clearly dominant;-, not determined. Primary minerals: X, moderate; 

XX, abundant;-. not detennined. Analysts: H. Foolad and AJ. Busacca] 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Holocene alluvium, 0.6 ka 

1 Hon-1 A 12 

2 Hon-1 2A1 16 

3 Hon-1 2A2 25 

4 Hon-1 2AC 49 

5 Hon-1 2C 85 

6 Hon-1 3C1 95 

7 Hon-1 3C2 122 

8 Hon-1 4B1b 140 

9 Hon-1 4B2b 170 

10 Hon-2 A1 4 

11 Hon-2 A2 32 

12 Hon-2 c 61 

13 Hon-2 2C 92 

14 Hon-2 3C 103 

15 Hon-2 4B2tb 130 

16 Hon-3 A1 4 

17 Hon-3 A2 16 

18 Hon-3 AC 31 

19 Hon-3 c 54 

20 Hon-3 2C 78 

21 Hon-4 c 17 

22 Hon-4 2A 32 ++ +++ X X 

23 Hon-4 2AC 49 

24 Hon-4 2C 86 ++ ++++ XX X 

25 Hon-4 3C1 113 

26 Hon-4 3C2 147 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 AP1 13 

28 Hon-5 AP2 23 ++ + +++ X X 

29 Hon-5 BA 54 

30 Hon-5 Bw1 88 +++ ++ ++++ X X 

31 Hon-5 Bw2 102 

32 Hon-5 BC1 141 

33 Hon-5 BC2 180 +++ ++ ++++ XX X 

34 Hon-6 AP1 10 

35 Hon-6 AP2 22 

36 Hon-6 BA 43 

37 Hon-6 Bw1 91 

38 Hon-6 Bw2 118 

39 Hon-6 BC1 157 

40 Hon-6 BC2 184 

41 Hon-7 AP1 8 

42 Hon-7 AP2 30 

G90 Soil Chronosequences in the Western United States 
Supplementary table 4, part 2. Clay mineralogy of the fine (<0.2 J.Lm) fraction-Continued 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Upper member of tbe Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 

44 Hon-7 Bwl 88 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 APl 7 

52 Hon-8 AP2 34 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 

55 Hon-8 Bw2 126 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 

58 Hon-8 2Cox 390 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 +++ + ++ + + X X 

60 Hon-10 BA 40 

61 Hon-10 Btl 86 

62 Hon-10 Bt2 132 +++ + + X X 

63 Hon-10 BC 150 

64 Hon-10 c 205 +++ + ++ + +++ X X 

65 Hon-10 2C 225 

66 Hon-11 Ap 18 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 

70 Hon-11 BC 145 

71 Hon-11 c 179 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G91 
Supplementary table 4, part 2. Clay mineralogy of the fine (<0.2 J.Lm) fraction-Continued 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Upper member of the Riverbank Formation, 130 km-Continued 

85 Hon-14 Ap 28 ++++ X X 

86 Hon-14 BA 39 

87 Hon-14 BAtl 59 

88 Hon-14 BAt2 76 

89 Hon-14 Btl 111 +++ + +++ + X X 

90 Hon-14 Bt2 126 

91 Hon-14 2BCtl 150 

92 Hon-14 2BCt2 200 

93 Hon-14 2BCt3 260 +++ + + + +++ X X 

94 Hon-14 2CB 320 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 

97 Hon-17 BA 76 

98 Hon-17 Btl 100 

99 Hon-17 Bt2 160 

100 Hon-17 2BCt 201 

101 Hon-17 3BCt 208 

102 Hon-17 4BCt 295 

103 Hon-18 Apl 19 

104 Hon-18 Ap2 30 ++++ + + X X 

105 Hon-18 BA 90 

106 Hon-18 Btl 113 ++++ + ++ + X X 

107 Hon-18 Bt2 170 +++ +++ ++ X X 

108 Hon-18 2BCt 190 

109 Hon-18 3BCt 240 

110 Hon-18 4BCt 300 

111 Hon-19 Apl 7 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

123 Hon-20 Apl 11 

124 Hon-20 Ap2 30 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 

128 Hon-20 2BCtl 223 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

G92 Soil Chronosequences in the Western United States 
Supplementary table 4, part 2. Clay mineralogy of the fine (<0.2 tJ.m) fraction-Continued 

Basal Chloritized 

Sample Profile Horizon depth Kaolin Chlorite vermic- Vermic- Mica Smectite Talc Quartz Feldspar 

number number (em) ulite ulite 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 ++++ + X X 

132 Hon-21 AB 33 

133 Hon-21 BA 46 

134 Hon-21 Btl 71 

135 Hon-21 Bt2 93 ++++ + X X 

136 Hon-21 Bt3 119 

137 Hon-21 Bt4 148 

138 Hon-21 2Btl 197 

139 Hon-21 2Bt2 274 

140 Hon-21 2BC 315 

141 Hon-21 3BC 473 +++ + ++ + X x· 

142 Hon-21 c 1300 

143 Hon-22 A 23 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Btl 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCtl 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 

156 Hon-72 Cn 0 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G93 
Supplementary table 5. Total chemical analyses of the fine (<50 IJ.m) fraction by X-ray fluorescence 

[All values in weight percent. Analysts: J. Baker, A. Bartell, J. Taggart, and J.S. Wahlberg] 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Holocene alluvium, 0.6 ka 

I Hon-I A I2 

2 Hon-I 2AI I6 

3 Hon-I 2A2 25 50.4 I7.9 Il.O 2.94 4.8I 1.96 0.64 1.35 O.I5 O.IS 

4 Hon-I 2AC 49 

5 Hon-I 2C 85 49.7 IS. I I1.4 2.95 5.04 1.86 .57 1.39 .13 .20 

6 Hon-I 3CI 95 

7 Hon-I 3C2 I22 

8 Hon-I 4Bib I40 

9 Hon-I 4B2b I70 

IO Hon-2 AI 4 

11 Hon-2 A2 32 50.3 I8.2 I0.9 2.86 4.64 1.95 .65 1.29 .I7 .I9 

I2 Hon-2 c 6I 

I3 Hon-2 2C 92 49.0 I8.2 I1.3 2.80 4.87 1.89 .59 1.39 .I3 .2I 

I4 Hon-2 3C I03 

I5 Hon-2 4B2tb I30 

I6 Hon-3 AI 4 

I7 Hon-3 A2 I6 50.9 I8.3 I0.6 2.85 4.60 1.99 .65 1.26 .I7 .I7 

IS Hon-3 AC 3I 

I9 Hon-3 c 54 48.8 I8.2 I1.3 2.85 4.80 1.80 .60 1.34 .I3 .22 

20 Hon-3 2C 78 

2I Hon-4 c I7 

22 Hon-4 2A 32 49.9 IS.O Il.O 2.83 4.88 1.93 .60 1.32 .26 .I7 

23 Hon-4 2AC 49 

24 Hon-4 2C 86 49.5 I8.2 I1.4 2.95 4.95 1.90 .58 1.37 .I4 .20 

25 Hon-4 3CI 113 

26 Hon-4 3C2 I47 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 API I3 

28 Hon-5 AP2 23 50.4 I8.6 I0.9 2.54 4.IO 1.99 .50 1.32 .I5 .IS 

29 Hon-5 BA 54 

30 Hon-5 Bwi 88 50.2 I8.3 I0.9 2.60 4.25 2.06 .45 1.35 .IO .20 

3I Hon-5 Bw2 I02 

32 Hon-5 BCI I4I 

33 Hon-5 BC2 ISO 

34 Hon-6 API IO 

35 Hon-6 AP2 22 50.4 I8.6 Il.O 2.48 4.07 2.0I .49 1.33 .I4 .IS 

36 Hon-6 BA 43 

37 Hon-6 Bwi 9I 52.2 I7.6 IO.O 2.67 4.85 2.36 .46 1.39 .I2 .I7 

38 Hon-6 Bw2 118 

39 Hon-6 BCI I 57 

40 Hon-6 BC2 I84 

4I Hon-7 API 8 

42 Hon-7 AP2 30 51.7 I8.4 I0.7 2.25 4.43 2.I9 .57 1.46 .I4 .20 

G94 Soil Chronosequences in the Western United States 
Supplementary table 5. Total chemical analyses of the fine (<50 f..l.m) fraction by X-ray fluorescence-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Upper member of tbe Modesto Formation, 10 ka-Continued 

43 Hon-7 BA ·54 

44 Hon-7 Bwl 88 50.2 18.7 11.0 2.38 4.00 2.03 .48 1.37 .11 .22 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 APl 7 

52 Hon-8 AP2 34 51.5 18.5 10.8 2.23 4.36 2.10 .58 1.49 .14 .19 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 50.4 18.5 10.8 2.44 4.13 2.11 .48 1.38 .10 .22 

55 Hon-8 Bw2 126 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 53.2 17.5 9.69 2.77 3.71 2.35 .54 1.22 .05 .20 

58 Hon-8 2Cox 390 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 54.5 17.5 8.84 2.95 2.87 1.63 1.66 1.09 0.41 0.14 

60 Hon-10 BA 40 

61 Hon-10 Btl 86 

62 Hon-10 Bt2 132 51.5 19.9 9.81 3.09 2.40 1.38 1.69 1.04 .30 .20 

63 Hon-10 BC 150 

64 Hon-10 c 205 52.1 19.1 9.76 3.31 2.78 1.54 1.55 1.05 .22 .20 

65 Hon-10 2C 225 

66 Hon-11 Ap 18 54.6 17.3 8.67 2.84 2.71 1.57 1.64 1.07 .37 .13 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 51.6 20.0 9.78 3.02 2.46 1.42 1.62 1.03 .30 .20 

70 Hon-11 BC 145 

71 Hon-11 c 179 51.9 19.1 9.81 3.36 2.75 1.48 1.59 1.05 .23 .20 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 60.5 16.9 7.64 .77 3.24 1.75 1.05 1.17 .12 .20 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 50.2 20.2 10.5 2.00 2.24 1.32 .50 .95 .05 .05 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCt1 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G95 
Supplementary table 5. Total chemical analyses of the fine (<50 f.Lm) fraction by X-ray fluorescence-Continued 

Basal 

Sample Profile Horizon depth SiOZ Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 PzOs MnO 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

85 Hon-14 Ap 28 60.0 16.9 7.76 .80 3.16 1.71 1.05 1.18 .12 .20 

86 Hon-14 BA 39 

87 Hon-14 BAtl 59 

88 Hon-14 BAt2 76 

89 Hon-14 Btl 111 51.3 20.6 10.2 1.62 2.06 1.19 .93 1.11 .07 .21 

90 Hon-14 Bt2 126 

91 Hon-14 2BCtl 150 

92 Hon-14 2BCt2 200 

93 Hon-14 2BCt3 260 

94 Hon-14 2CB 320 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 55.5 18.9 9.08 1.10 3.85 1.47 1.34 1.20 .16 .20 

97 Hon-17 BA 76 

98 Hon-17 B'tl 100 

99 Hon-17 Bt2 160 49.9 20.5 10.7 1.69 3.34 1.50 .74 1.07 .08 .19 

100 Hon-17 2BCt 201 

101 Hon-17 · 3BCt 208 51.7 19.3 10.0 1.92 3.56 1.73 .71 1.01 .06 .17 

102 Hon-17 4BCt 295 

103 Hon-18 Apl 19 

104 Hon-18 Ap2 30 55.7 18.6 8.98 1.08 3.90 1.49 1.32 1.21 .16 .18 

105 Hon-18 BA 90 

106 Hon-18 Btl 113 

107 Hon-18 Bt2 170 51.5 19.8 10.4 1.98 3.53 1.75 .62 1.02 .06 .18 

108 Hon-18 2BCt 190 

109 Hon-18 3BCt 240 52.1 19.1 10.4 2.21 3.45 1.78 .68 1.01 .06 .16 

110 Hon-18 4BCt 300 

111 Hon-19 Apl 7 55.2 18.8 9.03 1.06 3.35 1.36 1.39 1.23 .14 .26 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 49.2 20.9 11.3 1.83 2.86 1.33 .78 1.11 .08 .20 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

123 Hon-20 Apl 11 

124 Hon-20 Ap2 30 55.6 18.7 8.98 1.04 3.35 1.43 1.39 1.22 0.14 0.23 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 48.9 20.8 11.1 1.69 2.83 1.33 .81 1.11 .08 .17 

128 Hon-20 2BCtl 223 

G96 Soil Chronosequences in the Western United States 
Supplementary table 5. Total chemical analyses of the fine (<50 1-Lm) fraction by X-ray fluorescence-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Lower member of the Riverbank Formation, 250 k~ontinued 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 53.7 20.1 10.3 .63 .84 .29 1.19 1.47 .25 .14 

132 Hon-21 AB 33 

133 Hon-21 BA 46 

134 Hon-21 Btl 71 

135 Hon-21 Bt2 93 47.5 26.0 10.9 .54 .15 .15 .87 1.10 .16 .07 

136 Hon-21 Bt3 119 

137 Hon-21 Bt4 148 

138 Hon-21 2Btl 197 45.3 27.0 12.0 .51 .16 .15 .72 .96 .14 .03 

139 Hon-21 2Bt2 274 

140 Hon-21 2BC 315 

141 Hon-21 3BC 473 

142 Hon-21 c 1300 

143 Hon-22 A 23 52.0 20.5 10.3 .60 .97 .29 1.16 1.45 .25 .18' 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 47.6 25.9 11.0 .55 .24 .15 .88 1.12 .18 .09 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Btl 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCtl 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 47.7 21.3 10.7 1.97 2.75 1.66 .51 .92 .07 .14 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 

156 Hon-72 Cn 0 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G97 
Supplementary table 6, part 1. Total chemical analyses of the 2-20 ~m fraction by X-ray fluorescence for major oxides 

[All values in weight percenL Analyst: A.J. Busacca] 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20S MnO 

number number (em) 

Holocene alluvium, 0.6 ka 

I Hon-I A I2 

2 Hon-I 2AI I6 

3 Hon-I 2A2 25 

4 Hon-I 2AC 49 

5 Hon-I 2C 85 

6 Hon-I 3CI 95 

7 Hon-I 3C2 I22 

8 Hon-I 4Bib I40 

9 Hon-I 4B2b I70 

IO Hon-2 AI 4 

11 Hon-2 A2 32 

I2 Hon-2 c 6I 

I3 Hon-2 2C 92 

I4 Hon-2 3C I03 

I5 Hon-2 4B2tb I30 

16 Hon-3 A1 4 

17 Hon-3 A2 16 

18 Hon-3 AC 31 

I9 Hon-3 c 54 

20 Hon-3 2C 78 

2I Hon-4 c 17 52.90 I8.50 II.63 5.69 4.71 2.55 0.89 1.37 0.22 

22 Hon-4 2A 32 53.12 18.69 11.41 4.97 4.58 2.33 .83 1.27 .20 

23 Hon-4 2AC 49 53.68 18.42 I1.02 5.09 4.54. 2.81 .78 1.23 .2I 

24 Hon-4 2C. 86 52.34 18.67 11.52 4.85 4.60 2.29 .78 1.26 .24 

25 Hon-4 3C1 113 51.9I I8.48 11.78 5.19 4.52 2.6I .76 1.34 .25 

26 Hon-4 3C2 147 51.76 19.30 Il.74 5.10 4.55 2.34 .79 1.45 .23 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 API I3 55.04 18.37 I0.29 4.43 4.2I 2.88 .66 1.28 .20 

28 Hon-5 AP2 23 54.19 18.72 10.47 4.33 4.19 2.97 .64 1.30 .21 

29 Hon-5 BA 54 53.07 I8.22 10.59 4.3I 4.34 2.3I .60 1.30 .21 

30 Hon-5 Bw1 88 52.49 19.65 I1.69 4.61 3.98 2.48 .60 1.33 .26 

31 Hon-5 Bw2 102 52.79 19.08 11.26 5.03 4.02 2.93 .58 1.32 .26 

32 Hon-5 BC1 I41 53.64 18.47 10.62 5.5I 3.97 2.96 .6I 1.2I .24 

33 Hon-5 BC2 ISO 53.55 I8.15 10.67 5.50 3.98 2.98 .60 1.23 .25 

34 Hon-6 API IO 

35 Hon-6 AP2 22 

36 Hon-6 BA 43 

37 Hon-6 Bwi 9I 

38 Hon-6 Bw2 118 

39 Hon-6 BC1 157 

40 Hon-6 BC2 184 

41 Hon-7 AP1 8 

42 Hon-7 AP2 30 

G98 Soil Chronosequences in the Western United States 
Supplementary table 6, part 1. Total chemical analyses of the 2-20 1-Lm fraction by X-ray fluorescence for major 

oxides-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 PlOS MnO 

number number (em) 

Upper member of the Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 

44 Hon-7 Bwl 88 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 API 7 

52 Hon-8 AP2 34 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 

55 Hon-8 Bw2 126 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 

58 Hon-8 2Cox 390 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 59.73 17.28 8.08 4.97 2.49 2.04 1.96 1.08 0.14 

60 Hon-10 BA 40 57.46 18.95 9.21 5.50 2.30 2.05 2.04 1.12 .20 

61 Hon-10 Btl 86 57.01 18.76 9.26 5.44 2.20 2.08 2.05 1.12 .18 

62 Hon-10 Bt2 132 56.82 18.98 9.22 5.59 2.27 2.15 2.05 1.10 .17 

63 Hon-10 BC 150 56.99 18.89 9.24 5.77 2.51 2.06 2.02 1.11 .18 

64 Hon-10 c 205 56.54 18.60 9.35 6.07 2.59 2.37 1.94 1.10 .18 

65 Hon-10 2C 225 56.60 18.90. 9.10 5.54 2.60 2.08 1.60 .97 .18 

66 Hon-11 Ap 18 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 

70 Hon-11 BC 145 

71 Hon-11 c 179 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G99 
Supplementary table 6, part 1. Total chemical analyses of the 2-20 Jim .fraction by X-ray fluorescence for major 

oxides-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

85 Hon-14 Ap 28 65.58 15.68 6.74 .91 2.85 2.18 1.16 1.08 .20 

86 Hon-14 BA 39 64.26 16.01 6.85 .92 2.67 2.08 1.16 1.13 .22 

87 Hon-14 BAtl 59 63.71 15.84 7.01 1.03 2.61 1.97 1.18 1.12 .20 

88 Hon-14 BAt2 76 62.01 16.87 7.70 1.55 2.34 2.20 1.23 1.18 .22 

89 Hon-14 Btl 111 61.86 16.67 7.42 1.79 2.84 2.71 1.09 1.05 .23 

90 Hon-14 Bt2 126 62.17 17.23 7.52 2.10 3.40 2.83 1.05 .99 .21 

91 Hon-14 2BCtl 150 57.22 17.51 9.13 5.07 3.67 3.21 .82 .91 .15 

92 Hon-14 2BCt2 200 58.52 16.91 8.58 5.41 3.76 3.06 .72 .86 .16 

93 Hon-14 2BCt3 260 57.41 17.56 9.39 6.13 3.87 3.00 .80 .88 .21 

94 Hon-14 2CB 320 55.96 17.49 10.02 6.46 4.04 3.39 .86 .93 .28 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 

97 Hon-17 BA 76 

98 Hon-17 Btl 100 

99 Hon-17 Bt2 160 

100 Hon-17 2BCt 201 

101 Hon-17 3BCt 208 

102 Hon-17 4BCt 295 

103 Hon-18 Apl 19 62.01 16.44 7.15 1.31 3.69 2.31 1.50 1.05 .14 

104 Hon-18 Ap2 30 60.11 16.43 7.34 1.40 3.60 1.95 1.50 1.09 .19 

105 Hon-18 BA 90 59.76 17.09 7.76 1.27 3.45 1.96 1.45 1.09 .26 

106 Hon-18 Btl 113 59.46 17.40 7.79 1.70 3.50 2.66 1:20 1.07 .22 

107 Hon-18 Bt2 170 56.51 17.84 8.50 3.95 4.02 3.01 .80 .91 .20 

108 Hon-18 2BCt 190 56.30 17.45 8.00 4.44 4.08 2.97 .81 .84 ·.20 

109 Hon-18 3BCt 240 57.21 17.07 8.12 4.07 4.07 3.12 .86 .89 .19 

110 Hon-18 4BCt 300 55.42 17.74 9.39 5.32 4.55 3.23 .98 .91 .26 

111 Hon-19 Apl 7 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

23 Hon-20 Apl 11 

124 Hon-20 Ap2 30 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 

G100 Soil Chronosequences in the Western United States 
Supplementary table 6, part 1. Total chemical analyses of the 2-20 j.l.m fraction by X-ray fluorescence for major 

oxides- Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Lower member of the Riverbank Formation, 250 ka-Continued 

128 Hon-20 2BCtl 223 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 61.23 17.67 8.04 .76 1.08 .64 1.51 1.47 .21 

132 Hon-21 AB 33 62.75 17.54 8.00 .75 .98 .37 1.56 1.49 .19 

133 Hon-21 BA 46 64.21 17.86 7.91 .84 .99 .78 1.59 1.55 .18 

134 Hon-21 Btl 71 65.03 18.35 7.64 .76 .37 .25 1.59 1.54 .10 

135 Hon-21 Bt2 93 62.19 20.36 8.30 .77 .14 .22 1.44 1.47 .08 

136 Hon-21 Bt3 119 61.04 21.33 8.78 .71 .11 .24 1.36 1.35 .06 

137 Hon-21 Bt4 148 60.77 22.20 9.16 .55 .14 .00 1.47 1.44 .07 

138 Hon-21 2Btl 197 55.24 24.35 10.90 .68 .16 .26 1.30 1.28 .07 

139 Hon-21 2Bt2 274 50.12 26.68 12.80 .70 .38 .55 .99 1.02 .07 

140 Hon-21 2BC 315 50.23 24.56 13.12 .84 .98 1.02 1.08 1.01 .08 

141 Hon-21 3BC 473 51.27 21.57 11.79 1.56 3.30 2.16 .88 .87 .13 

142 Hon-21 c 1300 52.13 19.17 10.95 5.47 4.54 3.20 .86 1.21 .25 

143 Hon-22 A 23 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Btl 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCtl 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 56.82 16.09 9.68 4.99 5.20 2.78 .74 1.33 .20 

156 Hon-72 Cn 0 

late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G1 01 
Supplementary table 6, part 2. Total chemical analyses of the 20-50 IJ.m fraction by X-ray fluorescence for major oxides 

[All values in weight percent. Analyst: A.J. Busacca] 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Holocene alluvium, 0.6 ka 

1 Hon-1 A 12 

2 Hon-1 2A1 16 

3 Hon-1 2A2 25 

4 Hon-1 2AC 49 

5 Hon-1 2C 85 

6 Hon-1 3C1 95 

7 Hon-1 3C2 122 

8 Hon-1 4B1b 140 

9 Hon-1 4B2b 170 

10 Hon-2 A1 4 

11 Hon-2 A2 32 

12 Hon-2 c 61 

13 Hon-2 2C 92 

14 Hon-2 3C 103 

15 Hon-2 4B2tb 130 

16 Hon-3 A1 4 

17 Hon-3 A2 16 

18 Hon-3 AC 31 

19 Hon-3 c 54 

20 Hon-3 2C 78 

21 Hon-4 c 17 56.97 15.69 8.66 4.30 7.21 4.11 0.61 1.42 0.18 

22 Hon-4 2A 32 56.82 15.69 8.46 4.20 7.23 3.98 .62 1.36 .17 

23 Hon-4 2AC 49 56.69 15.11 8.43 4.13 7.28 4.19 .63 1.39 .18 

24 Hon-4 2C 86 55.70 15.77 8.73 4.25 7.10 3.93 .64 1.41 .18 

25 Hon-4 3C1 113 55.78 15.80 9.26 4.22 7.50 3.78 .60 1.57 .20 

26 Hon-4 3C2 147 55.49 15.09 9.29 4.34 7.73 3.74 .60 1.64 .20 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 AP1 13 59.69 14.89 7.32 3.32 6.78 4.37 .53 1.31 .15 

28 Hon-5 AP2 23 59.83 15.04 7.36 3.60 6.90 4.63 .54 1.33 .16 

29 Hon-5 BA 54 59.19 14.99 7.49 3.44 6.95 4.22 .52 1.36 .16 

30 Hon-5 Bw1 88 58.57 15.25 8.02 3.58 6.54 4.76 .52 1.39 .17 

31 Hon-5 Bw2 102 57.90 15.17 8.11 3.41 6.57 4.34 .50 1.41 .17 

32 Hon-5 BC1 141 59.55 15.75 7.58 3.65 6.54 4.37 .54 1.25 .16 

33 Hon-5 BC2 180 57.87 14.74 7.80 3.30 6.32 4.45 .52 1.30 .16 

34 Hon-6 AP1 10 

35 Hon-6 AP2 22 

36 Hon-6 BA 43 

37 Hon-6 Bw1 91 

38 Hon-6 Bw2 118 

39 Hon-6 BC1 157 

40 Hon-6 BC2 184 

41 Hon-7 AP1 8 

42 Hon-7 AP2 30 

G102 Soil Chronosequences in the Western United States 
Supplementary table 6, part 2. Total chemical analyses of the 20-50 J.Lm fraction by X-ray fluorescence for major 

oxides-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Upper member of the Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 

44 Hon-7 Bwl 88 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 API 7 

52 Hon-8 AP2 34 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 

55 Hon-8 Bw2 126 

56 Hon-8 BCI 191 

57 Hon-8 BC2 240 

58 Hon-8 2Cox 390 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 63.69 14.49 6.55 3.62 5.20 3.17 1.08 1.10 0.12 

60 Hon-10 BA 40 62.90 15.03 7.25 4.32 4.98 3.25 1.09 1.18 .14 

61 Hon-10 Btl 86 62.35 14.91 7.38 4.24 4.91 3.46 1.09 1.20 .13 

62 Hon-10 Bt2 132 62.03 14.95 7.17. 4.45 4.77 3.26 1.15 1.14 .13 

63 Hon-10 BC 150 62.62 15.37 7.07 4.28 5.13 3.42 1.09 1.11 .13 

64 Hon-10 c 205 61.92 15.59 7.19 4.50 5.21 3.13 1.13 1.08 .13 

65 Hon-10 2C 225 60.07 16.84 7.29 4.53 4.69 2.77 1.10 1.03 .13 

66 Hon-11 Ap 18 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 

70 Hon-11 BC 145 

71 Hon-11 c 179 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 

74 Hon-13 BA 33 

75 Hon-13 BAt I 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G103 
Supplementary table 6, part 2. Total chemical analyses of the 20-50 1-1m fraction by X-ray fluorescence for major 

oxides-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

85 Hon-14 Ap 28 72.09 13.21 4.71 .37 5.55 3.44 .90 .88 .11 

86 Hon-14 BA 39 70.93 13.06 4.81 .36 5.36 3.49 .89 .88 .11 

87 Hon-14 BAtl 59 69.44 12.98 4.75 .36 5.24 3.47 .87 .90 .11 

88 Hon-14 BAt2 76 68.12 13.38 5.16 .53 5.30 3.26 .87 .88 .12 

89 Hon-14 Btl 111 67.94 13.73 4.94 .56 5.56 4.23 .83 .78 .13 

90 Hon-14 Bt2 126 64.74 13.62 5.19 .79 6.10 4.12 .82 .77 .12 

91 Hon-14 2BCtl 150 61.05 14.77 6.04 1.66 6.43 4.68 .69 .74 .11 

92 Hon-14 2BCt2 200 62.51 15.04 5.78 2.80 6.05 4.97 .66 .72 .11 

93 Hon-14 2BCt3 260 60.86 15.33 6.45 3.16 6.51 4.42 .68 .76 .14 

94 Hon-14 2CB 320 60.16 14.63 6.64 3.47 6.95 4.55 .68 .77 .16 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 

97 Hon-17 BA 76 

98 Hon-17 Btl 100 

99 Hon-17 Bt2 160 

100 Hon-17 2BCt 201 

101 Hon-17 3BCt 208 

102 Hon-17 4BCt 295 

103 Hon-18 Apl 19 67.08 13.30 5.53 .48 6.36 3.41 .93 .89 .10 

104 Hon-18 Ap2 30 67.43 13.52 5.53 .49 6.36 3.38 .91 .89 .10 

105 Hon-18 BA 90 65.78 13.63 5.71 .44 6.38 3.14 .90 .93 .12 

106 Hon-18 Btl 113 66.26 13.56 5.24 .36 6.06 3.96 .86 .88 .11 

107 Hon-18 Bt2 170 64.36 13.98 5.41 1.01 6.50 4.27 .80 .73 .11 

108 Hon-18 2BCt 190 61.23 14.38 5.40 1.44 6.63 4.59 .70 .69 .11 

109 Hon-18 3BCt 240 61.26 14.33 5.47 1.43 6.63 4.26 .74 .71 .12 

110 Hon-18 4BCt 300 58.60 14.85 6.87 3.10 7.72 4.12 .75 .76 .17 

111 Hon-19 Apl 7 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

123 Hon-20 Apl 11 

124 Hon-20 Ap2 30 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 

G104 Soil Chronosequences in the Western United States 
Supplementary table 6, part 2. Total chemical analyses of the 20-50 J.Lm fraction by X-ray fluorescence for major 

oxides-Continued 

Basal 

Sample Profile Horizon depth Si02 Al20 3 Fe20 3 MgO CaO Na20 K20 Ti02 P20s MnO 

number number (em) 

Lower member of the Riverbank Formation, 250 kaa-Continued 

128 Hon-20 2BCtl 223 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 80.01 7.69 4.67 0.27 1.68 0.73 1.18 1.65 0.09 

132 Hon-21 AB 33 80.47 8.50 5.12 .40 1.83 1.06 1.19 1.70 .10 

133 Hon-21 BA 46 79.64 8.38 5.14 .43 1.93 1.19 1.16 1.71 .10 

134 Hon-21 Btl 71 82.72 7.26 4.58 .25 .77 .48 1.31 1.72 .08 

135 Hon-21 Bt2 93 85.90 6.70 4.30 .15 .18 .19 1.38 1.66 .06 

136 Hon-21 Bt3 119 85.30 7.05 4.92 .23 .10 .38 1.34 1.74 .60 

137 Hon-21 Bt4 148 85.28 6.75 4.16 .25 .18 .34 1.40 1.69 .60 

138 Hon-21 2Bt1 197 81.86 7.89 5.46 .30 .32 .52 1.48 1.62 .60 

139 Hon-21 2Bt2 274 67.06 14.53 8.50 .32 1.46 1.28 1.25 1.26 .70 

140 Hon-21 2BC 315 62.03 15.51 9.17 .37 3.95 1.80 1.05 .96 .90 

141 Hon-21 3BC 473 57.68 16.16 8.17 .70 7.51 3.80 .78 .74 .12 

142 Hon-21 c 1300 59.01 15.61 7.14 2.13 7.19 4.89 .66 1.14 .18 

143 Hon-22 A 23 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Bt1 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCt1 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 59.43 14.71 6.76 2.91 7.87 4.48 .57 1.23 .15 

156 Hon-72 Cn 0 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G1 05 
Supplementary table 6, part 3. Total chemical analyses of the 2-20 j.Lm fraction by X-ray fluorescence for 

trace elements 

[All values in parts per million. Analyst: A.J. Busacca] 

Dasal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Holocene alluvium, 0.6 ka 

1 Hon-1 A 12 

2 Hon-1 2A1 16 

3 Hon-1 2A2 25 

4 Hon-1 2AC 49 

5 Hon-1 2C 85 

6 Hon-1 3C1 95 

7 Hon-1 3C2 122 

8 Hon-1 4B1b 140 

9 Hon-1 4B2b 170 

10 Hon-2 A1 4 

11 Hon-2 A2 32 

12 Hon-2 c 61 

13 Hon-2 2C 92 

14 Hon-2 3C 103 

15 Hon-2 4B2tb 130 

16 Hon-3 A1 4 

17 Hon-3 A2 16 

18 Hon-3 AC 31 

19 Hon-3 c 54 

20 Hon-3 2C 78 

21 Hon-4 c 17 192 84 79 139 30 196 11 151 

22 Hon-4 2A 32 198 83 86 146 31 185 10 150 

23 Hon-4 2AC 49 184 80 69 120 23 183 9 146 

24 Hon-4 2C 86 186 86 80 128 30 190 11 151 

25 Hon-4 3C1 113 202 77 86 127 28 194 10 154 

26 Hon-4 3C2 147 193 83 77 119 27 193 10 163 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 APl 13 167 71 63 112 31 190 8 163 

28 Hon-5 AP2 23 169 73 67 117 25 185 8 167 

29 Hon-5 BA 54 157 64 75 109 27 189 9 166 

30 Hon-5 Bw1 88 175 92 96 122 22 175 9 173 

31 Hon-5 Bw2 102 198 91 88 110 21 183 8 167 

32 Hon-5 BC1 141 196 93 83 113 20 183 9 164 

33 Hon-5 BC2 157 180 89 82 113 23 187 8 167 

34 Hon-6 AP1 10 

35 Hon-6 AP2 22 

36 Hon-6 BA 43 

37 Hon-6 Bw1 91 

38 Hon-6 Bw2 118 

39 Hon-6 BC1 157 

40 Hon-6 BC2 184 

41 Hon-7 AP1 8 

42 Hon-7 AP2 30 

G106 Soil Chronosequences in the Western United States 
Supplementary table 6, part 3. Total chemical analyses of the 2-20 J..Lm fraction by X-ray fluorescence for 

trace elements- Continued 

Basal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Upper member of tbe Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 

44 Hon-7 Bwl 88 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 API 7 

52 Hon-8 AP2 34 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 

55 Hon-8 Bw2 126 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 

58 Hon-8 2Cox 390 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 241 212 92 146 73 224 10 147 

60 Hon-10 BA 40 275 280 90 130 76 207 10 148 

61 Hon-10 Btl 86 283 286 89 124 79 205 10 145 

62 Hon-10 Bt2 132 285 269 83 121 75 211 10 144 

63 Hon-10 BC 150 278 260 82 125 72 235 9 140 

64 Hon-10 c 205 299 278 85 127 68 237 9 137 

65 Hon-10 2C 225 252 256 86 111 49 243 9 130 

66 Hon-11 Ap 18 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 

70 Hon-11 BC 145 

71 Hon-11 c 179 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2DCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G107 
Supplementary table 6, part 3. Total chemical analyses of the 2-20 J..Lm fraction by X-ray fluorescence for 

trace elements-Continued 

Basal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

85 Hon-14 Ap 28 151 67 57 90 56 168 7 196 

86 Hon-14 BA 39 163 73 60 70 55 164 7 198 

87 Hon-14 BAtl 59 163 79 62 74 56 163 10 201 

88 Hon-14 BAt2 76 158 83 61 81 55 151 12 193 

89 Hon-14 Btl 111 149 73 59 72 37 170 9 175 

90 Hon-14 Bt2 126 179 72 62 77 38 187 6 159 

91 Hon-14 2BCtl 150 202 94 83 102 21 172 7 122 

92 Hon-14 2BCt2 200 176 92 80 101 19 168 5 116 

93 Hon-14 2BCt3 260 175 98 88 120 23 161 7 107 

94 Hon-14 2CB 320 205 108 96 121 23 159 5 111 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 

97 Hon-17 BA 76 

98 Hon-17 Btl 100 

99 Hon-17 Bt2 160 

100 Hon-17 2BCt 201 

101 Hon-17 3BCt 208 

102 Hon-17 4BCt 295 

103 Hon-18 Apl 19 153 65 65 91 70 197 8 176 

104 Hon-18 Ap2 30 172 84 73 90 72 199 8 181 

105 Hon-18 BA 90 171 78 72 86 69 192 8 174 

106 Hon-18 Btl 113 167 80 66 77 48 188 6 167 

107 Hon-18 Bt2 170 178 78 73 92 23 195 6 129 

108 Hon-18 2BCt 190 169 75 68 83 18 196 5 116 

109 Hon-18 3BCt 240 164 84 69 85 25 191 6 128 

110 Hon-18 4BCt 300 192 93 80 110 28 179 8 115 

111 Hon-19 Apl 7 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

123 Hon-20 Apl 11 

124 Hon-20 Ap2 30 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 

128 Hon-20 2BCtl 223 

G108 Soil Chronosequences in the Western United States 
Supplementary table 6, part 3. Total chemical analyses of the 2-20 JJ.m fraction by X-ray fluorescence for 

trace elements-Continued 

Basal 

. Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Lower member of the Riverbank Formation, 250 ka-Continued 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 190 82 87 90 77 78 13 262 

132 Hon-21 AB 33 209 79 82 78 76 73 13 263 

133 Hon-21 BA 46 211 80 79 74 79 82 11 274 

134 Hon-21 Btl 71 200 86 75 69 78 46 15 278 

135 Hon-21 Bt2 93 228 115 62 75 64 31 11 255 

136 Hon-21 Bt3 119 181 101 63 67 57 25 10 246 

137 Hon-21 Bt4 148 197 89 71 79 55 23 10 247 

138 Hon-21 2Btl 197 210 88 64 53 43 20 7 214 

139 Hon-21 2Bt2 274 208 92 76 56 32 29 8 162 

140 Hon-21 2BC 315 199 88 78 69 39 70 7 167 

141 Hon-21 3BC 473 182 66 85 84 31 167 5 120 

142 Hon-21 c 1300 173 84 93 169 25 187 9 128 

143 Hon-22 A 23 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Btl 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCt1 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 150 73 71 124 24 209 10 137 

156 Hon-72 Cn 0 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G1 09 
Supplementary table 6, part 4. Total chemical analyses of the 20-50 jim fraction by X-ray fluorescence 

for trace elements 

[All values in parts per million. Analyst: A.J. Busacca] 

Basal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Holocene alluvium, 0.6 ka 

1 Hon-1 A 12 

2 Hon-1 2Al 16 

3 Hon-1 2A2 25 

4 Hon-1 2AC 49 

5 Hon-1 2C 85 

6 Hon-1 3Cl 95 

7 Hon-1 3C2 122 

8 Hon-1 4Blb 140 

9 Hon-1 4B2b 170 

10 Hon-2 Al 4 

11 Hon-2 A2 32 

12 Hon-2 c 61 

13 Hon-2 2C 92 

14 Hon-2 3C 103 

15 Hon-2 4B2tb 130 

16 Hon-3 Al 4 

17 Hon-3 A2 16 

18 Hon-3 AC 31 

19 Hon-3 c 54 

20 Hon-3 2C 78 

21 Hon-4 c 17 163 29 43 62 12 272 6 296 

22 Hon-4 2A 32 143 28 45 69 12 282 7 285 

23 Hon-4 2AC 49 147 24 40 61 14 278 7 311 

24 Hon-4 2C 86 146 41 42 54 12 274 8 288 

25 Hon-4 3Cl 113 138 29 43 56 13 287 8 378 

26 Hon-4 3C2 147 136 21 45 57 12 298 6 416 

Upper member of the Modesto Formation, 10 ika 

27 Hon-5 APl 13 125 32 34 48 H 257 5 255 

28 Hon-5 AP2 23 115 24 38 46 9 255 7 249 

29 Hon-5 BA 54 152 32 36 47 10 260 6 268 

30 Hon-5 Bwl 88 137 24 46 60 10 272 5 276 

31 Hon-5 Bw2 102 126 22 39 49 11 269 4 299 

32 Hon-5 BCl 141 156 37 39 48 10 247 7 279 

33 Hon-5 BC2 180 148 20 43 51 8 269 4 282 

34 Hon-6 APl 10 

35 Hon-6 AP2 22 

36 Hon-6 BA 43 

37 Hon-6 Bwl 91 

38 Hon-6 Bw2 118 

39 Hon-6 BCl 157 

40 Hon-6 BC2 184 

41 Hon-7 APl 8 

42 Hon-7 AP2 30 

G110 Soil Chronosequences in the Western United States 
Supplementary table 6, part 4. Total chemical analyses of the 20-50 J.Lm fraction by X-ray fluorescence 

for trace elements-Continued 

Basal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Upper member of tbe Modesto Formation, 10 ka-Continued 

43 Hon-7 BA 54 

44 Hon-7 Bwl 88 

45 Hon-7 Bw2 118 

46 Hon-7 BC 180 

47 Hon-7 2BC 230 

48 Hon-7 3Cox 290 

49 Hon-7 4Cox 340 

50 Hon-7 4Cn 370 

51 Hon-8 API 7 

52 Hon-8 AP2 34 

53 Hon-8 BA 57 

54 Hon-8 Bwl 90 

55 Hon-8 Bw2 126 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 

58 Hon-8 2Cox 390 

Lower member of the Modesto Formation, 40 ka 

59 Hon-10 Ap 22 316 ~7 46 77 26 360 9 281 

60 Hon-10 BA 40 365 133 48 81 27 324 9 280 

61 Hon-10 Btl 86 376 133 51 72 26 332 9 292 

62 Hon-10 Bt2 132 356 135 56 74 27 332 8 263 

63 Hon-10 Be· 150 331 125 53 76 26 356 8 263 

64 Hon-10 c 205 351 139 56 77 29 365 8 275 

65 Hon-10 2C 225 271 137 57 82 26 351 9 237 

66 Hon-11 Ap 18 

67 Hon-11 BA 45 

68 Hon-11 Btl 94 

69 Hon-11 'Bt2 125 

70 Hon-11 BC 145 

71 Hon-11 c 179 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCt1 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G111 
Supplementary table 6, part 4. Total chemical analyses of the 20-50 1-Lm fraction by X-ray fluorescence 

for trace elements-Continued 

Basal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

85 Hon-14 Ap 28 175 11 35 47 21 255 5 414 

86 Hon-14 BA 39 179 11 36 29 21 254 6 423 

87 Hon-14 BAtl 59 196 14 37 36 22 255 7 431 

88 Hon-14 BAt2 76 199 13 41 30 21 250 5 399 

89 Hon-14 Btl 111 171 15 43 34 15 260 5 370 

90 Hon-14 Bt2 126 184 12 40 30 16 279 6 348 

91 Hon-14 2BCtl 150 206 22 44 41 11 275 3 321 

92 Hon-14 2BCt2 200 174 29 45 42 10 262 3 278 

93 Hon-14 2BCt3 260 170 30 46 47 12 268 4 313 

94 Hon-14 2CB 320 212 30 51 48 12 272 5 322 

Lower member of the Riverbank Formation, 250 ka 

95 Hon-17 Apl 18 

96 Hon-17 Ap2 24 

97 Hon-17 BA 76 

98 Hon-17 Btl 100 

99 Hon-17 Bt2 160 

100 Hon-17 2BCt 201 

101 Hon-17 3BCt 208 

102 Hon-17 4BCt 295 

103 Hon-18 Apl -19 195 14 35 32 21 276 6 404 

104 Hon-18 Ap2 30 180 7 31 27 20 273 5 405 

105 Hon-18 BA 90 199 13 39 32 22 278 7 424 

106 Hon-18 Btl 113 203 9 37 27 19 264 4 372 

107 Hon-18 Bt2 170 143 12 35 .30 13 278 3 310 

108 Hon-18 2BCt 190 147 17 39 28 10 282 4 264 

109 Hon-18 3BCt 240 125 17 39 30 13 281 3 301 

110 Hon-18 4BCt 300 217 30 49 44 15 288 5 332 

111 Hon-19 Apl 7 

112 Hon-19 Ap2 24 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

115 Hon-19 Bt2 126 

116 Hon-19 Bt3 176 

117 Hon-19 BCt 218 

118 Hon-19 2BCtl 246 

119 Hon-19 2BCt2 268 

120 Hon-19 2BCt3 300 

121 Hon-19 3Cox 320 

122 Hon-19 3Cox 410 

123 Hon-20 Apl 11 

124 Hon-20 Ap2 30 

125 Hon-20 BA 60 

126 Hon-20 Btl 114 

127 Hon-20 Bt2 191 

128 Hon-20 2BCtl 223 

G112 Soil Chronosequences in the Western United States 
Supplementary table 6, part 4. Total chemical analyses of the 20-50 fl.m fraction by X-ray fluorescence 

for trace elements-Continued 

Basal 

Sample Profile Horizon depth Cr Ni Cu Zn Rb Sr Nb Zr 

number number (em) 

Lower member of the Riverbank Formation, 250 ka-Continued 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 277 6 39 34 25 93 9 843 

132 Hon-21 AB 33 329 14 41 41 26 99 9 797 

133 Hon-21 BA 46 320 12 40 39 24 103 7 784 

134 Hon-21 Btl 71 333 10 45 40 27 55 9 790 

135 Hon-21 Bt2 93 257 7 45 34 26 26 9 828 

136 Hon-21 Bt3 119 324 35 46 36 23 23 8 947 

137 Hon-21 Bt4 148 301 5 47 41 23 23 7 920 

138 Hon-21 2Btl 197 276 7 50 34 23 25 6 906 

139 Hon-21 2Bt2 274 224 23 66 I 39 23 72 4 625 

140 Hon-21 2BC 315 160 24 61 31 21 170 3 459 

141 Hon-21 3BC 473 157 8 65 42 15 314 6 300 

142 Hon-21 c 1300 173 15 43 43 12 302 6 260 

143 Hon-22 A 23 

144 Hon-22 AB 43 

145 Hon-22 BA 59 

146 Hon-22 Btl 89 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Bt1 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCt1 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 138 28 32 41 10 310 5 262 

156 Hon-72 Cn 0 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G113 
9 Supplementary table 7, part 1. Total chemical analyses of the fine (<50 f.Lm) fraction by instrumental neutron activation, elements Ba to Mn .... 

~ [Fe and K values in weight percent; all other values in.parts per million. Analysts: J. Budalm, D.M. McKown, and R. Knight] 

II) 

~ Basal 

n Sample Profile Horizon depth Ba Ce Co Cr Cs Dy Eu Fe Gd Hf K La Lu Mn =r 

... number number (em) 0 

::::J 

0 

Ill 

I'D 

.Q 

c: Holocene alluvium, 0.6 ka I'D 

::::J 

n 

~ 1 Hon-1 A 12 

:r 2 Hon-1 2Al 16 ;. 3 Hon-1 2A2 25 213 27.0 26.8 118 0.902 ·4.83 1.29 7.44 5.00 4.28 0.57 12.8 0.486 1400 I'D 

:; 

I'D 4 Hon-1 2AC 49 

~ 5 Hon-1 2C 85 252 30.5 31.6 113 0.912 5.18 1.39 8.21 5.20 4.36 0.50 13.8 0.532 1490 I'D 

... 6 Hon-1 3C1 95 ::::J 

c:: 7 Hon-1 3C2 122 s, 

I'D 8 Hon-1 4B1b 140 Q. 

~ 9 Hon-1 4B2b 170 ell 

;-

Ill 10 Hon-2 Al 4 

11 Hon-2 A2 32 246 30.7 29.8 109 0.871 5.41 1.33 7.72 6.12 3.97 0.50 13.2 0.521 1450 

12 Hon-2 c 61 

13 Hon-2 2C 92 265 32.9 34.3 113 0.945 5.45 1.39 7.81 5.30 4.95 0.50 15.4 0.556 1560 

14 Hon-2 3C 103 

15 Hon-2 4B2tb 130 

16 Hon-3 Al 4 

17 Hon-3 A2 16 250 25.4 27.2 101 0.850 4.91 1.34 7.10 4.90 3.87 0.76 12.8 0.501 1240 

18 Hon-3 AC 31 

19 Hon-3 c 54 252 34.2 36.5 114 0.926 5.57 1.44 8.02 5.78 4.74 0.50 15.1 0.565 1800 

20 Hon-3 2C 78 

21 Hon-4 c 17 

22 Hon-4 2A 32 I 232 28.7 27.2 118 0.926 4.89 1.34 7.66 5.21 4.29 0.55 12.9 0.499 1390 

23 Hon-4 2AC 49 

24 Hon-4 2C 86 267 28.7 30.7 116 0.958 5.75 1.43 7.95 - 4.68 0.59 13.5 0.577 1590 

25 Hon-4 3C1 113 

26 Hon-4 3C2 147 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 API 13 

28 Hon-5 AP2 23 234 27.3 30.0 107 1.16 5.65 1.41 7.81 5.64 3.81 0.50 12.2 0.553 1460 
Supplementary table 7, part 1. Total chemical analyses of the fine (<50 ~m) fraction by instrumental neutron activation, elements Ba to Mn-Continued 

Basal 

Sample Profile Horizon depth Ba Ce Co Cr Cs Dy Eu Fe Gd Hf K La Lu Mn 

number number (em) 

Upper member of tbe Modesto Formation, 10 ka-Continued 

29 Hon-5 BA 54 

30 Hon-5 Bwl 88 190 25.5 35.7 117 1.15 5.74 1.45 8.20 6.15 3.93 0.50 12.2 0.573 1580 

31 Hon-5 Bw2 102 

32 Hon-5 BCl 141 

33 Hon-5 BC2 180 

,.... 

~ ~ 34 Hon-6 APl 10 

n 

~ 35 Hon-6 AP2 22 220 24.4 29.2 106 1.17 5.54 1.37 7.70 5.22 ,3.80 0.50 12.0 0.541 1390 :I 

0 36 Hon-6 BA 43 N 

0 37 Hon-6 Bwl 91 214 23.3 30.2 110 0.928 5.19 1.40 7.10 5.15 4.27 0.50 11.6 0.552 1410 ;:;· 

~ 38 Hon-6 Bw2 118 ~ 

~ 39 Hon-6 BCl 157 

ciQ" 

~ 40 Hon-6 BC2 184 I» 

"'C 

::r 

"< 41 Hon-7 APl 8 0 

- 42 Hon-7 AP2 30 258 27.9 28.5 117 1.33 5.35 1.41 7.47 4.47 0.50 13.1 0.551 1550 :r - ~ 43 Hon-7 BA 54 "TT 

44 Hon-7 Bwl 88 246 26.7 36.4 126 ~ 

I» 1.38 6.30 1.47 7.82 - 4.30 0.54 13.3 0.579 1750 

:r 

~ 45 Hon-7 Bw2 118 ~ 46 Hon-7 BC 180 I» 

:I 

Q. 47 Hon-7 2BC 230 -< 

c 48 Hon-7 3Cox 290 a" 49 Hon-7 4Cox 340 I» 

;:IC 

<" 50 Hon-7 4Cn 370 ~ 

~ 

> 51 Hon-8 APl 7 ~ 

~ 

~ 52 Hon-8 AP2 34 243 31.5 29.7 125 1.42 5.08 1.49 7.90 5.44 4.80 0.53 13.6 0.565 1540 

n 53 Hon-8 BA 57 !!.. 

g: 54 Hon-8 Bwl 90 197 27.6 35.1 127 1.38 5.50 1.49 7.73 5.10 4.33 0.50 13.0 0.569· 1670 ~ 

:I 55 Hon-8 Bw2 126 iii" 

56 Hon-8 BCl 191 

57 Hon-8 BC2 240 227 28.9 30.8 123 1.32 5.51 1.39 6.88 5.27 3.94 0.60 13.7 0.534 1580 

9 58 Hon-8 2Cox 390 

... 

1.11 
9 

... 

0'\ Supplementary table 7, part 1. Total chemical analyses of the fine (<50 1-Lm) fraction by instrumental neutron activation, elements Ba to Mn-Continued 

VI Basal 

~ Sample Profile Horizon depth Ba Ce Co Cr Cs Dy Eu Fe Gd Hf K La Lu Mn 

n number number (em) ::T 

... 

0 

::l 

0 

(I) Lower member of the Modesto Formation, 40 ka tD 

.Q 

c: 

tD 

::l 

n 59 Hon-10 Ap 22 618 40.5 24.0 251 2.98 4.45 1.23 6.13 - 4.25 1.46 22.6 0.369 1100 tD 

(I) 60 Hon-10 BA 40 

s· 61 Hon-10 Btl 86 -::T 

tD 62 Hon-10 Bt2 132 546 44.7 35.3 249 3.06 4.38 1.29 6.56 4.94 4.11 1.65 24.2 0.408 1580 

~ 63 Hon-10 BC 150 !! 64 Hon-10 c 205 610 49.0 37.3 270 3.15 4.23 1.26 6.78 - 4.37 1.37 23.9 0.416 1590 tD 

... 65 Hon-10 2C 225 ::l 

c: 

::l 

;:::;: 

tD 66 Hon-11 Ap 24 621 44.3 23.5 241 3.06 4.48 1.26 6.05 4.28 4.25 1.79 22.8 0.366 1090 Q. 

!a 67 Hon-11 BA 45 

a 68 Hon-11 Btl 94 tD 

(I) 

69 Hon-11 Bt2 125 613 49.0 36.8 245 3.11 4.81 1.39 6.88 5.07 4.28 1.48 24.4 0.423 1580 

70 Hon-11 BC 145 

71 Hon-11 c 179 616 49.1 37.9 270 3.17 4.67 1.35 6.96 5.04 4.30 1.61 24.0 0.426 1670 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 380 45.7 27.3 164 2.43 5.10 1.41 5.34 5.28 6.14 1.05 18.4 0.538 1590 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 192 14.8 15.1 165 1.60 - 1.01 7.30 3.44 2.95 0.532 11.9 0.411 468 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

85 Hon-14 Ap 28 383 45.6 28.2 167 2.44 5.69 1.47 5.54 5.26 5.93 1.08 19.2 0.549 1540 

86 Hon-14 BA 39 

87 Hon-14 BAtl 59 
Supplementary table 7, part 1. Total chemical analyses of the fine (<50 J.Lm) fraction by instrumental neutron activation, elements Ba to Mn-Continued 

Basal 

Sample Profile Horizon depth Ba Ce Co Cr Cs Dy Eu Fe Gd Hf K La Lu Mn 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

88 Hon-14 BAt2 76 

89 Hon-14 Btl 111 316 30.8 36.8 160 2.83 4.42 1.10 6.99 4.63 3.98 0.876 15.2 0.451 1620 

90 Hon-14 Bt2 126 

91 Hon-14 2BCtl 150 

92 Hon-14 2BCt2 200 

93 Hon-14 2BCt3 260 ,... 94 Hon-14 2CB 320 I» 

";D 

~ 

~ 

;:, Lower member of the Riverbank Formation, 250 ka 0 

N 

0 

;::;· 95 Hon-17 Apl 18 ~ 

~ 96 Hon-17 Ap2 24 379 44.4 28.7 179 2.52 5.84 1.61 6.42 5.60 6.02 1.15 19.1 0.586 1590 

c:iCi. 

.., 97 Hon-17 BA 76 I» 

"C 98 Hon-17 Btl 100 -::r 

-< 99 Hon-17 Bt2 160 288 30.1 37.0 168 1.50 5.77 1.36 7.57 5.60 4.21 0.560 13.9 0.542 1460 0 - 100 Hon-17 2BCt 201 :T 

~ 101 Hon-17 3BCt 208 254 25.9 35.0 161 1.35 5.24 1.23 6.97 5.11 4.01 0.708 12.4 0.524 1300 .., 

~ 102 Hon-17 4BCt 295 I» 

:T 

~ .., 103 I» Hon-18 Apl 19 ;:, 

c. 104 Hon-18 Ap2 30 385 43.5 26.7 180 2.58 5.50 1.54 6.26 5.46 6.08 1.32 18.5 0.579 1490 

-< 105 Hon-18 BA 90 c::: 

r:r 

I» 106 Hon-18 Btl 113 ;:Ia <. 107 Hon-18 Bt2 170 274 30.5 35.7 172 1.29 5.65 1.37 7.49 4.77 4.01 0.615 13.3 0.538 1480 ~ 108 Hon-18 2BCt 190 ~ 

> 109 Hon-18 3BCt 240 253 24.3 32.7 172 1.40 5.25 1.26 7.47 4.99 3.73 0.556 12.6 0.561 1340 .., Hon-18 ~ 110 4BCt 300 ... ~» 

~ 

I» 

Hon-19 Apl 7 ~ 111 .., 112 Hon-19 Ap2 24 430 46.3 35.0 186 2.76 5.92 1.53 6.28 5.36 5.98 1.17 20.2 0.585 2010 :I Di. 113 Hon-19 BA 63 

114 Hon-19 Btl 91 

n 115 Hon-19 Bt2 126 ..A 

..A 116 Hon-19 Bt3 176 265 31.1 41.7 175 1.60 - 1.32 8.08 5.08 3.94 0.656 13.6 0.518 1590 ..... 
9 

... Supplementary table 7, part 1. Total chemical analyses of the fine (<50 J..Lm) fraction by instrumental neutron activation, elements Ba to Mn-Continued = 

VI Basal 

~ Sample Profile Horizon depth Ba Ce Co Cr Cs Dy Eu Fe Gd Hf K La Lu Mn 

n number number (em) '::t" 

0 ""' 

:I 

0 

II) 

nl Lower member or the Riverbank Formation, 250 ka-Continued ~ 

c 

nl 

:I 

n 117 Hon-19 BCt 218 nl 118 Hon-19 2BCtl 246 II) 

s· 119 Hon-19 2BCt2 268 ;. 

nl 120 Hon-19 2BCt3 300 

~ 121 nl Hon-19 3Cox 320 

~ 122 Hon-19 3Cox 410 nl 

:I ""' 

c: 123 Hon-20 Apl 11 :!. 

rD 124 Hon-20 Ap2 Q. 30 419 46.1 33.3 182 2.80 6.09 1.58 6.34 6.04 6.03 1.38 20.1 0.591 1870 

!a 125 Hon-20 BA 60 Dol 126 Hon-20 Btl 114 rD 

II) 127 Hon-20 Bt2 191 270 30.4 38.3 172 1.58 5.17 1.28 8.01 5.12 ' 4.15 0.760 13.4. ' 0.509 1380 

128 Hon-20 2BCtl 223 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member or the Laguna Formation, 1,600 ka 

131 Hon-21 A· 11 366 51.7 23.5 205 3.21 3.80 1.10 7.19 3.36 7.65 1.14 16.6 0.492 1100 

132 Hon-21 AB 33 

133 Hon-21 BA 46 

134 Hon-21 Btl 71 

135 Hon-21 Bt2 93 199 41.6 26.5 180 3.30 2.41 0.605 7.39 1.90 4.91 0.700 10.9 0.307 554 

136 Hon-21 Bt3 119 

137 Hon-21 Bt4 148 

138 Hon-21 2Btl 197 181 19.8 11.0 148 2.13 2.12 0.557 8.07 2.19 3.97 0.637 7.48 0.281 264 

139 Hon-21 2Bt2 274 

140 Hon-21 2BC 315 

141 Hon-21 3BC 473 

142 Hon-21 c 1300 

143 Hon-22 A 23 396 45.6 27.8 207 3.14 3.71 1.06 7.11· 3.33 7.01 1.12 15.8 0.470 1390 

144 Hon-22 AB 43 

145 Hon-22 BA 59 
Supplementary table 7, part 1. Total chemical analyses of the fine (<50 f.Lm) fraction by instrumental neutron activation, elements Ba to Mn-Continued 

Basal 

Sample Profile Horizon depth Ba Ce Co Cr Cs Dy Eu Fe Gd Hf K La Lu Mn 

number number (em) rCol 

;; 

("') Exhumed lower member of the Laguna Formation, 1,600 ka--Continued ~ 

::::s 

0 

N 

0 

r;· 146 Hon-22 Btl 89 219 38.8 27.6 173 3.52 2.33 0.517 7.36 1.80 4.84 0.657 10.9 0.300 695 ~ 147 Hon-22 Bt2 120 a 148 Hon-22 Bt3 154 - - - - - - - - - - - ~· 

Col 149 Hon-22 2Btl 207 "C 

~ 150 Hon-22 2Bt2 270 "< - - - - - 0 151 Hon-22 2BCt 342 

:r - 152 Hon-22 JBCtl 445 ~ 

"TT 153 Hon-22 3BCt2 505 ~ 

Hon-22 Col 154 c 1300 161 25.2 24.7 94.3 0.835 4.51 1.12 7.24 3.68 2.66 0.576 9.37 0.440 1050 :r 

~ 

Col Modern alluvium, 0 ka ::::s 

c. 

< 

c: 155 Hon-71 Cn 0 r::J" 

Col 156 Hon-72 Cn 0 ~ 

:;;:-

~ 

~ 

;e-

~ 

~ 

("') 

~ 

~ ~ 

::::s 

~· 

9 

...... 

1.0 
9 

I-.) 

0 Supplementary table 7, part 2. Total chemical analyses of the fine (<50 1-Lm) fraction by instrumental neutron activation, elements Nato Zr 

[Na value in weight percent; all other values in parts per million. Analysts: J. Budahn, D.M. McKown, and R. Knight] VI 

~ 

n 

:"' Basal .. Sample Profile Horizon depth Nd Rb Sb Sc Sm Sr Ta Tb Th Tm u Yb 0 Na Zr ::I 

0 number number (em) "' ~ 

..t:J 

c 

~ 

::I Holocene alluvium, 0.6 ka l"l 

~ 

"' :r 1 Hon-1 A 12 ;. 

~ 2 Hon-1 2Al 16 

~ 3 Hon-1 2A2 25 1.67 18.3 20.5 0.580 31.8 4.33 130 0.551 0.789 2.63 - 1.09 2.97 160 ~ 

~ 4 Hon-1 2AC 49 ~ 

.. 

::I 5 Hon-1 2C 85 1.38 17.7 18.2 .498 33.8 4.81 132 .636 .819 2.84 0.513 1.09 3.14 

c: 6 Hon-1 3Cl 95 ~ ~ 7 Hon-1 3C2 122 Q. 

~ 8 Hon-1 4Blb 140 I» 9 Hon-1 4B2b 170 tD 

"' 

10 Hon-2 Al 4 

11 Hon-2 A2 32 1.56 20.4 26.6 .468 33.3 4.75 136 .570 .826 2.67 - 1.17 3.52 151 

12 Hon-2 c 61 

13 Hon-2 2C 92 1.51 19.5 22.9 .606 32.7 5.11 150 .654 .833 2.93 - 1.18 3.43 156 

14 Hon-2 3C 103 

15 Hon-2 4B2tb 130 

16 Hon-3 Al 4 

17 Hon-3 A2 16 1.60 16.8 22.3 .520 31.0 4.44 150 .564 .762 2.48 - 1.03 3.06 179 

18 Hon-3 AC 31 

19 Hon-3 c 54 1.54 21.3 19.6 .440 33.8 4.94 220 .656 .944 3.00 .493 1.36 3.40 200 

20 Hon-3 2C 78 

21 Hon-4 c 17 

22 Hon-4 2A 32 1.61 19.0 24.0 .605 32.3 4.46 340 .570 .880 2.53 .457 1.16 3.00 160 

23 Hon-4 2AC 49 

24 Hon-4 2C 86 1.68 20.0 22.0 .495 33.5 4.67 178 .614 .966 2.80 - 1.20 3.65 187 

25 Hon-4 3Cl 113 - - - - - - - - - - - - - -

26 Hot:t-4 3C2 147 

Upper member of the Modesto Formation, 10 ka 

27 Hon-5 API 13 

28 Hon-5 AP2 23 1.66 18.1 10.0 .405 33.2 4.89 150 .473 .904 2.21 - 1.14 3.27 142 
Supplementary table 7, part 2. Total chemical analyses of the fine (<50 J.Lm) fraction by instrumental neutron activation, elements Nato Zr-Continued 

Basal 

Sample Profile Horizon depth Na Nd Rb Sb Sc Sm Sr Ta Tb Th Tm u Yb Zr 

number number (em) 

Upper member of the Modesto Formation, 10 ka-Continued 

29 Hon-5 BA 54 

30 Hon-5 Bwl 88 1.49 15.5 21.6 .430 36.2 4.78 150 .431 .890 2.29 - .973 3.75 135 

31 Hon-5 Bw2 102 

32 Hon-5 BCl 141 

33 Hon-5 BC2 180 

rCol 

;; 34 Hon-6 API 10 

n 35 ~ 

Hon-6 AP2 22 1.60 16.6 22.2 .359 32.9 4.68 120 .413 .860 2.12 .680 .853 3.44 123 ::I 

0 36 Hon-6 BA 43 N 

0 37 Hon-6 Bwl 91 1.95 17.2 23.7 .431 32.3 4.50 139 .448 .840 1.99 .569 .918 3.50 163 ;:;· 

38 Hon-6 Bw2 118 ~ ... 39 Hon-6 BCl 157 ~ 

ciQ" 40 Hon-6 BC2 184 ... 

Col 

"C 

~ 

'< 

0 41 Hon-7 APl 8 

- 42 Hon-7 AP2 30 1.75 17.7 30.7 .520 31.8 4.59 145 .474 .850 2.58 .546 1.08 3.52 148 :r 

~ 43 Hon-7 BA 54 ., 

~ 44 Hon-7 Bwl 88 1.71 18.7 30.3 .462 34.6 4.94 138 .520 .890 2.61 - 1.10 3.72 145 Col 

:r 45 Hon-7 Bw2 118 ~ 46 Hon-7 BC 180 Col 

::I 

Q. 47 Hon-7 2BC 230 

-< 48 Hon-7 3Cox 290 c: 

r:::r 

Col 49 Hon-7 4Cox 340 ;111:1 50 Hon-7 4Cn 370 <" 

~ 

~ 

~ 51 Hon-8 API 7 ~ 

,~» 52 Hon-8 AP2 34 1.80 20.1 32.0 .549 33.0 4.89 160 .533 .920 2.62 - 1.16 3.76 217 

n 53 Hon-8 BA 57 Col 

~ 54 Hon-8 Bwl 90 1.72 17.1 20.6 .464 34.5 4.72 110 .481 .900 2.58 .574 1.08 3.61 172 ... 

::I 55 Hon-8 Bw2 126 

i»" 56 Hon-8 BCl 191 

57 Hon-8 BC2 240 1.84 18.1 15.6 - 30.2 4.71 116 .476 .890 3.07 - .915 3.52 175 

9 58 Hon-8 2Cox 390 

~ 
~ 

""" N 

N Supplementary table 7, part 2. Total chemical analyses of the fine (<50 J..Lm) fraction by instrumental neutron activation, elements Nato Zr-Continued 

VI Basal ~ Sample Profile Horizon depth Na Nd Rb Sb Sc Sm Sr Ta Tb Th Tm u Yb Zr 

n number number (em) ::r 

"'I 

0 

:s 

0 

(I) 

~ Lower member of the Modesto Formation, 40 ka .Q 

c 

~ 

:s 

I") 

~ (I) 59 Hon-10 Ap 22 1.36 22.9 59.1 1.60 23.4 4.58 152 0.624 0.735 6.55 - 1.90 2.36 111 

:r 60 Hon-10 BA 40 

- 61 Hon-10 Btl 86 ::r 

~ 

~ 62 Hon-10 Bt2 132 1.20 24.8 51.9 .897 25.4 5.14 170 .591 .680 6.64 - 2.26 2.46 113 

!l 63 Hon-10 BC 150 ~ 

64 Hon-10 c 205 1.31 25.4 54.6 .947 25.6 5.27 163 .008 .710 7.04 2.35 2.52 144 "'I 

:s -

c 65 Hon-10 2C 225 

;-=· 

Q. 66 Hon-11 Ap 18 1.40 23.6 59.8 1.02 23.3 4.76 170 .628 .730 6.60 .326 1.96 2.31 155 ~ I» 67 Hon-11 BA 45 ;-

(I) 68 Hon-11 Btl 94 

69 Hon-11 Bt2 125 1.19 24.9 51.0 .810 26.4 5.30 161 .621 - 7.16 - 2.35 2.63 121 

70 Hon-11 BC 145 

71 Hon-11 c 179 1.34 24.1 55.0 .760 26.1 5.28 100 .606 .760 6.95 .380 2.31 2.52 106 

72 Hon-11 2C 220 

Upper member of the Riverbank Formation, 130 ka 

73 Hon-13 Ap 24 1.50 22.1 56.1 1.02 25.5 5.05 130 .559 .814 4.70 - 2.00 3.16 251 

74 Hon-13 BA 33 

75 Hon-13 BAtl 50 

76 Hon-13 BAt2 62 

77 Hon-13 Btl 86 

78 Hon-13 Bt2 102 1.14 13.9 10.0 .580 34.8 3.50 100 .310 .571 3.30 .429 1.19 2.55 

79 Hon-13 Bt3 123 

80 Hon-13 BCt 157 

81 Hon-13 2BCtl 208 

82 Hon-13 2BCt2 245 

83 Hon-13 2BCt3 266 

84 Hon-13 2CB 301 

85 Hon-14 Ap 28 1.46 21.8 53.7 .881 26.2 5.19 100 .591 .909 4.92 .519 2.07 3.40 202 

86 Hon-14 BA 39 
Supplementary table 7, part 2. Total chemical analyses of the fine (<50 J.Lm) fraction by instrumental neutron activation, elements Nato Zr-Continued 

Basal 

Sample Profile Horizon depth Na Nd Rb Sb sc Sm Sr Ta Tb Th Tm u Yb Zr 

number number (em) 

Upper member of the Riverbank Formation, 130 ka-Continued 

87 Hon-14 BAtl 59 

88 Hon-14 BAt2 76 

89 Hon-14 Btl 111 1.01 14.3 42.3 .720 33.4 3.98 - .463 .700 4.44 .560 1.48 2.70 156 

90 Hon-14 Bt2 126 

91 Hon-14 2BCtl 150 

92 Hon-14 2BCt2 200 

r- 93 Hon-14 2BCt3 260 ~ I'D 94 Hon-14 2CB 320 

n 

I'D 

:::J 

0 Lower member of the Riverbank Formation, 250 ka N 

0 

;::;· 

~ 95 Hon-17 Apl 18 

~ 96 Hon-17 Ap2 24 1.24 24.0 60.8 1.13 31.6 5.49 170 .503 .942 4.74 .647 1.94 3.66 253 ~· 

Col 97 Hon-17 BA 76 -c 98 Hon-17 Btl 100 ':T' 

"< 99 Hon-17 Bt2 160 1.25 19.6 27.8 .. 726 37.5 100 .335 .894 3.30 .623 1.44 3.42 141 0 -

- 100 Hon-17 2BCt 201 g. 

I'D 101 Hon-17 3BCt 208 1.48 16.4 28.0 .775 34.7 4.24 100 .316 .803 3.16 .548 1.06 3.19 155 "TT 

102 Hon-17 4BCt 295 I'D 

Col 

g. 

I'D 

~ 

Col 103 Hon-18 Apl 19 :::J 

c. 104 Hon-18 Ap2 30 1.26 24.6 62.1 .969 30.9 5.49 100 .519 .900 4.47 - 2.16 3.65 240 -< 

c: 105 Hon-18 BA 90 r:::r 106 Hon-18 Btl 113 Col 

;Ia 107 Hon-18 Bt2 170 1.45 19.5 23.0 .688 38.2 4.88 .323 .866 3.13 1.20 3.42 160 <" - - I'D 

~ 108 Hon-18 2BCt 190 

~ 109 Hon-18 3BCt 240 1.46 19.5 26.8 .666 36.5 4.54 160 .316 .884 3.11 .56~ .915 3.47 140 I'D 

!J 110 Hon-18 4BCt 300 

n 

2!.. 

~ 111 Hon-19 Apl 7 ~ 

:::J 112 Hon-19 Ap2 24 1.14 24.0 76.1 .745 29.5 5.57 100 .586 .961 5.26 .630 2.21 3.55 223 

s.;· 

113 Hon-19 BA 63 

114 Hon-19 Btl 91 

9 115 Hon-19 Bt2 126 

1-.,J 116 Hon-19 Bt3 176 1.10 16.6 28.8 .733 37.1 4.57 100 .333 .812 3.41 .559 1.22 3.22 150 w 
9 

to.) 

~ Supplementary table 7, part 2. Total chemical analyses of the fine (<50 1-Lm) fraction by instrumental neutron activation, elements Nato Zr-Continued 

II) Basal 

& Sample Profile Horizon depth Na Nd Rb Sb Sc Sm Sr Ta Tb Th Tm u Yb Zr 

n 

~ 

number number (em) .., 

0 

:::s 

0 Lower member of the Riverbank Formation, 250 ka-Continued (I) 

nl 

..Q 

c 

nl 

:::s 

n 117 Hon-19 BCt 218 nl 

(I) 118 Hon-19 2BCtl 246 s· 

- 119 Hon-19 2BCt2 268 ~ 

nl 120 Hon-19 2BCt3 300 ~ 121 Hon-19 3Cox 320 nl 

~ 122 Hon-19 3Cox 410 ~ :::s 

c: 

:::s 123 Hon-20 Apl 11 .::. 

nl 

Q. 124 Hon-20 Ap2 30 1.19 24.5 69.5 1.05 29.9 5.62 120 0.582 0.898 5.13 - 2.12 3.73 227 

~ 125 Hon-20 BA 60 

a 

nl 126 Hon-20 Btl 114 (I) 

127 Hon-20 Bt2 191 1.15 16.7 34.7 .668 36.7 4.46 100 .348 .826 3.41 - 1.23 3.11 132 

128 Hon-20 2BCtl 223 

129 Hon-20 2BCt2 260 

130 Hon-20 2CB 283 

Exhumed lower member of the Laguna Formation, 1,600 ka 

131 Hon-21 A 11 .302 17.8 64.6 .998 27.3 3.99 100 .795 .627 6.44 .620 2.70 2.85 280 

132 Hon-21 AB 33 

133 Hon-21 BA 46 

134 Hon-21 Btl 71 

135 Hon-21 Bt2 93 .048 11.9 47.7 1.02 29.9 2.46 - .623 .359 6.23 - 2.20 1.78 169 

136 Hon-21 Bt3 119 

137 Hon-21 Bt4 148 

138 Hon-21 2Btl 197 .567 10.0 33.9 1.08 31.4 1.91 100 .423 .347 4.80 .236 1.69 1.66 120 

139 Hon-21 2Bt2 274 

140 Hon-21 2BC 315 

141 Hon-21 3BC 473 

142 Hon-21 c 1300 

143 Hon-22 A 23 .290 17.9 64.1 1.19 27.3 4.05 100 .744 .604 6.19 .450 2.63 2.94 257 

144 Hon-22 AB 43 

145 Hon-22 BA 59 
r1» 

;-

~ 

~ 

:::s 

0 

N 

0 

;;· 

~ 

2t 

~· 

I» 

"'C 

=r 

"'< 

0 

-

=- ~ 

., 

m 

=-

~ 

I» 

:::s 

Q. 

-< 

c:: 

r::r 

I» 

:;ll:j 

:;:· 

~ 

~ 

> 

~ 

~ 

~ 

2!.. 

a: 

~ 

:::s 

i»" 

9 

N 

1.11 

Supplementary table 7, part 2. Total chemical analyses of the fine (<50 Jlm) fraction by instrumental neutron activation, elements Nato Zr-Continued 

Basal 

Sample Profile Horizon depth Na Nd Rb Sb Sc Sm Sr Ta Tb Th Tm u Yb Zr 

number number (em) 

Exhumed lower member of the Laguna Formation, 1,600 ka-Continued 

146 Hon-22 Btl 89 .055 9.44 60.0 1.04 30.1 2.06 - .628 .354 6.42 .254 2.28 1.62 124 

147 Hon-22 Bt2 120 

148 Hon-22 Bt3 154 

149 Hon-22 2Btl 207 

150 Hon-22 2Bt2 270 

151 Hon-22 2BCt 342 

152 Hon-22 3BCtl 445 

153 Hon-22 3BCt2 505 

154 Hon-22 c 1300 1.39 12.6 20.4 .453 37.8 3.46 138 .437 .685 2.52 .487 .880 2.61 120 

Modern alluvium, 0 ka 

155 Hon-71 Cn 0 

156 Hon-72 Cn 0 
Supplementary table 8. Calculated values of the Soil Development Index 

[ill is horizon index; PI is proflle index. Analyst, A. J. Busacca) 

Basal Basal Basal 

Horizon depth HI Horizon depth Hi Horizon depth HI 

(em) (em) (em) 

Profile: HON-1 Profile: HON-2 Profile: HON-3 

A 12 0.172 A 4 0.158 AI 4 0.128 

2Al 16 .136 A2 32 .153 A2 16 .131 

2A2 25 .179 c 61 .090 AC 31 .131 

2AC 49 .137 2C 92 .080 c 54 .053 

2C 85 .117 3C 103 .113 2C 78 .048 

3Cl 95 .119 

3C2 122 .122 

PI 16.22 PI 11.23 PI = 6.42 

PISS em 11.73 PI92 em 9.99 

Profile: HON-4 Summary: HON-1, -2, -3, -4 

c 17 0.088 x = 12.32 

2A 32 .170 full depth 

2AC 49 .101 cr 4.50 

2C 86 .112 ev 36.5 pet 

3Cl 113 .103 

3C2 147 .080 X = aubcqual 9.51 

depths 

PI 15.40 cr 2.22 

p~6em 9.89 ev 23.4 pet 

Profile: HON-5 Profile: HON-6 Profile: HON-7 

Apl 13 .181 Ap1 10 .177 Ap1 8 .153 

Ap2 23 .208 Ap2 22 .158 Ap2 30 .153 

BA 54 .203 BA 43 .211 BA 54 .200 

Bw1 88 .216 Bwl 91 .267 Bw1 88 .237 

Bw2 102 .258 Bw2 118 .242 Bw2 118 .236 

BC1 141 .234 BC1 157 .240 BC 180 .229 

BC2 180 .204 BC2 184 .214 2BC 230 .116 

PI 37.73 PI 42.45 PI 44.53 

PI180 em = 38.71 

Profile: HON-8 Summary: HON-5, -6, -7, -8 

Ap1 7 .151 x = 44.72 

Ap2 34 .151 full depth 

BA 57 .259 cr 6.91 

Bwl 90 .273 ev 15.5 pet 

Bw2 126 .264 x 41.5 

BCl 191 .243 aubcqual 

BC2 240 .179 clcplh 

cr 3.51 

PI 54.17 ev 8.5 pet 

Pit9t c:m = 45.41 

Profile: HON-9 Summary: HON-9, -10, -11 

Apl 16 .152 x 50.52 

Ap2 25 .168 aubcqual 

BAtl 42 .218 deplh 

BAt2 80 .407 cr 5.14 

2Bqkrnl 99 .384 ev 10.2 pet 

2Bqkm2 113 .384 

2BCqm 137 .369 

3BCt 153 .237 

3C 198 .176 

PI 56.3 

Profile: HON-10 Profile: HON-11 Summary: HON-10,-11 

Ap 22 .233 Ap 18 .208 x = 47.65 

BA 40 .212 BA 45 .251 full depth 

Btl 86 .324 Btl 94 .277 cr 1.68 

Bt2 132 .344 Bt2 125 .368 ev 3.5 cftt 

BC 150 .208 BC 145 .230 x 45. 1 

c 205 .073 c 179 .074 subcqual 

2C 225 .069 2C 220 .094 dl:p1h 

cr 3.44 

PI 48.82 PI = 46.45 ev 7.6 pet 

Plzos em = 47.44 PII79 em = 42.58 

G126 Soil Chronosequences in the Western United States 
Supplementary table 8. Calculated values of the Soil Development Index-Continued 

Basal Basal Basal 

Horizon depth HI Horizon depth Hi Horizon depth HI 

(em) (em) (em) 

Profile: HON-13 Proftle: HON-14 Summary: HON-13,-14 

Ap 24 .133 Ap 28 .129 xfulldcpth = 101.52 

BA 33 .169 BA 39 .182 

BAtl 50 .238 BAtl 59 .270 0' 1.28 

BAt2 62 .426 BAt2 76 .352 ev 1.3 pet 

Btl 86 .518 Btl 111 .522 

Bt2 102 .490 Bt2 126 .415 

Bt3 123 .473 2BCtl 150 .483 

BCt 157 .408 2BCt2 200 .349 

2BCtl 208 .345 2BCt3 260 .292 

28Ct2 245 .302 2CB 320 .239 

38Ct3 266 .295 

3BC 301 .220 PI 102.42 

PI 100.61 

Profile: HON-17 Proflie: HON-18 Profile: HON-19 

Apt 18 .236 Apl 19 .304 Apl 7 .189 

Ap2 24 .233 Ap2 30 .248 Ap2 24 .213 

BA 76 .356 BA 90 .365 BA . 63 .330 

Btl 100 .437 Btl 113 .429 Btl 91 .346 

Bt2 160 .493 Bt2 170 .491 Bt2 126 .468 

28Ct 201 .436 2BCt 190 .412 Bt3 176 .489 

38Ct 208 .328 3BCt 240 .394 BCt 218 .378 

48Ct 295 .346 4BCt 300 265 2BCtl 246 .312 

2BCt2 268 .315 

PI 114.48 PI 112.08 2BCt3 300 .174 

PI 105.41 

Profile: HON-20 Summary: HON-17, -18, -19, -20 

Apl 11 .186 x 107.84 

Ap2 30 .216 0' 6.76 

BA 60 .277 ev 6.3 pet 

Btl 114 .337 

Bt2 191 .511 

2BCtl 223 .382 

2BCt2 260 .293 

2CB 283 .194 

PI 99.52 

Profile: HON-21 Proftle: HON-22 Summary: HON-21,-22 

A 11 .276 A 23 .347 x 223.36 

AB 33 .350 AB 43 .348 0' 6.54 

BA 46 .394 BA 59 .460 ev 2.9 pet 

Btl 71 .572 Btl 89 .576 

Bt2 93 .646 Bt2 120 .617 

Bt3 119 .638 Bt3 154 .599 

Bt4 148 .651 2Btl 207 .584 

2Bt1 197 .605 2Bt2 270 .501 

2Bt2 274 .523 2BCt 342 .410 

2BC 315 .446 3BCtl 445 .338 

3BC 473 .331 3BCt2 505 .341 

PI 220.29 PI 226.43 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G127 · 
Supplementary table 9, part 1. Radiocarbon ages 

[Analyst, Beta Analytic] 

Laboratory C-14 age 

Sample number Location (yr B.P.)±lcr 

H00-21 Beta-1649 SE1

/4 sec. 23, T. 17 N., R. 3 E. 1,625±90 

400 rn due west of State Highway 

70, in northeast bank of North 

Honcut Creek, at depth of 2.5 rn. 

HON-4 Beta-1650 Sec. 18, T. 17 N., R. 4 E.; 700 rn 625±60 

east of Western Pacific Railroad, 

south bank of southernmost channel 

of South Honcut Creek, at depth 

of 1.2 rn in C horizon of soil 

profile HON-4. 

H00-25A Beta-1651 NE1/4 sec. 15, T. 17 N., R. 4 E.; 450±45 

70 rn east of westernmost high 

power line, in north bank of 

Honcut Creek at a depth of 

2.1 rn. 

LR0-2 Beta-1652 400 rn west-northwest of center 1,110±95 

of sec. 23, T. 17 N., R. 4 E.; 

east bank of north-south reach 

of South Honcut Creek, 6 rn 

south of old east-west fenceline 

at a depth of 96 ern. 

H00-25B Beta-1653 Same as H00-25A, at depth of 595±70 

40 ern. 

H00-19-1 Beta-1654 SE1/4SE1/4 sec. 16, T. 17 N., R. 4 E., 1,045±95 

south bank of North Honcut Creek, 

where creek turns from south to 

southwest, at a depth of 2.8 rn. 

LR0-1 Beta-1655 Near southeast comer, sec. 14, 1,775±110 

T. 17 N., R. 3 E.; directly across 

the channel from H00-21, at 25 

ern depth. 

G128 Soil Chronosequences in the Western United States 
,... 

ell 

;;-

("') 

I'D 

::I 

0 

s 

;:;· 

~ 

a 

~· 

ell 

"'0 

=r 

-< 

a 

;. 

I'D 

"TI 

~ 

;. 

(I) 

~ 

ell 

::I 

Q. 

-< 

c 

aCII 

;Ia 

::::· 

(I) 

~ 

> 

~ 

~ 

("') 

2!.. 

~ ~ 

::I 

i»" 

~ t-) 

\0 

Supplementary table 9, part 2. K-Ar radiometric ages of dacite blocks from lahar of the dacite unit 

[OR0-9A,B consisted of 2 samples of fresh dacite blocks in a lahar tmit, SE1/4NE1/4 sec. 15, T. 19 N., R. 4 E., roadcut on Olive Highway at church. OR0-21 consisted of 1 sample of fresh dacite from a lahar 

unit, NW1/4NW1/4 sec. 9, T. 19 N., R. 4 E., Long Bar Road approximately 150m south of Y-spliL All ages obtained by analyses performed at the U.S. Geological Survey laboratories in Menlo Park, California 

between 1982 and 1984. Potassiwn was analyzed by S. Neil and D. Vivit by flame photometry, using lithium metaborate fusion, with lithiwn serving as an internal standard (lngamells, 1970). Argon was analyzed 

by Wendy Hillhouse by the standard isotope-dilution and mass-spectrometry techniques described by Dalrymple and Lanphere (1969). Mineral separates were prepared by D.H. Sorg. Constants used in the 

calculations are: A.E+A£=0.581xl0· 1

Dyrl, AP=4.962x1Q-11lyr1

, and 40J</K..,.al=l.l67x10·4mol/mol] 

Field 

number 

Oro-9A 

Oro-9B 

Oro-21 

Material 

analyzed 

Dacite 

Biotite 

Hornblende 

Biotite 

Hornblende 

Weight 

percent 

1.913 

7.58 

.406 

8.105 

.444 

K2 0 

a 

3.60 

.62 

.603 

.236 

.216 

Number 

of values 

4 

4 

4 

4 

4 

Argon 

•oAr rod 

(mol/g) 

8.84188x10-12 

8.71626x10-12 

3.72008x1o-n 

1.61132x10-12 

1.95173x10-12 

3.97022x1o-n 

2.06710x10-12 

100 rad 40Ar Apparent Age locality 

totai 40Ar age (Ma) (Ma) ±a lat N. long W. 

58.73 3.2 

3.2±0.1 (3 pet) 39°30'20" 121°30'52" 

27.20 3.2 

29.92 3.4 3.4±0.2 (5 pet) 

39°30'20" 121°30'52" 

4.10 2.8 2.8±0.3 (10 pet) 

6.14 3.3 3.3±0.3 (10 pet) 

20.16 3.4 3.4±0.2 (5 pet) 

39°31'21" 121°32'10" 

3.41 3.2 3.2±0.3 (10 pet) 
Supplementary table 10. Tephra correlation 

[Results based on comparison of minor- and trace-element chemistry of glass from tuff samples using similarity-coefficient analysis (Sarna-Wojcicki, 

1976); analyst, A.N. Sarna-Wojcicki] 

Sample 

BV0-5 

81F-11 

Therm-1 

Location and description 

Blue-gray subrounded pumice pebbles in a fluvially derived 

crystal-vitric matrix; collected at 4 m in backhoe pit, NE~NE~ sec. 8, 

T. 15 N., R. 5 E., Browns Valley 7Yz.-minute quadrangle. 

Sample of tuffaceous(?) silt; collected by geologists of California 

Department of Water Resources from a depth of 21 m (69 ft) 

beneath a deposit mapped as the Laguna Formation; elevation, 

186ft; Thermalito Forebay Dam at toe. SW~ sec. 10, T. 19 N., 

R. 3 E., Shippee 1Y2-minute quadrangle. 

Sample of white pumice pebbles in tuffaceous sand collected by 

a geologist of California Department of Water Resources from a 

depth of 4.6 m (15ft) beneath a deposit mapped as the lower 

member of the Riverbank Formation; elevation, 115ft; Thermalito 

Afterbay perimeter dam at toe. SW~ sec. 19, T. 19 N., R. 3 E., 

Biggs 1Y2-minute quadrangle. 

G130 Soil Chronosequences in the Western United States 

Result 

Correlated with· the Nomlaki 

Tuff Member of the Tehama 

Formation. 

Diatomaceous silt. 

Not correlated; similarity 

coefficient approx. 0.90 for 

comparison with Rockland 

ash bed; approx. 0.85-0.90 

for comparison with Nomlaki 

Tuff Member of the Tehama 

Formation. 
Supplementary table 11. Paleomagnetic determinations 

[A total of 40 samples from the four sites were collected for paleomagnetic study; analyst K.L Verosub. Each sample consisted of a pedestal of 

sediment carved in the outcrop and collected in a small plastic box. Because the purpose of the study was only to ·ascertain the magnetic-polarity 

zonation, the orientations of the samples were determined with an accuracy of only about ±5°. All the samples were subjected to at least five levels of 

alternating field demagnetization (0, 10, 20, 30 and 40 mT), and many samples were studied at intermediate and higher levels as well. After each 

demagnetization, the samfles were measured with a spinner magnetometer operating in a six-spin mode. The initial intensities of the samples ranged 

from 1.3xl0-3 to 5.6x10- emu, and the median destructive fields ranged from 10 to 30 mT. The results are shown in figure 5. Detailed stereographic 

projections arc shown in the supplementary figure. The behavior of the samples upon demagnetization indicated that the magnetic carrier was magnetite 

and that the magnetization of the samples was a detrital remanent magnetization acquired at or shortly after deposition. With three exceptions, all the 

samples showed minimal directional changes after the initial demagnetization to 10 mT. For all these samples, the direction at a representative 

demagnetization level of 20 mT is shown in the supplementary figure. For each sample, the polarity can be unambiguously determined to be either 

normal (down and northward) or reversed (up and southward). The three samples that did not have stable end points above 10 mT (queried in fig. 5) are: 

the sample above the buried soil at the Western Pacific Railroad site (site 2), the lowest sample at that site, and a sample near the base of the upper 

member of the Laguna Formation at the same site. The complete demagnetization behavior for the first sample is shown in supplementary figure B. 

Although the directions are not particularly stable, there appears to be no tendency toward a reversed direction, and so this sample has been classified as 

probably normal. The second sample (fig. C), and the third sample (fig. D), however, both show a clear progression to a reversed direction and so they 

have been classified as probably reversed] 

Site 

Feather River, site 1 

Western Pacific 

Railroad, site 2 

Meadowview Road, 

site 3 

Wyandotte Road, site 4 

location and description 

SE~ sec. 13, T. 19 N., R. 3 E. Composite section from Bluff exposure on west bank of 

Feather River; samples taken in stratigraphic succession at sites a few meters south to 80 m 

north of old railroad-bridge piers. Section sampled exposes very coarse cobble conglomerate 

of the upper member of the Laguna Formation overlying thin-bedded volcaniclastic silt and 

sand and a thin lahar belonging to the dacite unit. 

NE~ sec.31, and SE~ sec. 30, T. 19 N., R. 4 E. This is a composite section that includes 

from the top of the section to the bottom, the north face of the roadcut in Ophir Road, the 

southeast-facing sideslope of the adjacent hill, the west side of the Western Pacific Railroad 

cut, and the roadcut in Baggett-Palermo Road. This section is described on p. G26 and 

consists of the upper member of the Laguna Formation unconformably overlying volcanic 

sediment of the dacite unit 

NW~ NE~ sec. 15, T. 19 N., R. 4 E. This section exposes the Nomlaki Tuff Member of 

the Laguna Formation overlying volcanic sediment and a dacitic lahar of the dacite unit. 

The contact zone between the dacite unit and the Nomlaki Tuff Member may be gradational. 

The exposure starts at the intersection of Oro-Quincy Highway and Meadowview Road and 

extends eastward on Meadowview Road. This section is described on p. G34-G35. 

Approximately 60 m north of theE~ cor. NW~ sec. 21, T. 19 N., R. 4 E. Samples were 

taken from the east side of a roadcut on Wyandotte Road that exposes several meters of 

thin- bedded, fluvial, pumice-pebble-bearing sediment of the Nomlaki Tuff Member of the 

Laguna Formation. 

Late Cenozoic Stratigraphy of the Feather and Yuba Rivers Area, California G131 
w 

w 

N 

s 

N 

s 

E 

E 

Supplementary figure 1. Stereographic projections of data 

from paleomagnetic studies. Each point represents direction of magnetization of a single sample after demagnetization to 20 mT; crosses, data points on lower hemisphere; circles and dots, data points on upper 

hemisphere. A, Samples from Feather River (site 1) are 

crosses; from Meadowview Road (site 3), circles; from 

Wyandotte Road (site 4), dots. 8, Top eight samples from 

G132 Soil Chronosequences in the Western United States 

w 

w 

N 

.. 

. .. 

s 

N 

s 

X 

~ E 

E 

Western Pacific Railroad site (site 2), showing complete 

demagnetization behavior of queried normal sample 

above buried soil. C, Bottom two samples from Western 

Pacific Railroad site, showing complete demagnetization 

behavior of lowest sample. D, Remaining samples from 

Western Pacific Railroad site, showing complete demagnetization behavior of queried normal sample from near 

base of upper member of Laguna Formation. 

GPO 685-041 /9801 
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