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




                DESCRIPTION OF MAPPING OF QUATERNARY DEPOSITS 
                       AND LIQUEFACTION SUSCEPTIBILITY,
              NINE-COUNTY SAN FRANCISCO BAY REGION, CALIFORNIA


                                    by

       Keith L. Knudsen(1,2), Janet M. Sowers(1), Robert C. Witter(1), 
                Carl M. Wentworth(3), and Edward J. Helley(1)




                                 Part 3 of
                         Open-File Report 00-444
                                Version 1.0




                                    2000



                             Author Affiliations

                    1 - William Lettis & Associates, Inc.
                    2 - California Division of Mines and Geology, 
                    3 - U.S. Geological Survey





This report is preliminary and has not been reviewed for conformity with U.S. 
Geological Survey editorial standards or with the North American Stratigraphic 
Code. Any use of trade, product, or firm names is for descriptive purposes only 
and does not imply endorsement by the U.S. Government.



              DESCRIPTION OF MAPPING OF QUATERNARY DEPOSITS 
                    AND LIQUEFACTION SUSCEPTIBILITY,
             NINE-COUNTY SAN FRANCISCO BAY REGION, CALIFORNIA


                             TABLE OF CONTENTS

	Table of Contents					ii
	Introduction						 1
	Acknowledgments						 3
	Methods 						 4
	Results							16
		Ground water					17
		Historical liquefaction in the	        	17
 		 nine-county San Francisco Bay Region
		Liquefaction susceptibility units		19
	References						20


                                 FIGURES

   	1   The nine-county San Francisco Bay Region, 		 2
	     with major faults
   	2   Correlation of geologic map units			 5
   	3   Index map to table 3	 			11


                                 TABLES

	1   Categories of age and depositional environment	 4
	     used in Quaternary geologic mapping
	2   Correlation chart showing relations between		 7
	     the stratigraphy used in this study and the 
	     stratigraphies of previous researchers
	3   Documentation of mapping procedures and sources	 9
	     of information
	4   Criteria matrix for assigning liquefaction 		14
	     susceptibility units
	5   Preliminary liquefaction susceptibility 		18
	     assignments and evaluation of relations between 
	     mapped occurrences of liquefaction and Quaternary 
	     geologic map units


                              APPENDICES

	A.  Description of geologic units			A-1
	B.  Relation of soil series to Quaternary units		B-1
	C.  A preliminary digital compendium of ground 		C-1
	     effects associated with earthquakes in the 
	     San Francisco Bay Region


                             INTRODUCTION

A new map of Quaternary deposits and a derivative map of liquefaction 
susceptibility have been prepared for the nine-county San Francisco Bay region 
(figure 1).  The maps are in the form of a digital database, produced from 
original 1:24,000- and 1:100,000-scale geologic mapping.  These maps represent 
the first region-wide characterization of Quaternary deposits in the Bay region 
since the 1970s.  The maps provide a modern and regionally consistent treatment 
of Quaternary deposits that builds on the pioneering work of Helley and others 
(1979) and the subsequent work of Atwater (1982), Helley and others (1994) and 
Helley and Graymer (1997a and 1997b).  The Quaternary deposits map was 
originally produced with the intention of developing the derivative liquefaction
susceptibility map.  However, the Quaternary deposit map may be used for a 
variety of other purposes, including: neotectonic analyses; estimating 
earthquake shaking; as a screening tool in engineering geologic and geotechnical
evaluations; evaluation of sand and gravel resources; landscape evolution 
modeling; and regional hydrologic and hydrogeologic characterizations.  The maps
also are intended to provide baseline data for use in development of 
liquefaction hazard zone maps by the Seismic Hazard Mapping Program of the 
California Division of Mines and Geology (CDMG).  The map products of this study
are not meant to replace those zonation maps; these maps serve a different role 
by providing a regional perspective on Quaternary deposits and liquefaction 
susceptibility.


Figure 1.  The nine-county San Francisco Bay Region, with major faults.
           Modified from Perkins and others (1999)


Quaternary deposits are subdivided using two criteria: their age and their 
environment of deposition.  The age of a deposit influences its density, degree 
of cementation, ability to transmit earthquake energy, and hydraulic 
conductivity.  We use geomorphic relations, degree of soil profile development 
and erosional modification of geomorphic surfaces to evaluate the age of 
deposits.  The size, shape and arrangement of grains, hydraulic conductivity, 
and lateral continuity of deposits are a function of the environment in which 
sediment was deposited.  We use interpretation of topography and aerial 
photographs to identify landforms and relate the landforms to the environment in
which they were formed.  A material's age and environment of deposition also 
affects its likelihood of experiencing earthquake-induced liquefaction.  

Earthquake-induced ground failures owing to liquefaction have caused loss of 
life and damage to property and infrastructure in many earthquakes.  
Liquefaction is the transformation of a saturated granular material from a solid
to a liquefied state as a result of increased pore pressure and decreased 
effective stress (Youd, 1973).  Observed types of ground failure resulting from 
liquefaction can include sand boils, lateral spreads, ground settlement, ground 
cracking and ground warping (Youd and Hoose, 1978).  Observations of the effects
of large-magnitude earthquakes show that the distribution of liquefaction 
phenomena is not random; it occurs in areas underlain by loose, saturated, 
cohesionless sand, silt and gravel.  Areas susceptible to liquefaction can be 
delineated on the basis of geologic, geomorphic, and hydrologic mapping and map 
analyses (Dupr and Tinsley, 1980; Youd and Perkins, 1987; Tinsley and Holzer, 
1990; Sowers and others, 1995; Knudsen and others, 1997; Tinsley and others, 
1999).  In this study, we use the new Quaternary map (Map Sheet 1) together with
information about past liquefaction effects and estimates of ground-water levels
to produce a liquefaction susceptibility map of the San Francisco Bay region 
(Map Sheet 2).  The geologic materials most susceptible to liquefaction include 
Holocene stream channel deposits, Holocene beach deposits, and artificial fill 
overlying Bay Mud; these deposits are widely present in the region.  The 
analysis of liquefaction susceptibility is patterned after studies by Dupr and 
Tinsley (1980) and Dupr (1990) in the Monterey-Santa Cruz area, Tinsley and 
others (1985) in the Los Angeles area, Youd and Perkins (1987) in San Mateo 
County, California, Sowers and others (1995) in the northern San Francisco Bay 
area, and Knudsen and others (1997) in the central San Francisco Bay area.  
Users of the maps should recognize that the susceptibility map is not a ground 
failure map; it shows the susceptibility of materials to liquefaction.  Ground 
failures commonly accompany liquefaction, however, and may be expected in areas 
with higher susceptibility levels (Tinsley and others, 1985).  

The new Quaternary maps are an improvement over the 1970s-vintage maps of Helley
and others (1979) in that (1) much of the mapping is at a scale of 1:24,000, (2)
a detailed stratigraphic nomenclature has been developed that is based on age 
and environment of deposition, (3) a revised model of landscape evolution has 
been used, and (4) the mapping procedures and source materials used are 
documented for each 7.5-minute quadrangle.  Much of the area here presented at a
scale of 1:100,000 is being revised at a scale of 1:24,000 by William Lettis & 
Associates, Inc. (WLA), the California Division of Mines and Geology, and the 
U.S. Geological Survey for subsequent incorporation into a revised version of 
the Quaternary deposits database.  Thus, the present report is an interim 
product.  Because we will be refining existing mapping and inserting more 
detailed mapping into the database, we have not resolved all quadrangle-boundary
problems.

Use of the digital database should not violate the spatial resolution of the 
data.  Resolution higher than that of the original mapping is not present and 
enlargement of the database and maps to larger scales will not yield greater 
detail.  


                                ACKNOWLEDGMENTS

John N. Baldwin of William Lettis & Associates, Inc. and Kevin B. Clahan of the 
California Department of Conservation, Division of Mines and Geology provided 
assistance in map compilation and data analysis.  We thank Robin Grossinger of 
the San Francisco Estuary Institute and Mark DeLisle of the California Division 
of Mines and Geology for providing geomorphic and geologic data.  Additionally, 
we thank the individuals and agencies that provided access to borehole logs and 
other information on local geology, including the California Division of Mines 
and Geology; California Department of Transportation; and the Bay Area Rapid 
Transit District.  William R. Lettis and John C. Tinsley provided guidance and 
technical review.  

The Quaternary mapping and liquefaction susceptibility analyses were supported 
by the U.S. Geological Survey National Earthquake Hazards Reduction Program 
Grants #14-08-0001-G2129, 1434-94-G-2499, 1434-HQ-97-GR-03121, 99-HQ-GR-0095, by
the professional development fund of William Lettis & Associates, Inc, the 
California Department of Conservation, Division of Mines and Geology, and the 
Earthquake Hazards Program of the U.S. Geological Survey.


                                   METHODS

Quaternary deposits are mapped chiefly through the interpretation of 
1:24,000-scale topographic maps, aerial photographs, and soil surveys, by 
reference to published and unpublished geologic maps, and by field 
reconnaissance. Categories of age and environment distinguished in this study 
are listed in table 1 and shown in figure 2.


	Table 1. Categories of age and depositional environment used in 
                 Quaternary geologic mapping.

  Age (1)                             		Depositional Environment

  Material deposited by humans (a_) (2) 	Active stream channel (c)

  Modern (<150 yrs)               		Alluvial terrace (t) 

  Latest Holocene (Qh_y) (<~1000 yrs)   	Alluvial fan (f)

  Late Holocene (Qh) (<~3000 yrs)   		Alluvial fan levee (l)

  Holocene (Qh) (<10,000 yrs)               	Fine grained (distal) alluvial 
						 fan (ff)

  Latest Pleistocene to Holocene (Q)		Alluvial fan-estuary 
   (<~30,000 yrs)				 transition (fe)

  Latest Pleistocene (Qp)   			Alluvial basin and flood basin 
   (10,000 to ~30,000 yrs)			 (b, fb)

  Early to late Pleistocene (Qo) 		Alluvial floodplain (fp)
   (~30 kyrs to 1.6 myrs)   			Undifferentiated alluvial (a)
                                            	Estuary/bay (bm)
                                            	Estuary/delta (dm)
                                            	Beach (bs)
                                             	Dune (ds)
                                            	Marine terrace (mt)
                                            	Pediment (p)

Notes: 
(1) We use several age boundaries in defining map units in this study 
other than the standard Quaternary boundaries (Harland and others, 1990) to 
permit effective distinction of materials with different susceptibilities to 
liquefaction.  Thus, in the Holocene, we distinguish materials deposited within 
the past 150 years (by humans), within the past 1,000 years (latest Holocene), 
and within the past 3,000 years (late Holocene) from materials simply designated
as Holocene.  In the Pleistocene we distinguish materials less than 30 thousand 
years old (latest Pleistocene) from older ones (late to early Pleistocene), 
because these younger Pleistocene materials are more likely to liquefy.  With 
additional effort, further differentiation of Pleistocene deposits would be 
possible.  
(2) Abbreviations used in unit designations are shown in parentheses. 


Figure 2.  Correlation of geologic map units


We delineate landforms and Quaternary deposits, including stream and marine 
terraces, alluvial fans and levees, beaches, dunes, and marshes, principally 
from interpretation of topographic maps and aerial photographs.  Early 20th 
century 1:24,000-scale and 1:62,500-scale topographic maps were used to 
characterize pre-development topography and identify landforms and streams that 
have since been altered by development.  The oldest available aerial photography
was used in order to evaluate landforms prior to their modification by recent 
development.  For much of the San Francisco Bay region, the earliest aerial 
photographs are approximately 1:20,000-scale, 1939 photographs.  

Criteria used to evaluate age of deposits include landform shape and relative 
geomorphic position, cross-cutting relations and superposition, depth and extent
of erosional dissection, relative degree of soil profile-development, and 
correlation to dated deposits.  Additionally, deposits are correlated to the 
stratigraphic framework used by previous researchers (table 2).  Such previous 
studies include research in the Sacramento Valley (Helley and Harwood, 1985), 
eastern San Joaquin Valley (Marchand and Harden, 1978; Marchand and Allwardt, 
1978, 1981; Atwater, 1982; Harden, 1987), western San Joaquin Valley (Lettis 
1982, 1985; Bartow and others, 1985; Sowers and others, 1993a,b; Noller and 
others 1993), and the San Francisco Bay area (Atwater and others 1977; Helley 
and others, 1979; Atwater, 1982; Knudsen and others, 1997).  Deposits that could
not be confidently distinguished as either Holocene or latest Pleistocene are 
assigned the age designation of latest Pleistocene to Holocene.  This 
designation is also used where Holocene deposits are inferred to form a thin 
veneer over latest Pleistocene deposits.

A major challenge in this project was to map each of the one hundred sixty-six 
quadrangles in the San Francisco Bay area using consistent stratigraphy, 
nomenclature, style, and level of detail.  The maps we present are a combination
of original mapping and previous mapping that has been modified to fit our 
stratigraphy, nomenclature, and mapping style (see table 3).  In some cases the 
modifications are minor, such as changing the unit symbol for Holocene alluvial 
fan from Qhaf, used by Helley and Graymer (1997a, b), to Qhf.  In other cases 
modifications are extensive and include original mapping or revision of age 
assignments.  Table 3 and figure 3 document the origin of the mapping and the 
extent and basis for revisions or modifications for each quadrangle.  Most areas
were mapped at a scale of 1:24,000.  Areas mapped at a scale of 1:100,000 
include parts of the San Francisco, San Jose and Napa 1:100,000 quadrangles.  In
addition to showing the sources and methods used for each quadrangle, figure 3 
also shows the estimated "percent completion" of each quadrangle.  A value of 
100 percent indicates that we feel confident in the mapping and that all of the 
following methods were used in developing the map: review of previous maps, 
interpretation of landforms through analysis of topographic contours on 
7.5-minute quadrangles, inspection of stereo-paired aerial photographs, review 
of soil survey maps, and field reconnaissance.  Completion percent values of 
less than 100 percent indicate, in a relative way, the level of effort completed
to date, with 50 percent indicating that existing mapping has simply been 
reinterpreted and modified to fit the stratigraphic nomenclature used herein.  A
value of 100 percent does not indicate that the map cannot be improved, it means
that the above-listed standards for this study have been met.  

 
Table 2.  Correlation chart showing relations between the stratigraphy used 
 in this study and the stratigraphies of previous researchers.

  For each unit mapped in this study (shown in first column), the chart shows 
  how previous studies typically mapped the same unit. 

  Blank cells indicate that the unit either was not mapped, or was included in 
  another unit.

  [Lines of the table are presented here as comma-delimited records]

UNIT,"Knudsen and others, 2000 (This study)","Knudsen and others, 1997, San 
	Francisco 1:100,000","Sowers and others, 1995, 1998; Napa 
	1:100,000","Helley and Graymer, 1997a, b; Alameda & Contra Costa 
	Counties digital 7.5' quadrangles","Atwater, 1982; Sacramento, San 
	Joaquin Delta 1:24,000","Helley and others, 1994; Santa Clara Valley, 
	1:24,000","Helley and Harwood, 1985; Sacramento Valley, 
	1:62,500","Helley and others, 1979; San Francisco Bay area; 
	1:125,000","Wentworth and others, 1998; San Jose 1:100,000"

Artificial fill,af,af,af,af, , , , ,af
Artificial fill over Bay Mud,afbm, , , , , , , , 
"Artificial fill, levee",alf, , ,alf, , , , , 
Dredge spoils,ads, , , ,Qds, , , , 
Gravel quarries and percolation ponds,gq,af, ,GP, ,"PP,GP", , ,"PP,GP"
Artificial stream channel,ac, , ,Qhasc, , , , , 
Modern stream channel deposits,Qhc,Qhc, ,Qhsc, ,Qhsc,Qsc,Qhsc,Qhc
Latest Holocene alluvial fan deposits,Qhfy, , ,Qhaf1, , , , , 
Latest Holocene alluvial fan levee deposits,Qhly, , , , , , , , 
Latest Holocene stream terrace deposits,Qhty, , ,"Qhfp1,2", , , , , 
"Latest Holocene alluvial deposits, undifferentiated",Qhay, ,Qhi, , , , , , 
Latest Holocene beach sand,Qhbs, , , , , , , , 
"Late Holocene alluvial floodplain deposits, undivided",Qhfp, , , ,Qfp, , , , 
Late Holocene flood basin deposits,Qhfb, , , ,Qfb, ,Qb, , 
Holocene dune sand,Qhds,Qhs,Qhs,Qhds, , , ,Qhs, 
Holocene San Francisco Bay mud,Qhbm,Qhbm,Qhr,Qhbm, ,Qhbm, ,Qhbm,Qhbm
Holocene San Joaquin/ Sacramento Delta mud and peat,Qhdm, , ,Qhpm,Qpm, ,Qp, , 
Holocene basin deposits,Qhb,Qhb,Qhb,"Qhb, Qhbs","Qyymc, Qym",Qhb,Qb, ,Qhb
Holocene fine grained alluvial fan-estuarine complex deposits,Qhfe, , , , ,Qhbs,
	, , 
Holocene alluvial fan deposits,Qhf,Qhf,Qhf,Qhaf, ,"Qhaf, Qhfp",Qa,"Qham, 
	Qhac","Qhf, Qhfp"
"Holocene alluvial fan deposits, fine grained facies",Qhff, , , , , , ,Qhaf, 
Holocene alluvial fan levee deposits,Qhl,Qhl, ,Qhl,Ql,Qhl,Qa, ,Qh1
Holocene stream terrace deposits,Qht,Qht,Qht,Qhfp, ,Qhfp, , ,Qht
"Holocene alluvium, undifferentiated",Qha,Qha,Qha,Qhaf, , ,Qa, ,Qha
Latest Pleistocene to Holocene dune sand,Qds,Qps,Qs,Qms,Qm2e, , ,Qps, 
Latest Pleistocene to Holocene basin deposits,Qb, , , , , , , ,Qt
Latest Pleistocene to Holocene alluvial fan deposits,Qf,Qf,Qf, , , , , , 
Latest Pleistocene to Holocene alluvial fan levee deposits,Ql, , , , , , , , 
Latest Pleistocene to Holocene stream terrace deposits,Qt, ,Qt, , , , , , 
"Latest Pleistocene to Holocene alluvium, undifferentiated",Qa,Qa,Qa, , , , , 
	,Qa
Latest Pleistocene basin deposits,Qpb, , , , , , , , 
Latest Pleistocene alluvial fan deposits,Qpf,Qpf,Qpf,Qpaf,"Qm, Qch",Qpaf, , ,Qpf
Latest Pleistocene stream terrace deposits,Qpt, ,Qpt, , , , , , 
"Latest Pleistocene alluvium, undifferentiated",Qpa,Qpa,Qpa,Qpaf, ,Qpaf,"Qmu, 
	Qml",Qpa,Qpa
Pleistocene marine terrace deposits,Qmt,Qmt,"Qpm, Qom",Qmt, , , ,Qpmt,Qmt
Early to late Pleistocene pediment deposits,Qop, , , , , , , , 
Early to late Pleistocene alluvial fan deposits,Qof, , ,"Qpaf, Qpoaf", , , , 
	,Qof
Early to late Pleistocene stream terrace deposits,Qot, , , , , , , , 
Early to late Pleistocene undifferentiated alluvial deposits*,Qoa,Qoa,Qoa,"Qpaf, 
	Qpoaf", , ,"Qru, Qrl","Qpea, Qpmc",Qoa
bedrock,br, , , , ,br, , , 


  * Includes Colma Formation.



Table 3.  Documentation of mapping procedures and sources of information.

1.	Original mapping conducted for this project by Keith L. Knudsen, Janet 
	M. Sowers, and Robert C. Witter.  The mapping is based on:

1a.	Interpretation of topographic contours, published soil surveys, 
	stereoscopic aerial photography dating from 1939 and 1949, historical 
	wetlands information compiled by the San Francisco Estuary Institute 
	(1998), Sowers (1999), other historical wetlands information, and 
	limited field reconnaissance.  Previous mapping reviewed includes Helley
	and Wesling (1989, 1990), Helley and Miller (1992), Helley and others 
	(1994), and Helley and Graymer (1997b).  Lead author: Sowers.  Map 
	scale: 1:24,000. 
	
1b.  	Interpretation of topographic contours, published soil surveys, and 
	stereoscopic aerial photography dating from 1939 to 1960, and limited 
	filed reconnaissance. Previous mapping reviewed includes Helley and 
	others (1979), Brabb and others (1998a and 1998b), and Angell and others 
	(1997).  Mapping of marine terraces is modified from Weber and others 
	(1993), and unpublished mapping by K.R. Lajoie.  Lead authors: Knudsen, 
	Sowers, and Witter.  Map scale: 1:24,000.

1c.  	Interpretation of topographic contours shown on modern and/or historical
	(circa 1915) U.S. Geological Survey maps, and published soil surveys. 
	Previous mapping reviewed includes Helley and others (1979), and Helley 
	and Harwood (1985), and unpublished maps of marine terraces by Ken 
	Lajoie. U.S. Geological Survey orthophotoquads dated 1970 were reviewed 
	for the Dozier, Elmira, and Allendale quadrangles.  Lead author: 
	Knudsen.  Map scale: 1:24,000.

1d.	Interpretation of topographic contours, published soil surveys, 
	stereoscopic aerial photography dating from 1939 to 1960, and limited 
	field reconnaissance.  Previous mapping reviewed includes Bonilla 
	(1998), Brabb and others (1998a) Lajoie and others (1974), Lajoie and 
	others (1979), Nichols and Wright (1971) and Pampeyan (1994).  Lead 
	author: Witter.  Map scale: 1:24,000


2.	Modified from Helley and Graymer (1997a, b).  Unit names and symbols 
	were modified to conform to stratigraphic nomenclature for this project.
	Map scale: 1:24,000.

2a.	Minor to moderate revisions were made to unit contacts or age 
	estimations of units to conform to more recent observations on this or 
	adjacent quadrangles. Atwater (1982) also was consulted for the 
	Brentwood quadrangle.  Lead authors: Knudsen and Sowers.

2b.	Extensive revisions were made based on interpretation of topographic 
	contours and soil surveys. Many unit contacts were redrawn and new units
	may have been delineated.  Age estimates of units may have been changed.
	In these quadrangles Helley and Graymer (1997b) is based on previous 
	mapping by Herd (1977).  Lead author: Sowers.

2c.	Extensive revisions were made based on interpretation of topographic 
	contours, 1949 stereoscopic aerial photography, and published soil 
	surveys. Many unit contacts were redrawn and new units may have been 
	delineated.  Age estimates of units may have been changed.  In this area
	Helley and Graymer (1997b) is based on previous mapping of Herd (1977). 
	Lead author: Sowers.

3.	Modified from Helley and others (1994).  Unit names and symbols were 
	modified to conform to stratigraphic nomenclature for this project.  
	Lead author: Sowers.  Map scale: 1:24,000.

3a.	Minor to moderate modifications were made to unit contacts or age 
	estimates of units.

3b.	Extensive modifications were made based on the interpretation of 
	orthophotoquads (dating from 1970 to the present), topographic contours, 
	and published soil surveys. Many unit contacts were redrawn and new 
	units may have been delineated.  Age estimates of units may have 
	changed.  

4.	Modified from Sawyer (1996).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature used in this project.  Minor 
	revisions were made to unit contacts based on interpretation of aerial 
	photography dating from 1939 and 1949, topographic contours, and 
	published soil surveys.  Lead author: Sowers.  Map scale: 1:24,000.

5.	Modified from Kelson and others (1993).  Unit names and symbols were 
	modified to conform to stratigraphic nomenclature used in this project.  
	Minor revisions were made to unit contacts based on interpretation of 
	aerial photography dating from 1939 and 1949, topographic contours, and 
	published soil surveys.  Lead author: Sowers.  Map scale: 1:24,000.

6.	Sowers and others (1998).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature used in this project.  Map scale: 
	1:100,000.

7.	Sowers and others (1997).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature for this project.  Map scale:
	1:24,000.

8.	Bezore, Sowers, and Randolph (2000).  Unit names and symbols were 
	modified to conform to stratigraphic nomenclature used in this project. 
	Map scale: 1:24,000.

9.	Modified from Atwater (1982).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature for this project. Mapping of 
	artificial levees and older alluvial fans was added based on 
	interpretation of modern and/or historical (circa 1915) topographic 
	maps.  Lead author: Knudsen.  Map scale: 1:24,000.

10.	Knudsen and others (1997).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature for this project.  Map 
	scale:1:100,000.

11.	Modified from Wentworth and others (1998).  Unit names and symbols were 
	modified to conform to stratigraphic nomenclature used in this project. 
	Lead authors: Sowers and Knudsen.  Map scale: 1:100,000.

11a.	Minor modifications were made based on the interpretation of topographic
	contours and published soil surveys.

11b.	Extensive modifications were made based on the interpretation of 
	topographic contours, 1970 orthophotoquads, and published soil surveys. 
	Many unit contacts were redrawn and new units may have been delineated. 
	Age estimates of units may have changed.  Helley and Nakata (1991) was 
	referred to for the Gilroy quadrangle. 

12.	Knudsen and Lettis (1997).  Additional published mapping for these 
	quadrangles includes Sowers and others (1993a and b), Noller and others 
	(1993), and Atwater (1982).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature used in this project.  Map scale: 
	1:24,000.

13.	Modified from Graymer (1997).  Unit names and symbols were modified to 
	conform to stratigraphic nomenclature used in this project.  Lead 
	author: Sowers.  Map scale: 1:24,000.

13a.	Minor modifications were made based on the interpretation of topographic 
	contours and published soil surveys.

13b.	Extensive modifications were made based on the interpretation of 
	topographic contours and published soil surveys.  Contacts between the 
	Holocene deposits were redrawn.  Age estimates of terraces along the 
	Pajaro River were revised.  



Figure 3.  Index map to Table 3.  Each rectangle represents a U.S. Geological 
Survey 7.5-minute quadrangle partly or wholly within the nine-county San 
Francisco Bay Region.  Mapping procedures and sources represented by codes (1a 
to 13b) are keyed to Table 2: Documentation of mapping procedures and data 
sources.  Colors indicate relative completion of Quaternary mapping.  At 
50-percent completion, existing mapping has been reinterpreted and modified to 
fit the stratigraphic nomenclature used herein, whereas 100 percent indicates 
original mapping involving: (1) review of existing maps, (2) interpretation of 
topography and landforms using maps and stereo-paired aerial photographs, (3) 
review of soil surveys published by the U.S. Natural Resources Conservation 
Service, and (4) field reconnaissance.  Counties and 1:100,000-scale U.S. 
Geological Survey quadrangles are also shown. 


The new mapping followed a standard procedure.  We assembled and reviewed 
available sources of information, including published soil surveys, historical 
topographic and early U.S. Coast Survey maps, aerial photography, previously 
published and unpublished geologic mapping, and personal field notes and 
observations.  From the 1:24,000-scale topographic map we traced water bodies, 
artificial levees, gravel quarries, and stream channels having a watershed area 
of about 5 square km or greater.  Our mapping of these features therefore 
reflects the current edition of the topographic map.  Where equivalent, the 
digital representations of these water boundaries were taken instead from 
standard U.S. Geological Survey Digital Line Graphs (DLGs).  Next, using 
pre-development (1939-1960) stereoscopic aerial photography and topographic 
contours on 7.5-minute quadrangles, we mapped bedrock/alluvial contacts, 
boundaries of stream terraces, extent of older alluvial fan remnants, and other 
fluvial features visible either in the topography or as tonal features apparent 
on aerial photographs. 

Published soil surveys served as one of the primary sources of information on 
ages of deposits.  Individual soil series in the region typically are associated
with Quaternary units of specific age and environment of deposition (Appendix 
B), although their mapped boundaries may not match well with our unit boundaries
because of differences in mapping techniques.  Soil surveys for the study area 
include Bates (1977), Cosby (1941), Gardner and others (1958), Kashiwagi (1985),
Lambert and Kashiwagi (1978), Lindsey and Weisel (1974), Miller (1972), Welch 
(1977, 1981), and Welch and others (1966).

Historical maps and compilations of San Francisco Bay shoreline and tidal 
marshes were used to delineate the margins of the Holocene Bay Mud (Qhbm) and 
the extent of Bay Mud now buried beneath artificial fill (afbm).  Mapping of the
extent of artificial fill and artificial levees by R.W. Graymer (Helley and 
Graymer, 1997a, 1997b) also was used.  The U.S. Coast Survey mapped the entire 
San Francisco Bay shoreline and tidal marshes between 1850 and 1900 .  These 
maps were compiled on modern base maps by Nichols and Wright (1971).  For most 
areas, the tidal marsh limit as shown on the Nichols and Wright (1971) 
compilation was used as a proxy to delineate the extent of Bay mud.  The San 
Francisco Estuary Institute Goals Project (1998) produced a later map that 
incorporates additional historical information and includes revised registration
of the U.S. Coast Survey maps, but this map and its documentation were not 
available for all areas.  These maps, and creek and watershed maps by Sowers 
(1995, 1997, 1999), which use data from the San Francisco Estuary Institute 
(1998), the U.S. Coast Survey maps, and early aerial photography, also were 
consulted when mapping late Holocene features and deposits.   

The resulting manuscript maps were digitized at the U.S. Geological Survey under
the direction of Carl Wentworth.  Each map was scanned, vectorized, edited and 
attributed.  A proof plot was reviewed and revised by the lead authors.  
Boundary problems between adjacent quadrangles were identified and corrected, 
where possible.  Some boundary problems remain but will be resolved in the 
future as we finish inserting new, 1:24,000-scale original mapping into the 
database.

Table 3 describes: (1) the procedure used in developing the Quaternary geologic 
maps, (2) the sources of information and references used, and (3) the relative 
level of detail or map scale.  The numbers in the table are keyed to the 
accompanying index map (figure 3).  This information is intended both to 
document and credit our sources and to assist the reader in judging the relative
quality of the mapping.  For example, mapping that includes the interpretation 
of stereoscopic aerial photography can be expected to be more accurate and 
precise than that based solely on the interpretation of topographic contours and
soil surveys. 

Previous studies document a correlation between the age and environment of 
deposition and the tendency of a deposit to liquefy (Tinsley and others, 1985; 
Tinsley and Holzer, 1990).  Age is important because sediment becomes more 
consolidated, weathered, and cemented with time.  Depositional environment is 
important because different environments produce deposits with different 
sorting, bedding, and grain-size characteristics.  Stream channel deposits, for 
example, are likely to contain sand and silt, and where young (late Holocene), 
they are likely to be loose and nearly cohesionless.  

Liquefaction susceptibility units were designated on the basis of a criteria 
matrix that assigns susceptibility values to all combinations of geologic unit 
(type and age of the deposit) and ground-water level (table 4).  The resulting 
units reflect the likelihood that loose, saturated, granular sediment is present
within 50 feet of the ground surface.  The matrix was calibrated using 
information on past occurrences of liquefaction, previous geologic and 
geotechnical studies by WLA., and limited boring log data that includes standard
penetration test (SPT) information.  Where appropriate SPT data were available, 
they were analyzed to evaluate the typical peak ground acceleration (PGA) needed
to cause liquefaction using the Seed Simplified procedure (Seed and Idriss, 
1971, 1982; Youd and Idriss,1997).  Because extensive borehole analysis was 
beyond the scope of this study, we have relied on these limited analyses, WLA's 
experience on other projects in the area, and an unpublished database developed 
by CDMG in its seismic hazard zonation mapping of the cities of Oakland and San 
Francisco.  

Data on the depth to ground water were developed in several ways.  Information 
on ground-water depths from boring logs for geotechnical studies was obtained 
from the California Department of Transportation, the Bay Area Rapid Transit 
District, and from reports on file with several county and city governments in 
the region.  Data also were collected in the field by measuring the depth to the
water surface in streams, creeks, and drainage ditches with respect to the 
adjacent terrace or fan surface into which the stream is incised.  We also used 
the depth of stream incision as a proxy default maximum depth to ground water.  
In making these measurements, we assumed that the stream bed was representative 
of the level of shallow ground water in the area.  From those observations or 
boring log data we extrapolated water levels to areas with little available 
ground-water data.  Levels in water wells were not used because these represent 
the potentiometric surface of the ground-water aquifer in which the well is 
completed, not the depth to shallow saturated sediment.  Where historical high 
ground-water levels are known, we use those levels to ensure conservatism in our
liquefaction susceptibility assignments.  This use of historical high 
ground-water levels is consistent with CDMG's use of historical high 
ground-water levels in its Seismic Hazard Mapping Program.


Table 4.  Criteria matrix for assigning liquefaction susceptibility units.  
Units indicate relative susceptibility of deposits to liquefaction as a function
of groundwater depth within that deposit.  VH = very high, H = high, M = 
moderate, L = low, and VL = very low to none.  The shaded boxes show the 
selected susceptibility assignment(s) for each geologic unit.

  [Lines of the table are presented here as comma-delimited records]

Geologic unit,Description,Historical occurrence of liquefaction in 
	unit?,Estimated acceleration to trigger liquefaction in sandy and silty 
	material (-1),Typical depth to ground water (ft),Depth to groundwater 
	(ft) and liquefaction susceptibility category assigned to geologic unit 
	<10,10 to 30,30 to 50,>50

af,Artificial fill (2),yes,0.1g (3),<10,L (2),L (2),L to VL,VL
afbm,Artificial fill over Bay Mud,yes,0.1g (3),<10,VH,H,M,VL
alf,"Artificial fill, levee",yes,0.1g (3),<15,VH ,H,M,VL
ads,Dredge spoils,no,0.1g (3),<10,VH,VH,M,VL
gq,Gravel quarry,no,uncertain,variable,H,M,L,VL
ac,Artificial stream channel,no,uncertain,<5,L,L,L,L
Qhc,Modern stream channel deposits,yes,0.1g,<5,VH,H,M,VL
Qhfy,Latest Holocene alluvial fan deposits,yes,0.2g,<20,VH,H,M,L
Qhly,Latest Holocene alluvial fan levee deposits,yes,0.2g,<20,VH,H,M,L
Qhty,Latest Holocene stream terrace deposits,uncertain (4),0.2g,<10,VH,H,M,L
Qhay,"Latest Holocene alluvial deposits, undifferentiated",yes,0.2g,<10,VH,H,M,L
Qhfp,"Late Holocene alluvial floodplain deposits, 
	undifferentiated",no,0.2g,<10,VH,H,M,L
Qhfb,Late Holocene flood basin deposits,no,0.2g,<10,H,H,M,L
Qhbs,Holocene beach sand,yes,0.1g,<10,VH,H,M,VL
Qhds,Holocene dune sand,uncertain(4),0.2g,<20,VH,H,M,VL
Qhbm,Holocene San Francisco Bay mud,yes,0.2g,<5,H,H,M,VL
Qhdm,Holocene San Joaquin/ Sacramento Delta mud and 
	peat,uncertain(4),0.2g,<5,H,H,M,VL
Qhb,Holocene basin deposits,uncertain(4),0.2 to 0.4g,<10,H,M,L,VL
Qhfe,Holocene fine grained alluvial fan-estuarine complex deposits,yes,0.2 to 
	0.4g,<10,H,M,L,VL
Qhf,Holocene alluvial fan deposits,yes,0.3 to 0.5g,<15,M,M,L,VL
Qhff,"Holocene alluvial fan deposits, fine facies",yes,0.3 to 0.5g,<10,H,M,L,VL
Qhl,Holocene alluvial fan levee deposits,yes,0.3 to 0.5g,<15,M,M,L,VL
Qht,Holocene stream terrace deposits,yes,0.2 to 0.3g,<10,H,H,M,VL
Qha,"Holocene alluvium, undifferentiated",yes,0.2 to 0.5g,<10,H,H,M,VL
Qds,Latest Pleistocene to Holocene dune sand,yes,>0.3g,<25,M,M,L,VL
Qb,Latest Pleistocene to Holocene basin deposits,no,>0.3g,<15,M,L,L,VL
Qf,Latest Pleistocene to Holocene alluvial fan deposits,yes,>0.3g,<25,M,L,L,VL
Ql,Latest Pleistocene to Holocene alluvial fan levee 
	deposits,no,>0.3g,<25,M,L,L,VL
Qt,Latest Pleistocene to Holocene stream terrace deposits,no,>0.3g,<15,M,M,L,VL
Qa,"Latest Pleistocene to Holocene alluvium, 
	undifferentiated",yes,>0.3g,<15,M,M,L,VL
Qpb,Latest Pleistocene basin deposits,no,uncertain,<20,L,L,VL,VL
Qpf,Latest Pleistocene alluvial fan deposits,yes,>0.5g,<30,L,L,VL,VL
Qpt,Latest Pleistocene stream terrace deposits,no,>0.5g,<30,L,L,VL,VL
Qpa,"Latest Pleistocene alluvium, undifferentiated",no,>0.5g,<30,L,L,VL,VL
Qmt,Pleistocene marine terrace deposits,uncertain(4),uncertain,<30,L,L,VL,VL
Qop,Early to late Pleistocene pediment deposits,no,uncertain,<40,L,VL,VL,VL
Qof,Early to late Pleistocene alluvial fan deposits,no,>0.6g,<40,L,VL,VL,VL
Qot,Early to late Pleistocene stream terrace deposits,no,>0.6g,<40,L,VL,VL,VL
Qoa,"Early to late Pleistocene alluvium, undifferentiated",uncertain 
	(4),>0.6g,<40,L,VL,VL,VL
br,Bedrock,no,NA,variable,VL,VL,VL,VL


Notes:
(1) Based on the Simplified Seed approach (Seed and Idriss, 1982, Youd and 
Idriss, 1997) and a limited number of borehole analyses for some units. 
(2) The liquefaction susceptibility of artificial fill ranges widely, depending 
largely on the nature of the fill and whether it was compacted.  We use very 
high susceptibility for all fill on the margins of the San Francisco Bay (afbm), 
and somewhat arbitrarily assign a low susceptibility to all upland fills (af).  
Liquefaction susceptibility assignments for fewer than ten artificial fill (af) 
polygons are shown as VH of H, based on the occurrence of liquefaction in these 
areas.   
(3) Assuming non-engineered fill.
(4) These occurrences are either not well located, or are poorly 
characterized in historical accounts and may not have been liquefaction related. 

                                  RESULTS

Quaternary deposits in the region occur in many settings, including: (1) 
northwest-trending, structurally controlled valleys; (2) alluvial piedmonts 
sloping away from the flanks of northwest-trending mountainous ranges; (3) areas
of primarily latest Pleistocene sand dunes on the northern San Francisco 
Peninsula, in the Oakland area, and near the Sacramento/San Joaquin Delta; (4) 
deltaic, beach and marine terrace environments along the Pacific coast; and (5) 
estuarine environments around the margins of San Francisco Bay and the 
Sacramento/San Joaquin Delta.  Large northwest-trending valleys, such as those 
adjacent to Walnut Creek, Coyote Creek, Guadalupe Creek, Russian River, and Napa
River, contain sediment deposited by streams on flood plains, alluvial fans, and
basins.  Sedimentary deposits in smaller intermontane valleys are similar to 
those of the larger valleys, but are thinner and smaller in areal extent.  Along
the west side of the East Bay hills, coalescing alluvial fans have formed a 
broad alluvial piedmont that extends from Richmond southeast past Oakland and 
Fremont.  Eolian deposits mantle the northern San Francisco Peninsula and 
interfinger with bay margin sediment along the shoreline near Oakland and 
Antioch (Atwater and others, 1977; Rogers and Figuers, 1991).  Coastal and 
estuarine areas contain deltaic sediment, beach and dune sand, and marine 
terrace deposits.  

Appendix A presents descriptions of the Quaternary stratigraphic units mapped in
the region. Figure 2 shows the stratigraphic relations among the units, and 
table 2 compares the stratigraphic units with those of previous researchers in 
the area.  We characterize engineering geologic properties of some of the units 
in a preliminary way using subsurface information gathered by WLA in consulting 
investigations and by the CDMG Seismic Hazards Mapping Program in the areas of 
Oakland (Haydon and others, 1999), San Francisco (DeLisle and Real, 1994) and 
the San Jose East quadrangle (Clahan and others, 2000). 

Man-made deposits cover approximately 2 percent of the region.  These areas are 
mapped as either artificial fill (af), artificial fill over Bay Mud (afbm), 
artificial levee fill (alf), dredge spoils (ads), or gravel quarry and 
percolation pond (gq).  Artificial fill over Bay Mud (afbm) is mapped where fill
was placed over Bay Mud, bayward of the early historical extent of marshlands 
and bay (Nichols and Wright, 1971; Goals Project, 1999).  Artificial levee fill 
(alf) was mapped where the map symbols for levees are shown on 7.5-minute U.S. 
Geological Survey topographic quadrangles.  Artificial levee deposits (alf) may 
not differ significantly from the underlying material where this material is 
artificial fill over Bay Mud (afbm) or artificial fill (af).  Atwater's (1982) 
mapping of dredge spoils (ads) was adopted in the San Joaquin/Sacramento Delta 
area.  Dredge spoils (ads) may be very similar in nature to artificial fill over
Bay Mud (afbm).  The unit gravel quarry and percolation pond (gq) typically was 
mapped using information shown on 7.5-minute U.S. Geological Survey topographic 
or orthophoto quadrangles.

The region included within the nine counties bordering the San Francisco Bay is 
approximately 18,000 square kilometers in area.  We map about 70 percent of this
area as bedrock, about 19 percent as Holocene deposits, and about 9 percent as 
latest Pleistocene or latest Pleistocene to Holocene undifferentiated.  Almost 6
percent of the area is mapped as Holocene alluvial fan deposits, the most 
areally extensive Quaternary unit.  The units latest Pleistocene alluvial fan 
deposits, Holocene Bay Mud, and Holocene alluvial fan deposits fine grained 
facies, each account for between 3 and 4 percent of the total area.  


                                  Ground water

Liquefaction of sediment requires that the sediment be water saturated.  For 
this regional characterization, we have estimated a typical depth to ground 
water for each Quaternary map unit (table 4).  In more detailed work, in 
contrast, depth to water would be treated as a continuous and independent 
variable.  The depth to ground water in areas underlain by Holocene alluvial, 
estuarine, and beach sediment is generally less than 10 feet throughout most of 
the study area.  In general, ground water is deeper beneath topographically 
higher parts of the landscape (for example, uplifted and dissected Pleistocene 
alluvial fans), and closer to the surface of topographically lower parts of the 
landscape (for example, Holocene basins and terraces).  Pronounced seasonal 
changes in ground-water levels occur in the region, with variations as large as 
tens of feet.  Thus, in order to use historical high ground-water levels 
consistently, we have sought information on ground-water levels measured during 
and soon after the rainy season of wetter years.  

Small, isolated alluviated valleys and pockets within the bedrock hills appear 
to have fairly shallow ground water, generally less than 10 to 15 feet.  Soils 
characteristic of wet environments are mapped in many of these valleys, and the 
few data available on depth to ground water indicate shallow ground-water 
levels.  Depths to ground water beneath marine terraces and dune sand can be 
significantly greater than beneath other Quaternary deposits in the region.  
Ground water beneath uplifted marine terraces can be deeper than 40 feet, except
where water is perched.  Ground water beneath coastal dunes that form or mantle 
hills can be as deep as 50 to 100 feet, equivalent to the elevation of the 
hills.


                  Historical liquefaction in the nine-county 
                          San Francisco Bay Region

Records of liquefaction-induced ground failures in the region are available for 
several historic earthquakes; including the two most damaging events: the 1906 
San Francisco earthquake (M=8.3) (Youd and Hoose, 1978), and the 1989 Loma 
Prieta earthquake (M=7.1) (Plafker and Galloway, 1989; Seed and others, 1990; 
Tinsley and others, 1998).  Other earthquakes that generated liquefaction 
failures in the study area include the 1838, 1865, 1868, and 1957 earthquakes 
(Youd and Hoose, 1978). Much of the 1989 liquefaction-related ground failures 
occurred in areas of previous (for example 1906) liquefaction (Dupr and 
Tinsley, 1990; Seed and others, 1990).  

We have developed a preliminary spatial database of earthquake-induced ground 
effects in the San Francisco Bay Region (Appendix C) and compared the locations 
of past ground effects with the new digital Quaternary deposits map.  The 
ground-failure database contains historical observations interpreted from Youd 
and Hoose (1978), and observations of liquefaction-related ground effects 
resulting from the 1989 Loma Prieta earthquake, (Tinsley and others, 1998).  The
ground effects database (Appendix C) is preliminary and will receive additional 
review and revision in the near future.  Table 5 shows the results of our 
preliminary analysis relating the location of liquefaction-related ground 
effects in the San Francisco Bay Region to the Quaternary map units. 


Table 5.  Preliminary evaluation of relations between mapped occurrences of 
liquefaction and Quaternary geologic map units and liquefaction susceptibility 
assignments in the nine-county San Francisco Bay region.  

  [Lines of the table are presented here as comma-delimited records]

Map unit symbol,# of occurrencespre-Loma Prieta,# of occurrencesLoma 
Prieta,Percent of total,Regional liquefaction susceptibility assignments (1)
af,11,,3,L
afbm,88,112,47,VH
alf,1,4,1,H
ads,0,0,0,VH
gq,0,0,0,H
ac,0,0,0,L
Qhc,14,0,3,VH
Qhfy,7,0,2,VH
Qhly,3,1,1,VH
Qhty,0,0,0,VH
Qhay,8,0,2,VH
Qhbs,1,3,1,VH
Qhfp,0,0,0,VH
Qhfb,0,0,0,H
Qhds,0,0,0,VH
Qhbm,17,1,4,H
Qhdm,0,0,0,H
Qhb,0,0,0,H
Qhfe,0,1,0,H
Qhf,12,0,3,M
Qhff,10,0,2,H
Qhl,8,0,2,M
Qht,3,0,1,H
Qha,22,0,5,H
Qds,16,0,4,M
Qb,0,0,0,L
Qf,1,0,0,L
Ql,0,0,0,L
Qt,0,0,0,M
Qa,12,0,3,M
Qpb,0,0,0,L
Qpf,2,0,0,L
Qpt,0,0,0,L
Qpa,0,0,0,L
Qmt,1,0,0,L
Qof,0,0,0,VL
Qop,0,0,0,VL
Qot,0,0,0,VL
Qoa,9,0,2,VL
br (2),31,0,7,VL
water,14,13,6,---

totals,291,135,100,---

Notes:
(1) See next section for discussion of liquefaction susceptibility categories; 
VH-very high; H-high; M-moderate; L-low; VL-very low.
(2) The occurrence of many liquefaction-induced ground failures in the map units
bedrock and water is a reflection of the preliminary nature of the liquefaction 
occurrence database.

A prominent conclusion is that the map unit "afbm" (artificial fill over Bay 
Mud) has hosted about 50 percent of all historical liquefaction occurrences in 
the San Francisco Bay Region and about 80 percent of the liquefaction 
occurrences resulting from the Loma Prieta earthquake.  For the Loma Prieta 
earthquake, the higher percentage may reflect that only low accelerations are 
needed to trigger liquefaction in this unit, and that most of the region 
experienced only relatively low accelerations from the Loma Prieta earthquake.  
In many of theses cases, however, it is not known whether the liquefaction was 
in the fill or in the underlying Bay Mud deposits.  The high percentage of 
failures occurring in artificial fill over Bay Mud also may reflect 
amplification of the shaking by the soft Bay Mud.  


                   Liquefaction susceptibility units

Tinsley and others (1985) defined liquefaction susceptibility units based on 
quantitative evaluation of SPT values from boreholes in the Los Angeles area.  
In their analyses, they assumed a relatively constant shaking hazard across the 
study area and also assumed that potential shaking levels everywhere within the 
Los Angeles region are sufficient to trigger liquefaction of susceptible 
materials.  Deposits rated Very High and High by Tinsley and others (1985) are 
expected to capture most of the liquefaction that occurs in an earthquake of 
magnitude 6.5 or greater.  Parts of deposits rated Moderate are expected to 
liquefy in a magnitude 8 event but not a magnitude 6.5 event, and deposits rated
Low or Very Low are unlikely to liquefy, even in a magnitude 8 earthquake.  Our 
liquefaction susceptibility methodology and categories parallel those of Tinsley
and others (1985).  

The liquefaction susceptibility units defined in this report are based on peak 
ground accelerations (PGA) necessary to trigger liquefaction and estimated 
ground-water levels for each map unit (table 4).  The PGA values required to 
trigger acceleration that are presented in table 4 are estimates only, and are 
provided only to indicate relative levels of shaking necessary to liquefy 
different geologic units.  Typical PGAs necessary to induce liquefaction of 
sandy or silty materials range from as low as 0.1 g for saturated artificial 
fill and modern stream channel deposits, to much greater than 0.5 to 0.6 g for 
saturated latest Pleistocene alluvial deposits.  

On the basis of the liquefaction failures that occurred during past earthquakes,
we expect that at least 80 percent of future liquefaction failures will take 
place in areas judged to have High or Very High susceptibilities.  We expect 
that 20 percent or less of future liquefaction will take place in areas judged 
to be Moderate and Low, and that less than 1 percent will take place in areas 
judged Very Low.  Geologic units known to have liquefied in previous earthquakes
generally are assigned to the Very High category, although where either the 
location of the event or the actual occurrence of liquefaction is in question, 
we may have assigned the geologic unit to the "High" or "Moderate" 
susceptibility units, depending on the geologic unit.


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  surrounding parts of Alameda, Marin, Sonoma, Solano, Sacramento, and San 
  Joaquin Counties, California: a digital database: U.S. Geological Survey 
  Open-File Report 97-98.

Helley, E.J., and Graymer, R.W., 1997b, Quaternary geology of Alameda County and
  parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and 
  San Joaquin Counties, California: a digital database: U.S. Geological Survey 
  Open-File Report 97-97.

Helley, E.J., and Harwood, D.S., 1985, Geologic map of the Late Cenozoic 
  deposits of the Sacramento Valley and northern Sierran Foothills, California: 
  U.S. Geological Survey Miscellaneous Field Studies Map MF-1790, scale 
  1:62,500.

Helley, E.J., and Miller, D.M., 1992, Geologic map of the Newark 7.5 minute 
  quadrangle, Alameda County, California: U.S. Geological Survey Open-File 
  Report 92-312, scale 1:24,000.

Helley, E.J., and Nakata, J., 1991, Geologic map of the Gilroy 7.5-minute 
  quadrangle: U.S. Geological Survey Open-File Report 91-278.
Helley, E.J., and Wesling, J., 1989, Quaternary geologic map of the Milpitas 
  quadrangle, California, 1:24,000: U.S. Geological Survey Open-File Report 
  89-671.

Helley, E.J., and Wesling, J.R., 1990, Quaternary geologic map of the San Jose 
  East quadrangle, Santa Clara County, California:  U.S. Geological Survey 
  Open-File Report 90-427.

Helley, E.J., Graymer, R.W., Phelps, G.A., Showalter, P.K., and Wentworth, C.M.,
  1994, Preliminary Quaternary geologic maps of Santa Clara Valley, Santa Clara,
  Alameda, and San Mateo Counties, California, a digital database: U.S. 
  Geological Survey Open-File Report 94-231.

Helley, E.J., Lajoie, K.R., Spangle, W.E., and Blair, M.L., 1979, Flatland 
  deposits of the San Francisco Bay Region, California - Their geology and 
  engineering properties, and their importance to comprehensive planning:  U.S. 
  Geological Survey Professional Paper 943, 88 p.

Herd, D.G., 1977, Geologic map of the Las Positas, Greenville, and Verona 
  faults, eastern Alameda County, California: U.S. Geological Survey Open-file 
  Report 77-689, 1:24,000.

Holzer, T.L., Tinsley, J.C., III, Bennett, M.J., and Mueller, C.J., 1994, 
  Observed and predicted ground deformation - Miller Farm lateral spread, 
  Watsonville, California:  Buffalo, New York, National Center for Earthquake 
  Engineering Research Technical Report NCEER-94-0026, p. 79-99.

Jack, R.N., 1969, Quaternary sediments of the Montara Mountain area, San Mateo 
  County, California: unpublished Masters Thesis, University of California, 
  Berkeley.

Kashiwagi, J., 1985, Soil Survey of Marin County, California: U.S. Department of
  Agriculture, Soil Conservation Service, 229 p., 13 map sheets at 1:24,000 
  scale.

Kashiwagi, J.H. and Hokholt, L.A., 1991,  Soil survey San Mateo County, eastern 
  part, and San Francisco County, California: U.S. Department of Agriculture, 
  Soil Conservation Service, 120 p., 12 map sheets at 1:24,000 scale.

Keefer, D.K., ed., 1998, The Loma Prieta, California, earthquake of October 17, 
  1989-landslides: U.S. Geological Survey Professional Paper 1551-C.

Kelson, K.I., Simpson, G.D., Haraden, C.C., Sawyer, T.L., and Hemphill-Haley, 
  M.A., 1993, Late Quaternary surficial deformation of the southern East Bay 
  Hills: Final Technical Report, National Earthquake Hazards Reduction Program, 
  U.S. Geological Survey, Award #1434-92-2209.

Knudsen, K.L., and Lettis, W.R., 1997, Preliminary maps showing Quaternary 
  geology of twenty 7.5-minute quadrangles, eastern Stockton, California, 
  1:100,000 quadrangle: National Earthquake Hazards Reduction Program, U.S. 
  Geological Survey, Final Technical Report, Award #1434-94-G-2499.

Knudsen, K.L., Noller, J.S., Sowers, J.M., Lettis, W.R., Graham, S.E., Randolph,
  C.E., and May, T.E., 1997, Quaternary geology and liquefaction susceptibility,
  San Francisco, California 1:100,000 quadrangle: a digital database: U.S. 
  Geological Survey Open-File Report 97-715, scale 1:100,000.

Lajoie, K.R., Helley, E.J., Nichols, D.R., and Burke, D.B., 1974, Geologic map 
  of unconsolidated and moderately consolidated deposits of San Mateo County: 
  U.S. Geological Survey Miscellaneous Field Studies Map MF-575, scale 1:62,500.

Lajoie, K.R., Weber, G.E., Mathieson, S., and Wallace, J., 1979, Quaternary 
  tectonics of coastal Santa Cruz and San Mateo Counties, California, as 
  indicated by deformed marine terraces and alluvial deposits, in Weber, G.E., 
  Lajoie, K.R., and Griggs, G.B. eds., Coastal tectonics and coastal geologic 
  hazards in Santa Cruz and San Mateo Counties, California: Field Trip Guide, 
  Cordilleran Section of the Geological Society of America, 75th Annual Meeting,
  p. 61-80.

Lambert, G., and Kashiwagi, J., 1978, Soil Survey of Napa County, California: 
  U.S. Department of Agriculture, Soil Conservation Service, 104 p., 47 map 
  sheets at 1:24,000 scale.

Lettis, W.R., 1982, Late Cenozoic stratigraphy and structure of the western 
  margin of the central San Joaquin Valley, California:  U.S. Geological Survey 
  Open-File Report 82-526, 203 p.

Lettis, W.R., 1985, Late Cenozoic stratigraphy and structure of the West-Central
  San Joaquin Valley, California:  in Weide, D., ed., Quaternary Soils and 
  Geomorphology of the American Southwest, Geological Society of America, 
  Special Paper 203, p. 97-114. 

Lindsey, W.D., and Weisel, C.J., 1974, Soil survey of the eastern Santa Clara 
  area, California:  U.S. Department of Agriculture, Soil Conservation Service, 
  90 p., 49 map sheets at 1:24,000 scale.

Marchand, D.E., and Allwardt, A., 1978, Quaternary deposits, northeastern San 
  Joaquin Valley, California:  U.S. Geological Survey Miscellaneous Field 
  Studies Map MF-945, scale 1:125,000.

Marchand, D.E., and Allwardt, A., 1981, Late Cenozoic stratigraphic units, 
  northeastern San Joaquin Valley, California:  U.S. Geological Survey Bulletin 
  1470, 70 p.

Marchand, D.E., and Harden, J.W., 1978, Preliminary geologic maps showing 
  Quaternary deposits on the lower Tuolumne and Stanislaus alluvial fans and 
  along the lower San Joaquin River, Stanislaus County, California: U.S. 
  Geological Survey Open-File Report 78-656, 9 p., 4 sheets, scale 1:24,000. 

Matti, J.C., and Carson, S.E., 1991, Liquefaction susceptibility in the San 
  Bernardino Valley and vicinity, Southern California - A regional evaluation: 
  U.S. Geological Survey Bulletin 1898, 53 p. plus plates.

Mejia, L.H., Hughes, D.K., and Sun, J.I., 1992, Liquefaction at Moss Landing 
  during the 1989 Loma Prieta Earthquake:  Proceedings of the Tenth World 
  Conference, Earthquake Engineering, p. 1435-1440.

Miller, V.C., 1972, Soil survey of Sonoma County, California: U.S. Department of
  Agriculture, Soil Conservation Service, 188 p., 123 map sheets at 1:20,000 
  scale. 

Nichols, D.R., and Wright, N.A., 1971, Preliminary map of historical margins of 
  marshland, San Francisco Bay, California: U.S. Geological Survey Open-File 
  Report, Basic Data Contribution 9, scale 1:125,000. 

Noller, J.S., Sowers, J.M., and Lettis, W.R., 1993, Preliminary Quaternary 
  geology of the Solyo and Lone Tree Creek 7.5-minute quadrangles, California:  
  U.S. Geological Survey Open-File Report 93-224.

Pampeyan, E.H., 1993, Geologic map of the Palo Alto and part of the Redwood 
  Point 7-1/2' quadrangles, San Mateo and Santa Clara Counties, California: U.S.
  Geological Survey Miscellaneous Investigation Series I-2371, scale 1:24,000.

Pampeyan, E.H., 1994, Geologic map of the Montara Mountain and San Mateo 7-1/2' 
  quadrangles, San Mateo County, California: U.S. Geological Survey 
  Miscellaneous Investigation Series I-2390, scale 1:24,000.

Perkins, J.B., Mikulis, K., and Kirking, B., 1999, Preventing the nightmare, 
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  earthquake retrofits:  Association of Bay Area Governments Publication Number 
  P99002EQK, Oakland, California.

Plafker, G., and Galloway, J.P., eds., 1989, Lessons learned from the Loma 
  Prieta, California, earthquake of October 17, 1989: U.S. Geological Survey 
  Circular 1045, 48 p.

Retzer, J.L., Glassey, T.W., Goff, A.M., and Harradine, F.F., 1951, Soil Survey 
  of the Stockton area: U.S. Department of Agriculture, Bureau of Plant 
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Rogers, J.D., and Figuers, S.H., 1991, Engineering geologic site 
  characterization of the greater Oakland-Alameda area, Alameda and San 
  Francisco Counties, California: Final Report to the National Science 
  Foundation, Grant no. BCS - 9003785.

San Francisco Estuary Institute, 1998, Bay Area EcoAtlas, ver 1.50b4, San 
  Francisco Estuary Institute, Richmond, California.

Sarna, A., 1967, Aerial extent and thickness of the bay mud in northern Santa 
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Sawyer, T.L., 1996, Unpublished surficial mapping conducted in support of the 
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  seismogenic sources, Livermore Valley, eastern San Francisco Bay region: Final
  Technical Report, National Earthquake Hazards Reduction Program, U.S. 
  Geological Survey, Award #1434-95-G-2611.

Schlocker, J., 1974, Geology of the San Francisco North quadrangle; U.S. 
  Geological Survey Professional Paper 782, 109 p., plates scale 1:24,000.

Seed, H.B., and Idriss, I.M., 1971, Simplified procedure for evaluating soil 
  liquefaction potential: Journal of the Soil Mechanics and Foundations Division
  of ASCE, v. 97: SM9, p. 1,249-1,273. 

Seed, H.B., and Idriss, I.M., 1982, Ground motions and soil liquefaction during 
  earthquakes:  Earthquake Engineering Research Institute, Engineering Monograph
  v. 5, 134 p. 

Seed, R.B., Dickenson, S.E., Riemer, M.F., Bray, J.D., Sitar, N., Mitchell, 
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  M.S., 1990, Preliminary report on the principal geotechnical aspects of the 
  October 17, 1989 Loma Prieta earthquake, Earthquake Engineering Research 
  Center, Report No. UCB/EERC-90/05. 

Sowers, J.M., 1999, Creek and watershed map of Fremont and vicinity: Oakland 
  Museum of California, Oakland, California, scale 1:26,000

Sowers, J.M., 1997, Creek & watershed map of Hayward and San Leandro: Oakland 
  Museum of California, Oakland, California, scale approx. 1:26,000.

Sowers, J.M., 1995, Creek & watershed map of Oakland and Berkeley: Oakland 
  Museum of California, Oakland, California, scale approx. 1:26,000.

Sowers, J.M., Noller, J.S., and Lettis, W.R. 1993a, Preliminary Quaternary 
  geology of the Tracy and Midway 7.5-minute quadrangles, California:  U.S. 
  Geological Survey Open-File Report 93-225.

Sowers, J.M., Noller, J.S., and Lettis, W.R. 1993b, Preliminary Quaternary 
  geology of the Patterson and Crows Landing 7.5-minute quadrangles, California:
  U.S. Geological Survey Open-File Report 93-223.

Sowers, J.M., Noller, J.S., and Lettis, W.R., 1995, Maps showing geology and 
  liquefaction susceptibility of the Napa 1:100,000 sheet: U.S. Geological 
  Survey Open-File Report 95-205.

Sowers, J.M., Noller, J.S., and Lettis, W.R., 1997, Quaternary geology and 
  liquefaction susceptibility maps of Napa County, 1:24,000: unpublished report 
  prepared for Napa County.

Sowers, J.M., Noller, J.S., and Lettis, W.R., 1998, Quaternary geology and 
  liquefaction susceptibility, Napa, California 1:100,000 quadrangle: a digital 
  database: U.S. Geological Survey Open-File Report 98-460.

Thomasson, H.G., Olmsted, F.H., and LeRoux, E.F., 1960, Geology, Water 
  Resources, and usable groundwater storage capacity of part of Solano County, 
  California:  U.S. Geological Survey Water-Supply Paper 1464, p. 48.

Tinsley, J.C., and Holzer, T.L., 1990, Liquefaction in the Monterey Bay Region, 
  in National Hazards Reductions Program, Summaries of Technical Reports, Vol. 
  XXX, U.S. Geological Survey Open-File Report 90-334, p. 642-643.

Tinsley, J.C., Dupre, W.R., and Bennett, M.J., 1999, Evaluating liquefaction 
  susceptibility maps and liquefaction-related ground failure: The Loma Prieta 
  experience:  EOS Transactions, v. 80, p. F40-F41.

Tinsley, J.C., III, Egan, J.A., Kayen, R.E., Bennett, M.J., Kropp, A., and 
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  associated effects: in Holzer, T.L., ed., The Loma Prieta, California, 
  Earthquake of October 17, 1989 - Liquefaction: U.S. Geological Survey 
  Professional Paper 1551-B.

Tinsley, J.C., Youd, T.L., Perkins, D.M., and Chen, A.T.F, 1985, Evaluating 
  Liquefaction Potential, in Ziony, J.I., ed., Evaluating earthquake hazards in 
  the Los Angeles Region - an earth-science perspective:  U.S. Geological Survey
  Professional Paper 1360, p. 263-316.

U.S. Department of Agriculture, Soil Survey Staff, 1994, Keys to Soil Taxonomy: 
  Pocahontas Press, Inc., Blacksburg, VA, 524 p.

Wagner, R.J. and Nelson, R.E., 1961, Soil Survey of San Mateo Area, California: 
  U.S. Department of Agriculture, Soil Conservation Service, Series 1954, no. 
  13, 112 p., 49 map sheets at 1:15,840 scale. 

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  Pleistocene and Holocene slip rates along the San Gregorio fault zone, San 
  Mateo County, California: Final Technical Report, National Earthquake Hazards 
  Reduction Program, U.S. Geological Survey, Award # 1434-93-G-2336.

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  of Agriculture, Soil Conservation Service, National Cooperative Soil Survey, 
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Welch, L.E., 1981, Soil survey Alameda County, California, western part: U.S. 
  Department of Agriculture, Soil Conservation Service, 103 p., 8 map sheets at 
  1:24,000 scale.

Welch, L.E., Huff, R.C., Dierking, R.A., Cook, T.D., Bates, L.A., Andrews, W.F.,
  1966, Soil survey Alameda area, California: U.S. Department of Agriculture, 
  Soil Conservation Service, Series 1961, No. 41, 95 p., 42 map sheets at 
  1:20,000 scale.

Wentworth, C.M., Blake, M.C., McLaughlin, R. J., and Graymer, R.W., 1998, 
  Preliminary geologic map of the San Jose 30 x 60 minute quadrangle, 
  California: a digital database: U.S. Geological Survey Open-File Report 
  98-795, map scale 1:100,000.

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  eological Survey Circular 688, 12 pp.

Youd, T.L., and Hoose, S.N., 1978, Historical ground failures in Northern 
  California triggered by earthquakes: U.S. Geological Survey Professional Paper
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Youd, T.L., and Perkins, J.B., 1987, Map showing liquefaction susceptibility of 
  San Mateo County, California:  U.S. Geological Survey, Map I-1257-G.

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  on evaluation of liquefaction resistance of soils:  Nation Center for 
  Earthquake Engineering Research Technical Report NCEER-97-0022, 276 p.



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



                          Open-File Report 00-444
                           Appendix A of Part 3
                                Version 1.0

 




                                 APPENDIX A

                        DESCRIPTION OF GEOLOGIC UNITS



                                    by

  Keith L. Knudsen(1, 2), Janet M. Sowers(1), and Robert C. Witter(1)







                            Author Affiliations

	              1 - William Lettis & Associates, Inc.
                      2 - California Division of Mines and Geology





This report is preliminary and has not been reviewed for conformity with U.S. 
Geological Survey editorial standards or with the North American Stratigraphic 
Code. Any use of trade, product, or firm names is for descriptive purposes only 
and does not imply endorsement by the U.S. Government.




                  APPENDIX A.  DESCRIPTION OF GEOLOGIC UNITS.


Map
Symbol	Unit Name and Description


	MODERN (<150 YEARS) DEPOSITS.


af	Artificial fill (historical).  Material deposited by humans other than 
	artificial fill over Bay Mud (afbm), artificial levee fill (alf), dredge
	spoils (ads), and gravel quarries and percolation ponds (gq), which are 
	mapped as separate units.  Fill may be engineered and/or non-engineered 
	material; each may occur within the same area on the map.  Most of the 
	artificial fill shown forms large highway embankments, consisting of 
	engineered fill up to approximately 100 feet thick, large earthen dams, 
	and railroad grades.  Our mapping of artificial fill on road and 
	railroad embankments is based on interpretation of topographic contours 
	on the most recent 7.5-minute U.S. Geological Survey topographic 
	quadrangles.  Fill whose thickness is less than the contour interval 
	(typically 5 to 10 ft) and fill emplaced after the topographic base maps
	were surveyed are not shown.  Small bodies of fill, such as small road 
	embankments and earthen dams for farm ponds, are not shown.  Included 
	within this unit are small areas of Holocene alluvium that are too small
	to be mapped at the scale of 1:24,000.  On the San Francisco Peninsula, 
	identification and mapping of artificial fill primarily is based on 
	previous mapping by Bonilla (1971, 1998), Schlocker, (1974), and 
	Pampeyan (1993, 1994).  Elsewhere, mapping of artificial fill is based 
	on inspection of topographic maps and aerial photographs.  

	Liquefaction susceptibility of artificial fill (af) may be very high to 
	very low depending on (1) the nature and thickness of the fill 
	materials, (2) whether the fill was engineered or non-engineered, and 
	(3) its depth of saturation.  Most fill placed in the last few decades 
	is engineered; older fill is less likely to be engineered.  A large 
	percentage of observed historical liquefaction in the area has occurred 
	in artificial fill on the margins of San Francisco Bay; however, most of
	these artificial fill bodies are included within the map unit artificial
	fill over Bay Mud (afbm).  Most artificial fill mapped in upland areas 
	or comprising highway embankments or dams is assigned a low 
	susceptibility because it is likely to be engineered and unsaturated. 
	However, many bodies of artificial fill (af) were assigned High or Very 
	High susceptibilities based on the historical occurrence of liquefaction
	within or near these bodies. 


afbm	Artificial fill over Bay Mud (historical). Material deposited by humans 
	over Bay Mud (Qhbm) or San Joaquin/Sacramento Delta mud and peat (Qhpm).
	Fill may be engineered and/or non-engineered material; each may occur 
	within the same area on the map.  This mapped artificial fill overlies 
	estuarine sediment and was placed to form new land (Goldman, 1969).  
	Mapping of artificial fill over Bay Mud is based on comparison of 
	present shorelines with those of the mid 19th century as shown by 
	Nichols and Wright (1971) and Sowers (1995, 1997, 1999), and, to a 
	limited extent, on inspection of topographic maps and aerial 
	photographs.  A line delineating the middle 19th century 
	(1850s-1860s)extent of marshland (Nichols and Wright, 1971) was used to 
	delineate the landward boundary of this unit.  Artificial fill placed 
	inland of the Nichols and Wright (1971) line was mapped as artificial 
	fill (af).  The thickness of the fill overlying estuarine sediment is 
	typically 5-20 feet.  Included within this unit are small areas of 
	estuarine deposits and Holocene alluvium that are too small to be mapped
	at the scale of 1:24,000.  Levees and dikes mapped within this unit(alf)
	are based on identification of levees on U.S. Geological Survey 
	7.5-minute topographic quadrangles.  These levee materials may not 
	differ from the underlying artificial fill over Bay Mud material (afbm).
	Other unmapped levees and dikes likely exist within mapped bodies of 
	this unit.  

	Liquefaction susceptibility is very high based on the numerous past 
	occurrences of liquefaction in this unit.  About half of all past 
	occurrences of earthquake-induced liquefaction in the San Francisco Bay 
	area occurred in artificial fill over Bay Mud.  Over 80 percent of the 
	liquefaction that was observed following the 1989 Loma Prieta earthquake
	occurred in this unit.  Most fill emplaced over Bay Mud in the last few 
	decades is engineered; older fill is less likely to be engineered.  Many
	of the reports of damage in the 1906 San Francisco earthquake and the 
	1989 Loma Prieta earthquake involved failures in older fill that 
	probably was not engineered; such fill was likely hydraulically 
	emplaced.  Where the material to be used as artificial fill was dredged 
	or suctioned from sandy areas (for example near Oakland and the Golden 
	Gate), the fill can be expected to be very susceptible to liquefaction. 
	Typically, ground-water levels in this unit are close to the ground 
	surface.  


alf 	Artificial levee fill (historical).  Constructed levees bordering 
	rivers, streams, salt ponds, sloughs, and delta islands for the purpose 
	of containing flood or tidal waters.  Some are compacted and quite firm,
	but levees built before 1965 (enactment of the Uniform Building Code) 
	are likely to be uncompacted and made of poor quality fill.  Levees 
	bordering waterways of the Sacramento/San Joaquin Delta, mudflats, and 
	large streams were first emplaced as much as 150 years ago.  The mapped 
	distribution of levee fill conforms to levees shown on the most recent 
	U.S. Geological Survey 7.5-minute topographic quadrangles.  Much of our 
	mapping of this unit was compiled from recent mapping by Russ Graymer 
	and published in Helley and Graymer (1997a, 1997b), Helley and others 
	(1994), and Brabb and others (1998a, 1998b) 

	Liquefaction susceptibility is estimated to be high for all artificial 
	levees, based on the abundance of older unengineered levees and their 
	likelihood of saturation.  Additionally, levees typically are placed in 
	areas where the substrate is highly susceptible to liquefaction.  


ads	Dredge spoils (historical).  This unit, mapped and described by Atwater 
	(1982), consists of sand, locally laminated, and subordinate silt, clay,
	and peat, that has been deposited as hydraulic dredge spoils during 
	attempts to widen, straighten, and/or deepen the Sacramento and San 
	Joaquin Rivers.  The large body of sand near the Montezuma Hills was 
	probably emplaced between 1908 and 1941 (Atwater, 1982).  This unit is 
	mapped only in a few quadrangles within the San Joaquin/Sacramento 
	Delta.  

	Liquefaction susceptibility of dredge spoils is very high based on the 
	abundance of loose sand and probable high ground-water levels.   


gq	Gravel quarries and percolation ponds (historical).  This unit consists 
	of excavations, associated spoil piles, and disturbed ground in stream 
	channels or alluvial deposits that were or are being used for the 
	purpose of extracting sand and gravel.  Because many gravel pits are 
	eventually used as recharge or percolation ponds, we include percolation
	ponds within this map unit.  

	Liquefaction susceptibility is high.


ac	Artificial stream channel (historical).  Modified stream channels 
	including straightened or realigned channels, flood control channels, 
	channels bordered by dikes or levees, and concrete canals.  In most 
	cases, artificial channels were differentiated from natural channels by 
	interpretation of 7.5-minute topographic quadrangles.  Additionally, 
	field inspection and interpretation of aerial photographs were used to 
	identify artificial channels.  Deposits within artificial channels can 
	range from nonexistent in some concrete canals, to loose, unconsolidated
	sand, gravel and cobbles, similar to deposits of modern stream channel 
	deposits (Qhc).  

	Liquefaction susceptibility is generally low, but varies with the design
	of the channel and the nature of the bank material.  Adjacent levees or 
	banks may be subject to lateral spreading into the channel if not well 
	engineered.


Qhc	Modern stream channel deposits.  Fluvial deposits within active, natural
	stream channels.  Materials consist of loose, unconsolidated, poorly to 
	well sorted sand, gravel and cobbles, with minor silt and clay.  These 
	deposits are reworked by frequent flooding and exhibit no soil 
	development.  These deposits, like most other alluvial deposits, fine 
	downstream (sediment is coarser upstream).  Mapping of modern stream 
	channels is based on topographic map inspection augmented, in places, by
	interpretation of aerial photography or orthophoto quadrangles.  Where 
	available, we reviewed early twentieth century (1914-1916) topographic 
	maps to evaluate whether stream channels shown on recent 7.5-minute maps
	have been altered since the early twentieth century.  If the channels 
	appear on recent maps as unchanged since the earlier maps, we map the 
	channel and its banks as modern stream channel deposits. Contacts 
	generally are shown near the top of the bank on either side of the 
	channel, although the deposits actually lie near the bottom of the 
	channel.  Channels of very small streams are not delineated at the 
	1:24,000 map scale; even larger streams may not be delineated where 
	mapping is at the 1:100,000 scale. 

	Liquefaction susceptibility is very high.  Tinsley and others (1985) 
	present an analysis of borehole data in the Los Angeles area that shows 
	that 76 to 81 percent of boreholes in latest Holocene alluvium contain 
	liquefiable materials, assuming ground-water levels at the surface, 
	compared to 34 to 54 percent of boreholes in earlier Holocene alluvium.  
	Matti and Carlson (1991) show that similar relations pertain in the San 
	Bernardino Valley of Southern California.  Dupr (1990), Holzer and 
	others (1994), and Mejia and others (1992) describe liquefaction along 
	the coast south and west of the 1989 Loma Prieta epicenter, most of 
	which occurred because of the presence of late Holocene, loose, granular
	sediment and high ground-water levels.  Ground-water levels typically 
	are at or near the surface in modern stream channel deposits.


	LATEST HOLOCENE (<1,000 YEARS).

Qhfy	Latest Holocene alluvial fan deposits.  Alluvial fan sediment judged to 
	be latest Holocene (<1,000 years) in age, based on records of historical
	inundation or the presence of youthful braid bars and distributary 
	channels.  Youthfulness of braid bars and distributary channels was 
	evaluated using aerial photographs and orthophotoquadrangles.  Alluvial 
	fan sediment is deposited by streams emanating from mountain canyons 
	onto alluvial valley floors or alluvial plains.  Most of the mapped 
	latest Holocene alluvial fan deposits originate from a point partway 
	down the alluvial fan slope.  The stream channel typically is incised 
	into older fan deposits near the fan apex, then gradually is less 
	incised downfan, until the stream becomes unconfined and distributes 
	young sediment across the toe of the fan.  A good example of this is the
	Alameda Creek fan in Fremont and Union City.  Sediment is moderately to 
	poorly sorted and bedded, and may be composed of gravel, sand, silt and 
	clay.  Grain size generally fines downslope.  Minimally developed soils 
	on this unit are entisols and inceptisols.

	Liquefaction susceptibility is very high because these deposits are 
	loose and generally lack cohesion.  Additionally, there have been a 
	significant number of past occurrences of liquefaction in this unit.  
	Ground water typically is less than 20 feet below the surface because 
	these deposits lie near active stream channels.  If the stream channel 
	is incised, a free face will be present and lateral spreading is likely 
	if liquefaction does occur.  However, lateral spreading is probably less
	likely in alluvial fan deposits than in laterally accreted fluvial 
	deposits (J. Tinsley, oral. com., 2000).  


Qhly  	Latest Holocene alluvial fan levee deposits.  Natural levee deposits of 
	alluvial fans judged to be latest Holocene (<1,000 years) in age based 
	on records of historical inundation.  This unit is mapped along the 
	downstream reaches of Alameda Creek, Coyote Creek, and Guadalupe River. 
	Levees are identified as long, low, sinuous ridges oriented downfan 
	("channel ridges" of Bryan, 1923 and Thomasson and others, 1960).  On 
	these very young levees, the stream often runs down the levee 
	centerline.  Levees contain coarser material than adjoining interlevee 
	areas, being composed of overbank materials dropped as the stream spills
	over its banks (Helley and others, 1979).  Soils are typically entisols 
	(fluvents).  Ground water typically is no deeper than the depth to 
	flowing water in the stream.  

	Liquefaction susceptibility is very high because of the presence of 
	loose, likely saturated deposits.  Additionally, there have been a 
	significant number of past occurrences of liquefaction in this unit.  If
	the stream channel is incised, a free face will be present and lateral 
	spreading is likely if liquefaction does occur.


Qhty  	Latest Holocene stream terrace deposits.  Stream terrace deposits judged
	to be latest Holocene (<1,000 years) in age based on records of 
	historical inundation, the identification of youthful meander scars and 
	braid bars on aerial photographs or orthophotoquadrangles, and/or 
	geomorphic position (elevation) very close to the stream channel.  
	Stream terraces are deposited as point bar and overbank deposits by 
	major streams such as the Napa River, Russian River, Coyote Creek, and 
	Alameda Creek.  Although very young stream terrace deposits also are 
	found along smaller streams, these may be too small in size to be shown 
	at the 1:24,000 and especially the 1:100,000 map scales, and therefore 
	are often included in the modern stream channel (Qhc) or Holocene stream
	terrace (Qht) map units.  Stream terrace sediment includes sand, gravel,
	silt, and minor clay, is moderately to well sorted, and is moderately to
	well bedded. 

	Liquefaction susceptibility is very high based on the abundance of 
	sandy, cohesionless sediment, high ground-water levels, and the presence
	of a free face at the channel banks, which makes lateral spreading 
	likely.  The relative lateral extent of many stream terrace deposits 
	makes these deposits more likely to experience lateral spreading than 
	alluvial fan deposits.  


Qhay	Latest Holocene alluvial deposits, undifferentiated.  Fluvial sediment 
	judged to be latest Holocene (<1000 years) in age based on records of 
	historical inundation, the identification of youthful meander scars and 
	braid bars on aerial photographs or orthophotoquadrangles, or geomorphic
	position very close in elevation to the stream channel.  This sediment 
	was deposited on modern flood plains, active stream channels, active 
	alluvial fans, and flood-prone areas.  Deposits are loose sand, gravel, 
	silt and clay.  This unit is mapped in areas that historically have been
	inundated by sediment-bearing water.  Latest Holocene alluvial deposits 
	may include terrace deposits (Qhty), deposits of the active stream 
	channel (Qhc), alluvial fan deposits (Qhfy), basin deposits (Qhb), and 
	levee deposits (Qhly).  However, the small size of individual deposits 
	of these map units prevented differentiation at the map scales used in 
	this project.  Typical soils developed on these deposits are entisols 
	(fluvents).  

	Liquefaction susceptibility is very high based on the presence of loose 
	cohesionless sediment near the active stream channel.  Proximity to the 
	active stream channel indicates that (1) ground-water levels likely are 
	close to the surface, and (2) a free face may be present.  


Qhbs	Latest Holocene beach sand. This unit includes active beaches in coastal
	environments.  Beach deposits typically are well sorted fine to coarse 
	sand with some fine gravel.  Where the beach is adjacent to a seacliff, 
	beach sediment may form a veneer over a bedrock platform.  In places, 
	low unstable dunes and/or sandy islands may be included within this map 
	unit.  

	Liquefaction susceptibility is very high because beach sand is well 
	sorted, saturated, loose sand. 


	LATE HOLOCENE (<3,000 YEARS).


Qhfp	Late Holocene alluvial floodplain deposits, undifferentiated. Atwater 
	(1982) mapped this unit in the western San Joaquin and Sacramento 
	valleys to indicate a time-transgressive floodplain of the San Joaquin 
	River.  This unit is mapped on the Clifton Court Forebay and Woodward 
	Island 7.5-minute quadrangles.  Most, if not all, of this area has been 
	inundated historically during large floods.  Part of this area was 
	covered historically with tidal-wetland peat, but underlying deposits 
	have since been exhumed by wind erosion.  Much of the area mapped by 
	Atwater (1982) as late Holocene alluvial floodplain deposits is now 
	protected by artificial levees (alf) and is farmed.  These deposits are 
	younger than, and lap onto, the Antioch-Oakley dune field, which may be 
	coeval with the upper member of the Modesto Formation (Atwater, 1982) 
	and some deposits mapped as the Merritt Sand by previous researchers.  
	This unit includes abandoned oxbows, channels and interdistributary 
	basins, flood basins and basin rims, distal alluvial fans, and low 
	natural levees adjacent to the San Joaquin River.  This unit generally 
	slopes downstream at low gradients parallel to the San Joaquin River.  
	Atwater's (1982) mapping of this unit is adopted with very few 
	modifications.  Soils formed on this unit include the Columbia, 
	Sacramento, and Ramada soils of Retzer and others (1951). 

	Liquefaction susceptibility is very high because of the recency of 
	inundation, high ground-water levels, and proximity to active stream 
	channels.  


Qhfb	Late Holocene flood-basin deposits  This unit (<3,000 years), mapped and
	described by Atwater (1982), formed in the supratidal reaches of basins 
	flanking the Sacramento River and in interdistributary basins cut off 
	from tidal waters.  Atwater (1982) mapped this map unit on four 
	quadrangles: Courtland, Dozier, Liberty Island and Rio Vista within the 
	nine-county area.  Deposits are firm to stiff silty clay, clayey silt, 
	and silt, commonly with CaCO3 nodules and locally with black spherules 
	(Mn and/or Fe oxides).  Native vegetation was dominated by Scirpus 
	acutus (tule).  The deposits laterally grade into peaty mud and mud of 
	tidal wetlands.  Locally, the deposits are veneered with silty, 
	reddish-brown alluvium of historic age, some of which may have resulted 
	from hydraulic mining in the Sierra Nevada during the late 1800s.  Cosby
	(1941) mapped this unit as Sacramento and Columbia-over-Sacramento 
	soils.

	Liquefaction susceptibility is high because of the recency of 
	inundation, high ground-water levels, and proximity to active stream 
	channels.  Much of the sediment mapped within this unit is fine grained,
	and is not likely to liquefy.  However, the deposits' youthfulness, high
	ground-water levels and presence of lenses and sheets of sandy material 
	indicate a high susceptibility to liquefaction in places.  


	HOLOCENE (<10,000 YEARS).


Qhds	Holocene dune sand. This unit includes active dunes along with recently 
	stabilized dunes in coastal environments.  Dune sand typically is very 
	well sorted fine to medium sand.  This unit is mapped in only a few 
	places, typically near beaches, where Holocene age for much of the 
	deposit is likely.  Large latest Pleistocene dune fields like the 
	Antioch-Oakley dunes, the Merritt Sand, and most of the dunes covering 
	the northern San Francisco Peninsula, which are mapped as latest 
	Pleistocene to Holocene dune sand (Qds), likely contain areas of 
	unmapped Holocene dune sand.  Typical soils developed on this unit 
	(Qhds) are inceptisols.

	In areas of high ground water or perched water conditions, such as 
	beaches or dunes near water bodies, liquefaction susceptibility is very 
	high.  


Qhbm	Holocene San Francisco Bay Mud.  Sediment deposited at or near sea level
	in the San Francisco Bay estuary that is presently, or was historically 
	tidal marsh, mud flat or bay bottom.  Bay Mud sediment typically has low
	bulk density and includes silt, clay, peat, and fine sand (Atwater and 
	others, 1977).  This unit is time-transgressive and generally occupies 
	the area between the modern shoreline and the historical limits of tidal
	marsh, as shown on the compilations by Nichols and Wright (1971), San 
	Francisco Estuary Institute (1998), and Sowers (1995, 1997, 1999) of 
	historical surveys of tidal marshlands circa 1850.  We include areas 
	that are presently, or were recently, used as salt evaporation ponds 
	within this unit.  Also included within this map unit are small areas of
	artificial fill and Holocene alluvium too small to be mapped at the map 
	scales used in this project.  Especially relevant to the evaluation of 
	liquefaction susceptibility are the many small marsh channels that are 
	too small to map, yet likely contain sandy substrates and may be more 
	susceptible to liquefaction than the silt, clay and peat of the marsh 
	deposits.  Soils developed on estuarine deposits typically are 
	histosols, aquic entisols or mollisols.  Bay Mud is mainly latest 
	Holocene in age with many areas presently subject to deposition and 
	flooding.  Some areas have been diked for farming, salt evaporators, or 
	other purposes.  Bay Mud deposits thin landward and may be as thick as 
	40 m along the bay margin (Rogers and Figuers, 1991).  This unit is 
	texturally and genetically similar to Holocene San Joaquin/ Sacramento 
	Delta mud and peat, which we map upstream of the confluence between the 
	Sacramento and San Joaquin rivers.  

	Liquefaction susceptibility is high due to high ground-water levels 
	(often tidally influenced) and the presence of sand lenses within the 
	mud and peat.  The mud itself is unlikely to liquefy due to the 
	abundance of clay.  Estuarine sediment near the mouths of major streams,
	such as Alameda Creek, is probably the most susceptible to liquefaction 
	because the streams regularly deliver large volumes of sand and silt to 
	the estuary.  About 5 percent of all observed occurrences of 
	 in the San Francisco Bay Area have occurred within this unit.  


Qhdm	Holocene San Joaquin/Sacramento Delta mud and peat. Sediment deposited 
	at or near sea level in the Sacramento/San Joaquin Delta that is 
	presently, or was once tidal marsh.  Mapping of this unit is based on 
	Atwater's (1982) mapping of "Qpm - Peat and mud of tidal wetlands and 
	waterways".  Delta peat and mud typically have low bulk density and 
	include silt, clay, and peat with minor sand (Atwater, 1982).  This unit
	generally occupies historical lowlands (tidal wetlands and waterways) 
	that are now dry because of the construction of dikes and levees.  Delta
	mud is late Holocene in age with many areas still subject to modern 
	deposition and flooding if levees are breeched.  Much of the area mapped
	as Delta mud and peat is now below sea level because of historical 
	subsidence and deflation of now unsaturated marsh surfaces.  Soils are 
	histosols, aquic entisols or mollisols and are mapped as Correra, 
	Venice, Staten, Egbert, Ryde, Burns and Roberts soil series of Cosby 
	(1941, in Atwater, 1982). Also included within this unit are small areas
	of artificial fill too small to be mapped at the scale of this project. 

	Liquefaction susceptibility is high because ground water is near the 
	surface and there are many lenses of sand within the mud and peat.  


Qhb	Holocene basin deposits.  Sediment that accumulates from standing or 
	slow moving water in topographic basins.  Basin deposits consist of 
	fine-grained alluvium with horizontal stratification.  These deposits 
	can be interbedded with lobes of coarser alluvium from streams that 
	drain into the basin.  Interbeds of peat may also be present. 
	Identification of basin deposits is based on surface morphology, 
	topographic position, and soil type.  This unit is similar to flood 
	basin deposits (Qhfb) of the Sacramento/San Joaquin Delta area (Atwater, 
	1982), and is similar in texture to Holocene alluvial fan, fine facies 
	(Qhff) deposits.  Ground water is high, often at the surface, especially
	during the rainy season.  Many basins contain, or historically 
	contained, seasonal wetlands, for example, Lake Elizabeth in Fremont and
	Tulare Lake in the Pleasanton area.  Typical soil series developed on 
	basin deposits include Alamitos, Sunnyvale, Willows, Sycamore, and Clear
	Lake.  These soils are clay rich with mottled subsoils, and may be 
	somewhat saline or calcareous. 

	Liquefaction susceptibility is high.  Although these deposits contain 
	abundant clay, they also may contain layers of sand and silt.  In a 
	fluvial environment, we expect the distribution of sand to be irregular 
	and discontinuous.  Thus, we assume that layers of liquefiable material 
	may be present within basins.  Ground water at or near the ground 
	surface makes liquefaction of surficial basin deposits possible.


Qhf	Holocene alluvial fan deposits.  Sediment deposited by streams emanating
	from mountain canyons onto alluvial valley floors or alluvial plains as 
	debris flows, hyperconcentrated mudflows, or braided stream flows.  
	Alluvial fan sediment includes sand, gravel, silt, and clay, and is 
	moderately to poorly sorted, and moderately to poorly bedded.  Sediment 
	clast size and general particle size typically decreases downslope from 
	the fan apex.  Many Holocene alluvial fans exhibit levee/interlevee 
	topography, particularly the fans associated with creeks flowing west 
	from the eastern San Francisco Bay Area hills [See Holocene alluvial fan
	levee deposits (Qhl) below].  Alluvial fan surfaces are steepest near 
	their apex at the valley mouth, and slope gently basinward, typically 
	with gradually decreasing gradient.  Alluvial fan deposits are 
	identified primarily on the basis of fan morphology and topographic 
	expression.  Holocene alluvial fans are relatively undissected, 
	especially when compared to older alluvial fans.  In places, Holocene 
	deposits may be only a thin veneer over Pleistocene deposits.  Soils are
	typically entisols, inceptisols, mollisols, and vertisols.  Greater than
	5 percent of the nine-county San Francisco Bay Area is covered by 
	Holocene alluvial fan deposits; it is the most extensive Quaternary map 
	unit in the region.  

	Liquefaction susceptibility is moderate where ground water is within 30 
	feet of the surface, which we believe to be the case for most Holocene 
	alluvial fan deposits.  Alluvial fan deposits are judged to be less 
	susceptible to surface deformation from liquefaction than terrace 
	deposits (Qht) of the same age because: (1) alluvial fan deposits have 
	relatively poor sorting and coarse grain size; (2) alluvial fan deposits
	are typically lenticular, thus, liquefaction within alluvial fan 
	deposits may be confined to small "pockets" of susceptible material; and
	(3) stream terrace deposits commonly have a free face as one boundary, 
	making lateral spreading a hazard.  Where an active channel is present 
	but is not mapped through the fan because of the map scale, the 
	liquefaction susceptibility may be underestimated.  


Qhl	Holocene alluvial fan levee deposits.  Natural levee deposits of 
	alluvial fans are formed by streams that overtop their banks and deposit
	sediment adjacent to the channel.  Mapping of these deposits is based on
	interpretation of topography; levees are identified as long, low ridges 
	oriented down fan ["channel ridges" of Thomasson and others (1960)].  
	They contain coarser material than adjoining interlevee areas, 
	especially adjacent to creek banks where the coarsest material is 
	deposited during floods (Helley and others, 1979).  Levee deposits are 
	loose, moderately to well sorted sand, silt and clay (Helley and 
	Wesling, 1989).  Soils are typically entisols, inceptisols, mollisols, 
	and vertisols.  

	Liquefaction susceptibility is moderate, similar to Holocene alluvial 
	fan deposits.  Where streams are incised, these deposits may be 
	susceptible to lateral spreading.  


Qhff  	Holocene alluvial fan deposits, fine facies.  Fine-grained alluvial fan 
	and flood plain overbank deposits laid down in very gently sloping 
	portions of the alluvial fan or valley floor.  Slopes in these distal 
	alluvial fan areas are generally less than or equal to 0.5 degrees, 
	soils are clay rich, and ground water is within 3 meters of the surface.
	Deposits are dominated by clay and silt, with interbedded lobes of 
	coarser alluvium (sand and occasional gravel).  Deposits of coarse 
	material within these fine-grained materials are elongated in the 
	downfan or down valley direction.  These lobes are potential conduits 
	for ground water flow.  The surface contact with relatively coarser 
	facies, fan (Qhf) and levee (Qhl), is both gradational and 
	interfingering, thus is dashed.  These deposits are similar to "basin 
	deposits" mapped by Helley and Graymer (1997a, 1997b) and Helley and 
	others (1994).  Typical soil series developed on this unit include 
	Sunnyvale, Orestimba, Clear Lake, Pescadero, Pacheco and Willows.  These
	soils are clay rich with mottled or calcareous subsoils. 

	Liquefaction susceptibility is high based on shallow ground water and 
	the presence of lenses of coarse sandy material.  


Qhfe	Holocene fine-grained alluvial fan-estuarine complex deposits.  Deposits
	that form in the transition zone from distal fan and basin environments 
	to the estuarine environment.  This unit is mapped along the southern 
	San Francisco Bay margin between the Guadalupe River and Coyote Creek 
	within the Milpitas 7.5-minute quadrangle.  The deposits represent a 
	transition zone from fluvial sand, silt, and clay (Qhf, Qhfy, Qhl, Qhly,
	Qhff) to Bay Mud (Qhbm).  Coarser fluvial sediment, some of which may be
	historical, typically forms a veneer over the finer sediment (Qhff) and 
	may overlie or interfinger with Bay Mud.  Bay Mud in this area is 
	distinguished from fine grained alluvial fan sediment (Qhff) by its 
	compressibility, high water content, and peat content (Sarna, 1967).

	Discontinuous sloughs oriented perpendicular to the bay margin are 
	typical of this zone and are interpreted to be segments of abandoned 
	creek channels whose upper reaches are filled by recent fluvial 
	sediment.  The lower reaches are maintained by a combination of 
	ground-water seepage and tidal influx.  This unit includes a tongue of 
	Bay Mud mapped by Sarna (1967) that extends up the Guadalupe River.  
	Borings in this area indicate the presence of both Bay Mud and very 
	young fluvial sediment.  We do not, however, include within this map 
	unit a tongue of Bay Mud mapped by Sarna (1967) along Coyote Creek.  
	Borings in this area are concentrated along the creek channel where 
	tidal influx within the channel itself may be responsible for the 
	deposition of Bay Mud.  The area on either side of the channel is mapped
	as a natural levee (Qhly), based on the shape of the 10-foot contour 
	line and the presence of Mocho loam, an alluvial soil (Gardner and 
	others, 1958).

	Soils within this transition zone are strongly to moderately saline or 
	alkaline; the native vegetation historically included salt grass and 
	pickleweed (Goals Project, 1999).  Soil series associated with this zone
	include the Alviso clay, tidal marsh, and the Mocho loam and fine clay 
	loam over basin clays (Gardener and others, 1958).  Ground water is 
	tidally influenced.

	Liquefaction susceptibility is high based on the presence of shallow 
	ground water, historical inundation, and lenses of coarse material.  


Qht	Holocene stream terrace deposits.  Stream terrace deposits that were 
	deposited in point bar and overbank settings.  Terrace deposits include 
	sand, gravel, silt, and minor clay, and are moderately to well sorted, 
	and moderately to well bedded.  Typically, this unit is mapped where 
	relatively smooth, undissected terraces are less than 25 to 30 ft above 
	the active channel.  Soils are typically entisols, inceptisols, and 
	mollisols.  Ground-water levels are generally within 10 ft of the 
	surface, especially during the wet winter months.  Terrace deposits that
	are too small in extent to be shown at the map scale, such as those 
	along small creeks, are included within the undifferentiated alluvium 
	(Qha and Qa) mapping units.

	Liquefaction susceptibility is high because of the presence of loose, 
	granular deposits and shallow ground water.  Should liquefaction occur, 
	the presence of a free face and laterally extensive point bar deposits 
	makes lateral spreading likely.  Overbank deposits, which typically 
	overlie point bar deposits, are not as susceptible to liquefaction, or 
	to lateral spreading should liquefaction occur, as point bar deposits.


Qha	Holocene alluvium, undifferentiated.  Alluvium deposited in fan, 
	terrace, or basin environments.  This unit is mapped where separate 
	types of alluvial deposits could not be delineated either due to complex
	interfingering of depositional environments or the small size of the 
	area.  Typically, undifferentiated alluvium is mapped in relatively 
	flat, smooth valley bottoms of small- to medium-sized drainages.  The 
	planar and smooth geomorphic surfaces, with little to no dissection, 
	indicate that there has been little post-stabilization 
	modification/dissection of the surface; thus, deposits with smooth 
	surfaces are interpreted to be Holocene in age.  Undifferentiated 
	Holocene alluvial deposits probably are intercalated sand, silt, and 
	gravel that are poorly to moderately sorted.  Soils are entisols, 
	inceptisols, vertisols, and mollisols.  

	Liquefaction susceptibility is high to moderate, based on: (1) 
	historical liquefaction occurrences (for example Colma Creek valley); 
	(2) the presence of undifferentiated late Holocene channels and 
	deposits; (3) high ground-water levels; (4) the presence of small 
	unmapped, potentially unengineered bodies of artificial fill; and (5) a 
	combination of the susceptibility assignments for channel, fan, terrace,
	and basin deposits (Qhc, Qhf, Qht, and Qhb).  However, for purposes of 
	this project, we assume that the liquefaction susceptibility of this 
	unit is high.


	HOLOCENE TO LATEST PLEISTOCENE (<30,000 YEARS)


Qds	Latest Pleistocene to Holocene dune sand.  Very well sorted fine to 
	medium grained eolian sand (<30,000 years).  Holocene sand may 
	discontinuously overlie latest Pleistocene sand, both of which may form 
	a mantle of varying thickness over older materials.  Most of these 
	deposits are thought to be associated with latest Pleistocene to early 
	Holocene low sea level stands and subsequent transgression, during which
	large volumes of fluvial and glacially derived sediment were blown into 
	dunes (Atwater and others, 1977).  The deposits include the Merritt Sand
	in the Oakland area, the sand dunes that cover much of the northern San 
	Francisco Peninsula, and the Antioch-Oakley dune field that Atwater 
	(1982) maps as "Qm2e - Eolian deposits of the upper member of the 
	Modesto Formation".  These deposits (Qds) consist of fine to medium sand
	that is semiconsolidated and weakly cemented.  

	The Oakley-Antioch dune field is composed of materials having both 
	Sacramento River and San Joaquin River origins.  Atwater (1982) suggests
	that the dunes in the Antioch-Oakley dune field are likely 10,000 to 
	14,000 years old.  In many areas, leveling of agricultural fields, 
	fluvial reworking and inundation by alluvial fan materials has obscured 
	the original dune morphology of these deposits.  Soils formed on these 
	deposits are typically entisols, and include the Piper and Oakley soil 
	series of Cosby (1941).  Depth to ground water varies, primarily with 
	the height of the dune, but is generally greater than ten feet.

	Liquefaction susceptibility is generally low, but may be high locally 
	where ground water is shallow and sand is Holocene in age; therefore, we
	have assigned these deposits moderate liquefaction susceptibility.  
	Deposits of this unit hosted about 4 percent of all observed occurrences
	of liquefaction.  However, there were no reports of liquefaction within 
	the Merritt Sand for either the 1906 or 1989 earthquakes (Youd and 
	Hoose, 1978; Seed and others, 1990).  


Qb	Latest Pleistocene to Holocene basin deposits.  Sediment deposited in 
	topographic lows, such as a closed or semi-enclosed basin.  These areas 
	have a high ground-water table and soils characterized as poorly 
	drained.  Deposits are generally clay rich.  This unit is mapped in the 
	axis of Kenwood valley where the presence of both latest Pleistocene and
	Holocene deposits is suggested by a range in soil development that 
	includes vertisols (relatively youthful clay rich soils) and durixeralfs
	(mature soils having a B horizon and hardpan).

	Liquefaction susceptibility is low because of the fine-grained nature of
	these deposits.


Qf	Latest Pleistocene to Holocene alluvial fan deposits.  This unit is 
	mapped on gently sloping, fan-shaped, relatively undissected alluvial 
	surfaces where the age of deposits might be either latest Pleistocene or
	Holocene in age or where the deposits consist of thin "patches" of 
	Holocene sediment overlying latest Pleistocene alluvial fan sediment.  
	Fan sediment includes sand, gravel, silt, and clay, and is moderately to
	poorly sorted, and moderately to poorly bedded.  Soils formed on these 
	deposits are typically mollisols, and alfisols.  This unit includes 
	active stream channels that are too narrow to show separately at the map
	scales used in this project.  

	Liquefaction susceptibility is generally low.  Ground water is assumed 
	to be greater than ten feet below the surface.  Sediment in stream 
	channels that have not been differentiated within this unit may be 
	moderately susceptible to liquefaction. 


Ql	Latest Pleistocene to Holocene alluvial fan levee deposits.  Levee 
	deposits on smooth, relatively undissected alluvial fans where deposit 
	age is uncertain.  This unit is mapped on the southern part of the 
	Alameda Creek fan.  Here, although fan geomorphology is relatively 
	youthful, a pre-Holocene age is suggested by the presence of a 
	fault-related ridge that now blocks deposition on this part of the fan 
	by Alameda Creek, as well as development of mollisols and alfisols on 
	the levee surface.

	Liquefaction susceptibility is low.  Ground water is assumed to be 
	greater than ten feet below the surface.  


Qt	Latest Pleistocene to Holocene stream terrace deposits.  This unit is 
	mapped on relatively flat, undissected stream terraces where deposit age
	is uncertain.  Terrace deposits include sand, gravel, and silt, with 
	minor clay, and are moderately to well sorted, and moderately to well 
	bedded.  Soils are typically inceptisols, mollisols, and alfisols.  
	Ground-water depth is variable, but is generally less than 30 feet.  
	This unit may include active stream channels that are too narrow to show
	separately at the map scales of this project.  Sediment in the stream 
	channel is dominantly gravel and sand.

	Liquefaction susceptibility is low to high, where ground water is within
	10 feet of the surface.  The range in susceptibility is a reflection of 
	the range or uncertainty in age of the terrace deposits.  However, 
	overall, the unit is assumed to have a moderate liquefaction 
	susceptibility.  Liquefaction susceptibility in undifferentiated 
	channels within these deposits, especially in point bar deposits, is 
	high.


Qa	Latest Pleistocene to Holocene alluvium, undifferentiated.  This unit is
	mapped in small valleys where separate fan, basin, and terrace units 
	could not be delineated at the scale of this mapping, and where deposits
	might be of either latest Pleistocene or Holocene age.  The unit 
	includes flat, relatively undissected fan, terrace, and basin deposits, 
	and small active stream channels.  Soils formed on these deposits are 
	mollisols, alfisols and vertisols.

	Liquefaction susceptibility is moderate.  Ground-water depth is 
	variable, but is generally less than 20 feet.  The moderate 
	susceptibility assignment is a reflection of uncertainties and local 
	variability in the both the nature and age of these deposits.


	LATEST PLEISTOCENE (10,000 TO ~30,000 YEARS).


Qpb	Latest Pleistocene basin deposits.  This unit was mapped by Atwater 
	(1982), who describes it as follows: "Older alluvium of Putah Creek is 
	widely but sparsely exposed at the toe of the Putah Creek fan, most 
	commonly in basins between stream-built ridges of younger alluvium.  In 
	the Saxon 7.5-minute quadrangle, ..., it locally forms hills as much as 
	5 ft high and 100 to 1000 ft across, conceivably the remnants of 
	steam-built ridges or an interglacial flood basin similar to Yolo 
	Basin."  Soils formed on this unit are San Ysidro and Antioch series 
	(Bates, 1977).

	Liquefaction susceptibility is low based on the age of the deposits and 
	their fine-grained texture.


Qpf	Latest Pleistocene alluvial fan deposits.  This unit is mapped on 
	alluvial fans where latest Pleistocene age is indicated by greater 
	dissection than is present on Holocene fans, and/or the development of 
	alfisols.  Latest Pleistocene alluvial fan sediment was deposited by 
	streams emanating from mountain canyons onto alluvial valley floors or 
	alluvial plains as debris flows, hyperconcentrated mudflows, or braided 
	stream flows.  Alluvial fan sediment typically includes sand, gravel, 
	silt, and clay, and is moderately to poorly sorted, and moderately to 
	poorly bedded.  Sediment clast size and general particle size typically 
	decreases downslope from the fan apex.  Latest Pleistocene alluvial fan 
	sediment is approximately 10 percent denser than Holocene alluvial fan 
	sediment and has penetration resistance values about 50 percent greater 
	than values for Holocene alluvial fan sediment (Clahan and others, 
	2000).  Pleistocene alluvial fans may be veneered or incised by thin 
	unmapped Holocene alluvial fan deposits.  Along the west-facing hills of
	Oakland and Berkeley, where latest Pleistocene alluvial fan deposits are
	mapped, the age of these deposits is not well constrained and the 
	deposits may actually be a combination of early to late Pleistocene 
	alluvial fan and thin pediment deposits, and latest Pleistocene alluvial
	fan deposits.  

	Liquefaction susceptibility is low.  Ground-water levels are variable, 
	but generally are more than 20 feet below the surface.  Deposits 
	typically are very stiff to hard or medium dense to very dense (Haydon 
	and others, 1999; Clahan and others, 2000).  


Qpt	Latest Pleistocene stream terrace deposits. This unit is mapped on 
	relatively flat, slightly dissected stream terraces where latest 
	Pleistocene age is indicated by the development of alfisols and height 
	of the terrace above flood level.  Terrace sediment includes sand, 
	gravel, silt, with minor clay, and is moderately to well sorted, and 
	moderately to well bedded.  Terrace sediment typically was deposited in 
	point bar and overbank settings and has since been elevated above the 
	creek bottom by incision of the streambed.  Latest Pleistocene terrace 
	deposits that are too small in extent to be shown at the map scale, such
	as those along small creeks, may be included within the undifferentiated
	latest Pleistocene and latest Pleistocene to Holocene alluvial mapping 
	units (Qpa and Qa).

	Liquefaction susceptibility is low because of the age of the deposits 
	and the likelihood that ground water is relatively deep.  Should 
	liquefaction occur, the presence of a free face makes lateral spreading 
	likely.  


Qpa	Latest Pleistocene alluvium, undifferentiated.  This unit is mapped on 
	gently sloping to level alluvial fan or terrace surfaces where latest 
	Pleistocene age is indicated by depth of stream incision, development of
	alfisols, and lack of historical flooding.  Undifferentiated latest 
	Pleistocene alluvium is mapped in small valleys where separate fan, 
	basin, and terrace units could not be delineated at the mapping scale of
	this project.  These undifferentiated latest Pleistocene alluvial 
	deposits probably are intercalated sand, silt, and gravel that are 
	poorly to moderately sorted.  

	Liquefaction susceptibility is low because of the age of the deposits 
	and the probability that ground water is relatively deep (10 to 30 
	feet). 


	PLEISTOCENE (10,000 to 1.6 MYRS).


Qmt	Pleistocene marine terrace deposits.  Deposits on uplifted marine 
	abrasion platforms along the Pacific Ocean.  In many cases, we have not 
	evaluated the age of the deposits (for example late versus middle or 
	early Pleistocene), however, for much of the western San Francisco 
	Peninsula, we have assigned relative ages by numbering the deposits 1 
	through 4.  Sediment deposited on the strath platforms is typically 
	greater than 10 feet thick and consists of moderately to well sorted, 
	moderately to well-bedded sand and gravel, which may be locally 
	fossiliferous.  We compiled and modified mapping of marine terrace 
	deposits by Weber and others (1993), Jack (1969), and unpublished 
	mapping by K. Lajoie in the southwestern part of the San Francisco 
	Peninsula south to Santa Cruz County.  Unpublished mapping by K. Lajoie 
	also was used in mapping marine terraces along the Marin County and 
	Sonoma County coasts.  

	Liquefaction susceptibility is low.  Ground water is typically deeper 
	than 20 feet, though areas may have perched ground water where marine 
	sediment overlies relatively impermeable bedrock.  Marine terrace 
	sediment is typically too dense to liquefy.  


	EARLY TO LATE PLEISTOCENE (~30,000 to 1.6 MYRS).


Qop	Early to late Pleistocene pediment deposits.  Alluvial deposits that 
	form a thin veneer on broad, planar erosional surfaces cut on bedrock or 
	older sediment.  These pediments typically occur tens to hundred(s) of 
	meters above the present stream channel and are extremely dissected.  
	Bedrock and/or older sediment are exposed by dissecting channels at 
	depths less than 5 meters beneath the alluvium, and, in places, only 
	sparse sediment may remain from the original deposits.  These deposits 
	are mapped primarily based on their geomorphic expression as interpreted
	from topographic maps.  Soils formed on these deposits typically are 
	well developed, and include alfisols and ultisols.

	Liquefaction susceptibility is very low because of the age of the 
	deposits and their density.  Because these deposits are typically at 
	least tens of feet above present stream channels, ground water commonly 
	is not present in these deposits.


Qof 	Early to late Pleistocene alluvial fan deposits.  Moderately to deeply 
	dissected alluvial deposits capped by alfisols, ultisols, or soils 
	containing a silicic or calcic duripan.  Early to late Pleistocene 
	alluvial fan sediment was deposited by streams emanating from mountain 
	canyons onto alluvial valley floors or alluvial plains as debris flows, 
	hyperconcentrated mudflows, or braided stream flows.  Because of the age
	of these deposits, the streams responsible for deposition of mapped 
	bodies of early to late Pleistocene alluvial fan sediment may have 
	evolved and no longer be readily evident in today's topography.  
	Alluvial fan sediment typically includes sand, gravel, silt, and clay, 
	and is moderately to poorly sorted, and moderately to poorly bedded.  
	This unit differs from undifferentiated early to late Pleistocene 
	alluvium (Qoa) in that some original fan surface morphology is 
	preserved.  

	Liquefaction susceptibility is very low because of the age and density 
	of the sediment as well as large depths to ground water.


Qot	Early to late Pleistocene stream terrace deposits.  Moderately to deeply
	dissected alluvial terrace deposits capped by alfisols, ultisols, or 
	soils containing a silicic or calcic hardpan.  Terrace sediment includes
	sand, gravel, and silt, with minor clay, and is moderately to well 
	sorted, and moderately to well bedded.  Terrace sediment typically was 
	deposited in point bar and overbank settings and has since been elevated
	above the creek bottom by incision of the streambed.  This unit differs 
	from Qoa in that some terrace surface morphology is preserved.  
	Liquefaction susceptibility is very low because of the age and density 
	of the sediment.

Qoa	Early to late Pleistocene alluvial deposits, undifferentiated.  
	Moderately to deeply dissected alluvial deposits capped by alfisols, 
	ultisols, or soils containing a silicic or calcic hardpan.  Topography 
	often consists of gently rolling hills with little or none of the 
	original planar alluvial surface preserved.  Deposits mapped within this
	map unit can include alluvial fan, stream terrace, basin and channel 
	deposits.  This unit includes the Colma Formation on the San Francisco 
	Peninsula (Bonilla, 1971; Schlocker, 1974), which has been described as 
	a marine, estuarine and fluvial, unconsolidated fine to medium sand with
	silt and clay.  It also includes Pliocene to Pleistocene deposits shed 
	off the flanks of Mt Diablo that have been previously mapped by Helley 
	and Graymer (1997a and b).  

	Liquefaction susceptibility is very low because of the age and density 
	of the sediment.


br	Pre-Quaternary deposits and bedrock, undifferentiated.  Primarily 
	Jurassic to Pliocene sedimentary, metamorphic, volcanic and plutonic 
	rocks, and poorly consolidated Tertiary sediment.  Includes some 
	Pliocene to Pleistocene sedimentary units such as the Glen Ellen 
	Formation, Santa Clara Formation, Livermore gravels, and Merced 
	Formation.  Unit also includes landslides, talus, other bodies of 
	colluvium, and small stream channel deposits in bedrock that could not 
	be delineated at the map scales used in this project.

	Liquefaction susceptibility is very low.  Stream channels within areas 
	mapped as bedrock may contain small areas of Holocene deposits; 
	susceptibility of these isolated deposits may be low to very high.  





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



                          Open-File Report 00-444
                            Appendix B of Part 3
                                Version 1.0

 




                                APPENDIX B

               RELATION OF SOIL SERIES TO QUATERNARY UNITS



                                    by

                Janet M. Sowers(1) and Keith L. Knudsen(1, 2)





                            Author Affiliations

	           1 - William Lettis & Associates, Inc.
                   2 - California Division of Mines and Geology





This report is preliminary and has not been reviewed for conformity with U.S. 
Geological Survey editorial standards or with the North American Stratigraphic 
Code. Any use of trade, product, or firm names is for descriptive purposes only 
and does not imply endorsement by the U.S. Government.



                                APPENDIX B: 
              RELATION OF SOIL SERIES TO QUATERNARY UNITS

Specific soil series typically are associated in the region with Quaternary 
deposits of specific age and environment of deposition.  We used published soil 
information to help understand the age and nature of the Quaternary deposits.  
The first column in the following table lists the soil series known to occur on 
alluvial deposits in the San Francisco Bay Region, as mapped and described by 
soil scientists of the U. S. Department of Agriculture.  The second column shows
the soil classification, or a brief description of the soil, based on the soil 
survey.  The third column shows the Quaternary map units that are associated 
with each of the soil series in this report.  These associations are based on 
our interpretation of the description of soil-profile development, physical 
properties, parent material, and geomorphic setting presented in the soil 
surveys, and our observations of the typical geomorphic position occupied by 
each soil.  After establishing these associations we were able to use the soil 
survey maps as a tool in interpreting the Quaternary geology.  Soil-profile 
development was especially helpful in assigning age estimates to Quaternary 
deposits.  Soil series boundaries were moderately helpful in defining Quaternary
geologic contacts, but were less important than the interpretation of topography
and aerial photography.  For additional information on soil taxonomy or methods 
and nomenclature used by soil scientists, please refer to "Keys to Soil 
Taxonomy" (U.S. Department of Agriculture, Soil Survey Staff, 1994).  


1. Santa Clara area 

Soil survey reference: Gardner, R. A., Harradine, F. F., Hargreaves, G. H., 
Retzer, J. L., Bartholomew, O. F., and Glassey, T. W., 1958, Soil Survey of the 
Santa Clara Area, California, U. S. Department of Agriculture, Soil Conservation
Service, Series 1941,  No. 17, 202 p., 2 map sheets at 1:50,000 scale.

Quadrangles covered: Milpitas, Mountain View, San Jose East, San Jose West, 
Cupertino, Los Gatos, Santa Teresa Hills, and parts of  Lick Observatory, 
Calaveras Reservoir, Morgan Hill, Palo Alto, Mindego Hill, Castle Rock Ridge, 
and Loma Prieta.

Soil Series	Soil description		Typical Quaternary unit(s)
Alamitos	Black clay with mottled 	Qhfe, Qhff
		subsoil, often in a 
		drained freshwater marsh	Qhfe, Qhff

Alviso		Saline clay at tidal marsh 
		margin with calcareous subsoil

Azule 		Silty clay on old terraces, 	Qoa, Qof
		especially the Santa Clara 
		formation

Bayshore	Calcareous clay loam at 	Qhfe, Qhff
		basin margins, high groundwater

Campbell	Dark gray clay loam to silty 	Qhf , Qhff
		clay with mottled calcareous 
		subsoil

Castro		Dark gray clay to silty clay 	Qhf, Qhff
		with lime hardpan and mottling 
		in the subsoil

Clear Lake	Dark gray clay with calcareous 	Qhf, Qhff	
		subsoil

Cropley		Dark gray gravelly clay loam 	Qhf
		to clay with calcareous subsoil

Dublin		Dark gray clay to clay loam, 	Qhf
		non-calcareous subsoil

Edenvale	Dark gray clay formed from 	Qhf
		alluvium derived from basic 
		igneous rocks

Milpitas	Brown acid loam to clay loam 	Qpa, Qoa
		over reddish brown claypan

Mocho		Brown gravelly, sandy, or 	Qht, Qhty, Qhl, Qhly,
		clay loam, deposited by  	Qhf, Qhfy Qhff
		major creeks

Orestimba	Grayish brown clay loam to 	Qhff, Qhf
		silty clay loam with 
		calcareous, mottled subsoil; 
		some areas affected by alkali

Pescadero	Dark grayish brown clay with 	Qhff, Qhf
		mottled, calcareous subsoil; 
		some areas affected by alkali

Pleasanton	Brown gravelly loam to clay 	Qpf
		loam with compact subsoil

Positas-	Brown to reddish-brown acid 	Qoa
Saratoga	loam to gravelly loam with 
		claypan subsoil

San Ysidro	Brown loam to clay loam with 	Qpf
		claypan subsoil, on same 
		terraces with Pleasanton soils

Sorrento	Brown gravelly, sandy, or 	Qhf, Qht, Qhl
		silty loam to clay loam, 
		recently deposited by creeks

Sunnyvale	Black clay to clay loam with 	Qhff, Qhb
		strongly calcareous, mottled 
		subsoil

Tidal marsh	Land periodically covered by 	Qhbm
		the tide

Yolo		Brown gravelly or sandy loam 	Qht, Qhty, Qhl, Qhly, Qhf, Qhfy
		to clay loam recently 
		deposited by creeks

Zamora		Brown gravelly clay loam, 	Qhf, Qht, Qhl
		silty clay loam, or clay loam 
		with slightly compact subsoil



2. Eastern Santa Clara area 

Soil survey reference: Lindsey, W. D., and Weisel, C. J., 1974, Soil survey of 
the eastern Santa Clara area, California,  U. S. Department of Agriculture, Soil
Conservation Service, 90 p., 49 map sheets at 1:24,000 scale.

Quadrangles covered, or partially covered: Calaveras Reservoir, Mt. Day, Eylar 
Mountain, Mt. Boardman, Lick Observatory,  Isabel Valley,  Mt. Stakes, Morgan 
Hill, Mt. Sizer, Mississippi Creek, Mustang Peak,  Mt. Madonna, Gilroy, Gilroy 
Hot Springs, Pacheco Peak, Pacheco Pass,  Watsonville East, Chittendon, San 
Felipe, Three Sisters

Soil Series	Soil Classification		Typical Quaternary unit(s)
Arbuckle	Typic Haploxeralf		Qhf, Qf
Azule 		Mollic Haploxeralf		Qoa, Qof
Campbell	Aquic Xerorthent		Qhf, Qhff
Clear Lake	Typic Pelloxerert		Qhf, Qhff
Cortina		Typic Xerofluvent		Qhf, Qhl, Qht, Qhty
Cropley		Chromic Pelloxerert		Qhf
Esparto		Typic Haploxeralf		Qhf, Qf
Garretson	Typic Xerorthent		Qht, Qhty, Qhl, Qhf
Hillgate	Typic Palexeralf		Qpf, Qpa, Qoa
Keefers		Mollic Haploxeralf		Qpf
Los Robles	Mollic Haploxeralf		Qpf, Qf
Maxwell		Typic Pelloxerert		Qhf, Qf
Pacheco		Aquic Haploxeroll		Qhf, Qhff
Pleasanton	Mollic Haploxeralf		Qpf, Qf
Rincon		Mollic Haploxeralf		Qpf, Qf, Qhf
San Ysidro	Typic Palexeralf		Qpf
Sunnyvale	Typic Calciaquoll		Qhf, Qhff
Willows		Typic Pelloxerert		Qhf, Qhff
Yolo		Typic Xerorthent		Qhf, Qht, Qhl, Qhfy, Qhly, Qhty
Zamora		Mollic Haploxeralf		Qhf, Qht, Qhl


3. Alameda area 

Soil survey reference: Welch, L. E., Huff, R. C., Dierking, R. A., Cook, T. D., 
Bates, L. A., and Andrews, W. F., 1966, Soil survey of the Alameda area, 
California,  U. S. Department of Agriculture, Soil Conservation Service, Series 
1961, No. 41, 95 p., 42 map sheets at 1:20,000 scale 

Quadrangles covered, or partially covered: Oakland East, Las Trampas Ridge, 
Tassajara, Byron Hot Springs, Bethany, Hayward, Dublin, Livermore, Altamont, 
Midway, Niles, La Costa Valley, Mendenhall Springs, Cedar Mountain, Milpitas

Soil Series	Soil Description		Typical Quaternary unit(s)
Azule 		Grayish-brown clay loam with 	Qoa, Qof
		dark grayish-brown clay subsoil

Clear Lake	Dark gray clay with calcareous 	Qhf, Qhff, Qhb
		silty clay subsoil

Danville	Grayish-brown silty clay loam	Qhf

Livermore	Brown, gravelly, sandy loam	Qht, Qhty, Qhf, Qhfy

Pescadero	Gray clay, alkaline		Qhb, Qhff

Pleasanton	Grayish-brown gravelly loam 	Qpf, Qf
		with brown gravelly clay loam 
		subsoil

Positas		Brown gravelly loam with 	Qoa
		reddish-brown clay subsoil

Rincon		Grayish-brown clay loam with 	Qpf, Qf, Qhf
		brown clay subsoil

San Ysidro	Pale brown  massive loam with 	Qpf
		hard, brown clay subsoil

Solano		Pale brown fine sandy loam, 	Qhf, Qhff, Qhb
		saline-alkaline

Sunnyvale	Gray clay loam with strongly 	Qhf, Qhff, Qhb
		calcareous silty clay subsoil 
		with mottles

Sycamore	Light brownish-gray silt loam	Qhf, Qhff

Yolo		Loam to sandy or gravelly 	Qhf, Qht, Qhl, Qhfy, Qhly, Qhty
		loam

Zamora		Grayish brown silty clay loam 	Qhf, Qht, Qhl
		with clay loam subsoil



4. Western Alameda County 

Soil survey reference: Welch, L. E., 1981, Soil survey of Alameda County, 
California, western part: U. S. Department of Agriculture, Soil Conservation 
Service, 103 p., 8 map sheets at 1:24,000 scale

Quadrangles covered, or partially covered: Oakland West, Oakland East, San 
Leandro, Hayward, Newark, Niles, Milpitas

Soil Series	Soil Classification		Typical Quaternary unit(s)
Azule 		Mollic Haploxeralf		Qoa, Qof
Botella		Pachic Argixeroll		Qhf , Qhff
Clear Lake	Typic Pelloxerert		Qhf, Qhff
Danville	Pachic Argixeroll		Qhf
Lagenour	Aeric Fluvaquent		Qhf
Marvin		Aquic Haploxeralf		Qhf, Qhff
Pescadero	Aquic Natrixeralf		Qhb, Qhf
Pleasanton	Mollic Haploxeralf		Qpf, Qf
Reyes		Sulfic Haplaquept		Qhbm
Rincon		Mollic Haploxeralf		Qf, Qhf, Qpf
Sycamore	Aeric Haplaquept		Qhf, Qhfy
Tierra		Mollic Palexeralf		Qoa
Willows		Typic Pelloxerert		Qhf, Qhff, Qhb
Yolo		Typic Xerorthent		Qhf, Qhl, Qht, Qhfy, Qhly, Qhty
 

5. Contra Costa County 

Soil survey reference: Welch, L. E., 1977, Soil survey of Contra Costa County, 
California,  U. S. Department of Agriculture, Soil Conservation Service, 
National Cooperative Soil Survey, 122 p.,  54 map sheets at 1:24,000 scale.

Quadrangles covered, or partially covered: Mare Island, Benecia, Port Chicago, 
Honker Bay, Antioch North, Jersey Island, Bouldin Island, San Quentin, Richmond, 
Briones Valley, Walnut Creek, Clayton, Antioch south, Brentwood, Woodward 
Island, Oakland East, Las Trampas Ridge, Diablo, Tassajara, Byron Hot Springs, 
Bethany, Dublin

Soil Series	Soil Classification		Typical Quaternary unit(s)
Antioch 	Typic Natrixeralf		Qpf, Qf
Botella		Pachic Argixeroll		Qhf
Brentwood	Typic Xerochrept		Qhf, Qha
Capay		Typic Chromoxerert		Qf, Qhf, Qhff
Clear Lake	Typic Pelloxerert		Qhf, Qhff, Qhb, Qf
Conejo		Pachic Haploxeroll		Qhf
Cropley		Chromic Pelloxerert		Qha, Qhf, Qa
Delhi		Typic Xeropsamment		Qps, Qhs
Garretson	Typic Xerorthent		Qht, Qhty, Qha, Qhay, Qhf, Qhfy
Lagenour	Aeric Fluvaquent		Qht, Qhty, Qha, Qhay, Qhf, Qhfy
Los Robles	Typic Xerochrept		Qhf
Merritt		Fluvaquentic Haploxeroll	Qha
Omni		Fluvaquentic Haplaquoll		Qhf, Qhff 
Pescadero	Aquic Natrixeralf		Qhff, Qhb
Positas		Mollic Palexeralf		Qoa
Rincon		Mollic Haploxeralf		Qpf, Qf, Qhf
Sacramento	Vertic Haplaquoll		Qhfb
San Ysidro	Typic Palexeralf		Qpf
Solano		Typic Natrixeralf		Qhf, Qhff, Qhb
Sorrento	Calcic Haploxeroll		Qhf 
Sycamore	Aeric Haplaquept		Qhf , Qhff, Qhfb
Zamora		Mollic Haploxeralf		Qhf, Qht, Qhl, Qf
 

6. Solano County 

Soil survey reference: Bates, Leland A., 1977, Soil survey of Solano County, 
California: United States Department of Agriculture, Soil Conservation Service, 
112 p., 54 map sheets at 1:24,000 scale.

Quadrangles covered, or partially covered: Mount Vaca, Allendale, Dixon, Saxon, 
Mount George, Fairfield North, Elmira, Dozier, Liberty Island, Cordelia, 
Fairfield South, Denverton, Birds Landing, Rio Vista, Mare Island, Benicia, Port 
Chicago, Honker Bay, Antioch North, Jersey Island

Soil Series	Soil Classification		Typical Quaternary unit(s)
Alviso		Typic fluvaquent		Qhb, Qhdm, Qhbm
Antioch 	Typic Natrixeralf		Qpf, Qf
Brentwood	Typic Xerochrept		Qhf, Qha, Qhay
Capay		Typic Chromoxerert		Qhf, Qhff
Clear Lake	Typic Pelloxerert		Qhf, Qhff
Columbia	Aquic xerofluvent		Qht, Qhty, Qhay, Qhfp
Conejo		Pachic Haploxeroll		Qhf
Corning		Typic Palexeralf		Qoa
Egbert		Fluvaquentic Haplaquoll		Qhff
Joice		Typic Medisaprist		Qhbm, Qhdm
Omni		Fluvaquentic Haplaquoll		Qhff, Qhf
Pescadero	Aquic Natrixeralf		Qhff
Reiff		Typic Xerofluvent		Qhf
Reyes		Sulfic Haplaquepts		Qhdm, Qhbm
Rincon		Mollic Haploxeralf		Qpf, Qf, Qhf
Ryde		Cumulic Haplaquoll		Qhdm
Sacramento	Vertic Haplaquoll		Qhff, Qhfb
San Ysidro	Typic Palexeralf		Qpf, Qpb
Solano		Typic Natrixeralf		Qhf, Qhff, Qpf
Sycamore	Aeric Haplaquept		Qhf, Qhfy
Willows		Typic Pelloxerert		Qhf, Qhff
Yolo		Typic Xerochrept		Qhf, Qhfy, Qhl, Qhly, Qht, 
						Qhty, Qha, Qhay
 

7. Sonoma County 

Soil survey reference: Miller, V. C., 1972, Soil Survey of Sonoma County, 
California: United States Department of Agriculture, Soil Conservation Service, 
188 p., 123 map sheets at 1:20,000 scale.

Quadrangles covered, or partially covered: Gualala, Ornbaum Valley SW, McGuire 
Ridge, Gube Mountain, Big Foot Mountain, Asti, The Geysers, Whispering Pines, 
Stewarts Point, Annapolis, Tombs Creek, Skaggs Springs, Geyserville, Jimtown, 
Mount St. Helena, Plantation, Fort Ross, Cazadero, Guerneville, Healdsburg, Mark 
West Springs, Calistoga, Arched Rock, Duncan Mills, Camp Meeker, Sebastopol, 
Santa Rosa, Kenwood, Rutherford, Bodega Head, Valley Ford, Two Rock, Cotati, 
Glen Ellen, Sonoma, Point Reyes SE, Petaluma, Petaluma River, Sears Point, 
Petaluma Point

Soil Series	Soil Classification		Typical Quaternary unit(s)
Arbuckle	Mollic Haploxeralf		Qf, Qpf
Baywood		Pachic Haploxeroll		Qds, Qmt
Blucher		Typic Haplaquoll		Qhf, Qha, Qhb
Clear Lake	Typic Pelloxerert		Qhf, Qhff, Qhb
Cole		Pachic Argixeroll		Qhf, Qha, Qht
Cortina		Typic Xerofluvent		Qhf, Qhfy, Qht, Qhty, Qhc
Haire		Abruptic Palexeroll		Qoa
Huichica	Abruptic, Haplic Durixeralf	Qoa
Los Robles	Mollic Haploxeralf		Qf, Qpf
Pajaro		Typic Haplaquoll		Qhf, Qha, Qhb
Pleasanton	Mollic Haploxeralf		Qpf, Qpa, Qf
Positas		Mollic Palexeralf		Qoa, Qof, Qot, Qpa, Qpf, Qpt
Reyes		Fluventic Haplaquept		Qhbm
Rohnerville	Typic Tropohumult		Qmt
Wright		Typic Albaqualf			Qoa, Qb
Yolo		Typic Xerorthent		Qhf, Qhfy, Qht, Qhty, 
						Qha, Qhay, Qhl, Qhly
Zamora		Mollic Haploxeralf		Qf, Qt, Qa, Qhf, Qha, Qht
 


8. Napa County 

Soil survey reference: Lambert, G., and Kashiwagi, J., 1978, Soil Survey of Napa
County, California: United States Department of Agriculture, Soil Conservation 
Service, 104 p., 47 map sheets at 1:24,000 scale.

Quadrangles covered, or partially covered: Jericho Valley, Knoxville, Detert 
Reservoir, Aetna springs, Walter Springs, Brooks, Calistoga, St. Helena, Chiles 
Valley, Lake Berryessa, Kenwood, Rutherford, Yountville, Capell Valley, Sonoma, 
Napa, Mt. George, Fairfield North, Cuttings Wharf, Cordelia

Soil Series	Soil Classification		Typical Quaternary unit(s)
Bale		Cumulic Ultic Haploxeroll	Qhf, Qha, Qht
Clear Lake	Typic Pelloxerert		Qhf, Qhff, Qhb
Cole		Pachic Argixeroll		Qha, Qhf, Qht
Coombs		Ultic Haploxeralf		Qoa, Qof, Qpa, Qpf
Cortina		Typic Xerofluvent		Qhf, Qhfy, Qht, Qhty, Qhc
Egbert		Cumulic Haplaquoll		Qhff, Qhf
Haire		Typic Haploxerult		Qoa
Maxwell		Typic Pelloxerert		Qhff, Qhf, Qf
Perkins		Mollic Haploxeralf		Qf, Qhf
Pleasanton	Mollic Haploxeralf		Qpf, Qpa, Qf
Reyes		Fluventic Haplaquept		Qhbm
Yolo		Typic Xerorthent		Qhf, Qhfy, Qht, Qhty, 
						Qha, Qhay, Qhl, Qhly
Zamora		Mollic Haploxeralf		Qf, Qt, Qa, Qhf, Qha, Qht


9. Marin County 

Soil survey reference: Kashiwagi, James H., 1985, Soil Survey of Marin County, 
California: United States Department of Agriculture, Soil Conservation Service, 
229 p., 13 map sheets at 1:24,000 scale.

Quadrangles covered, or partially covered: Valley Ford, Two Rock, Tomales, Point
Reyes NE, Petaluma, Petaluma River, Drakes Bay, Inverness, San Geronimo, Novato,
Double Point, Bolinas, San Rafael, San Quentin, Point Bonita, San Francisco 
North

Soil Series	Soil Classification		Typical Quaternary unit(s)
Ballard		Typic Argixeroll		Qhf, Qht
Blucher		Fluvaquentic Haploxeroll	Qhf, Qha, Qhay, Qhfy
Clear Lake	Typic Pelloxerert		Qhb, Qhf
Cole		Pachic Argixeroll		Qhf, Qha, Qhay, Qhfy
Cortina		Typic Xerofluvent		Qhf, Qhfy
Fluvents, 	Fluvent 			Qhc, Qhay
channeled
Olompali	Ultic Palexeralf		Qmt
Reyes		Sulfic Fluvaquent		Qhbm
Rodeo		Aquic Paleustoll		Qa
Sirdrak		Ustic Dystropept		Qds


10. Western San Mateo County 

Soil survey reference: Wagner, R. J. and Nelson, R. E., 1961, Soil Survey of San
Mateo Area, California: United States Department of Agriculture, Soil 
Conservation Service, Series 1954, no. 13, 112 p., 49 map sheets at 1:15,840 
scale.

Quadrangles covered, or partially covered: Montara Mountain, Half Moon Bay, 
Woodside, San Gregorio, La Honda, Mindego Hill, Pigeon Point, Franklin Point, 
Big Basin, Ano Nuevo

Soil Series	Soil Description		Typical Quaternary unit(s)
Baywood		Gray sandy loam formed from 	Qmt, Qds
		eolian sand blown from beaches

Botella		Very dark gray loam over 	Qha, Qht, Qhf, Qa, Qt, Qf
		dark grayish brown clay loam 
		with subangular blocky structure

Corralitos	Grayish brown sandy loam over 	Qhf, Qht, Qha, Qhfy, Qhty, Qhay
		stratified sand or loamy sand 
		(entisol)

Denison		Dark-colored clay loam on 	Qht, Qhf, Qha
		granitic alluvium (mollisol 
		to vertisol)

Dublin		Dark-colored clay on 		Qhf, Qha, Qht
		sedimentary alluvium

Elkhorn		Dark gray sandy loam over 	Qmt
		brown medium acid sandy clay 
		loam with blocky structure

Farallone	Dark-gray loamy coarse sand 	Qhf, Qha, Qht
		to loam (mollisol)


Lockwood	Gray loam over grayish brown 	Qf, Qa, Qt	
		slightly acid clay loam, on 
		alluvium derived from siliceous 
		shale

Soquel		Dark-colored loam over 		Qha, Qht, Qhf
		stratified alluvial sediments 
		derived from sedimentary rocks 
		and older soils

Tunitas		Dark-colored loam to clay loam 	Qf, Qa, Qt, Qha, Qht, Qhf
		on alluvium derived from 
		sedimentary and basic igneous 
		rocks

Watsonville	Dark gray acid loam with a 	Qmt
		light gray leached horizon over 
		a yellow-brown clay pan subsoil



11. Eastern San Mateo County and San Francisco County

Soil survey reference: Kashiwagi, J. H., and Hokholt, L. A., 1991, Soil Survey 
of San Mateo County, eastern part, and San Francisco County, California: United 
States Department of Agriculture, Soil Conservation Service, 120 p., 12 map 
sheets at 1:24,000 scale.

Quadrangles covered, or partially covered: San Mateo, Mountain View, Woodside, 
Mindego Hill, La Honda, Montara Mountain, Redwood Point, Hunters Point, San 
Francisco South, Oakland West, San Francisco North

Soil Series	Soil Description		Typical Quaternary unit(s)
Botella		Pachic Argixeroll		Qha, Qht, Qhf, Qa, Qt, 
						Qf, Qpf, Qpa
Francisquito	Typic Haploxeralf		Qpf, Qpa, Qoa, br
Novato		Typic Hydraquent		Qhbm
Reyes		Sulfic Fluvaquent		Qhbm
Sirdrak		Ustic Dystropept		Qds
Typic 		Typic Argiustoll		Qmt
Argiustoll




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



                         Open-File Report 00-444
                          Appendix C of Part 3
                               Version 1.0

 


                                APPENDIX C

              A PRELIMINARY DIGITAL COMPENDIUM OF GROUND EFFECTS 
                      ASSOCIATED WITH EARTHQUAKES 
                    IN THE SAN FRANCISCO BAY REGION



                               prepared by

             Perry Wong(2), Kent Aue(2), Keith L. Knudsen(2), 
             Carl M. Wentworth(3), and Robert S. Nicholson(3)


                             from the work of

           Youd and Hoose, 1978, and Tinsley and others, 1998






                           Author Affiliations

                  2 - California Division of Mines and Geology
                  3 - U.S. Geological Survey





This report is preliminary and has not been reviewed for conformity with U.S. 
Geological Survey editorial standards or with the North American Stratigraphic 
Code. Any use of trade, product, or firm names is for descriptive purposes only 
and does not imply endorsement by the U.S. Government.



                                INTRODUCTION

Ground effects such as sand boils, lateral spreads, and landslides have been 
associated with numerous damaging earthquakes in the San Francisco Bay region, 
particularly the 1906 San Francisco and 1989 Loma Prieta earthquakes.  Knowledge
of the location and character of past ground failures provides a guide to their 
future occurrence, particularly through association with the various Quaternary 
map units in the region.  Past effects have been mapped and compiled for 
northern California by Tinsley and others (1998) for the 1989 Loma Prieta 
earthquake and by Youd and Hoose (1978) for previous historic earthquakes.

We have assembled this information in a digital database for the nine-county San
Francisco Bay region as points, lines, and polygons (areas) with associated 
attributes, working from the published 1:100,000- and 1:24,000-scale maps of 
Tinsley and others (1998) and from 1:24,000-scale relocations of the historic 
data catalogued by Youd and Hoose (1978).  The locations, station numbers, and 
summary of effects are shown on map sheet 2, Liquefaction Susceptibility, and 
are included in the database.  Original station numbers from the two source 
documents are recorded in the database and shown on the map to facilitate 
recovery of complete descriptions for each station.

Youd and Hoose (1978) include landslides in their compilation and refer to the 
earthquake effects in aggregate as "ground failures", whereas Tinsley and others
(1998) exclude landslides and refer in aggregate to "ground effects".  We follow
our sources by including catalogued historic landslides that were caused by 
earthquakes prior to 1989 but not Loma Prieta landslides, and refer in aggregate
to ground effects, recognizing that many are ground failures and presuming that 
all but the landslides are probably related to earthquake-triggered 
liquefaction.  No distinction is made here between ground failures due to 
liquefaction and those caused by deformation of soft clay. More complete 
information about earthquake-related landslides in the region can be obtained 
from Keefer, 1998, and references cited therein.

There are inherent difficulties in converting locations and descriptions from 
the source documents into precise digital spatial data because of uncertainties 
in the location, the areal extent around points and along and across mapped 
lines, and the limits to mapped areas.  This is particularly true for the 
historic dataset. The database as a whole has a scale resolution no better than 
1:100,000, although some map elements are more accurately located, particularly 
the San Francisco localities digitized at 1:24,000.  The accuracy of location 
for each digital element is categorized by individual mapped occurrence in the 
database.  These uncertainties in location require that the digital data not be 
used blindly, especially in precise GIS operations, and that the resolution of 
the data be respected. 

Design of the database, digital encoding of the Loma Prieta data, and 
preparation of the final aggregate database and its graphic representation are 
the responsibility of Wentworth and Nicholson; relocation, interpretation, and 
digital encoding of the historic data are the responsibility of Wong, Aue, and 
Knudsen.


                        HISTORIC GROUND EFFECTS

Youd and Hoose (1978) catalogued and interpreted descriptions of observed ground
effects in northern California for several major earthquakes and the great 1906 
San Francisco earthquake from many sources, including newspaper articles and 
earlier technical reports.  Within the nine-county region, the ground failures 
catalogued by Youd and Hoose (1978) occurred during the period 1838 through 
1969.  Sites of the catalogued effects were numbered and located on topographic 
maps using symbols representing the different types of effects.  The maps are at
a scale of 1:250,000 except for localities within the City of San Francisco, 
which are shown at 1:24,000.  Accuracy of location was rated in three categories
(table 1), and descriptions from the original compilation sources were quoted.


Table 1. Location-Accuracy Categories of Youd and Hoose (1978).

  A	"a site that can be accurately relocated"
  B	"a site that can be relocated to within a few kilometers and probably 
	could be located more accurately with further investigation"
  C	"a site where the information is insufficient to allow precise location"


                             Relocation

Many of the historic sites of Youd and Hoose (1978) can be placed more 
accurately at 1:24,000 than is shown on the 1:250,000 maps through comparison of
the quoted descriptions in their tables 6, 7, and 8 with more detailed 
topographic maps.  In relocating sites by reference to cultural features, the 
earliest available 1:62,500- and 1:24,000-scale maps are used, because some 
bridges and roads have been moved during the past century and some cultural 
features identified in the descriptions are shown only on earlier maps or are 
renamed on more recent maps.  Modern 1:24,000 contours are used where location 
was described in terms of topography and where the location of landslides can be
estimated from their topographic expression. 

A few localities that experienced liquefaction were placed by the descriptions 
in areas of exposed bedrock.  Where possible, these localities are moved onto 
nearby surficial deposits using recent geologic maps.  The extent of ground 
failure was described numerically for a few locations, and this information is 
recorded in the extent field (EXT) of the database.

The accuracy of each relocation is separately rated according to the categories 
of table 2.  These accuracies are specific to the individual relocated map 
elements (points, lines, areas), whereas the Youd and Hoose accuracies refer to 
their numbered localities, which can include several ground effects that are 
distinguishable at 1:24,000. 


Table 2. Relative Accuracy of Relocated Historic Effects

  P	located to within 100 meters
  Q 	located to within 500 meters
  R 	located to within 1 kilometer
  S	location is indefinite or approximate


                        Digital Representation

Relocated occurrences of the historic ground effects are represented by points, 
lines, and polygons that have been digitized at a scale of 1:24,000.  Station 
numbers are those of Youd and Hoose, and therefore are not unique identifiers of
the relocated occurrences where more than one mapped occurrence has been 
extracted from one Youd and Hoose locality. 

Accuracy ratings are reported as presented by Youd and Hoose (table 1), and 
where different table entries for the same locality were given different 
ratings, these are aggregated for the locality (for example, 'B,C') and are 
assigned to each of the relocated occurrences for that locality.  Accuracy 
ratings for the relocated occurrences (table 2) are separately assigned.  The 
resulting accuracy ratings for each map element in the ACC database field thus 
have two parts, a Youd-and-Hoose rating followed by a relocation rating, the two
separated by a colon (for example 'A:P').

Points are used to record the location of small features that cannot be shown as
polygons at 1:24,000 and for occurrences that cannot be accurately located, 
including areas that are only generally identified or have unspecified 
dimensions, such as landslides. 

Lines are used to record linear features or a continuous or intermittent series 
of occurrences described along a linear feature such as a stream or road or 
along a linear trend.  Locations are approximate along the lines and width of 
occurrence is generally unspecified.  The locations of the ends of the lines are
generally only approximate.

Polygons are used to record areas having identifiable boundaries and a size 
sufficient to show at 1:24,000.  Where boundaries cannot be delineated with 
reasonable confidence, a point is used.  Typically, the polygon areas represent 
the distribution of discontinuous effects, such as scattered sand boils.  


                        LOMA PRIETA GROUND EFFECTS

Tinsley and others (1998) present the map location of liquefaction and 
associated effects triggered by the 1989 Loma Prieta earthquake for much of the 
region at a scale of 1:100,000 and for San Francisco at 1:24,000, and provide 
tabular descriptions of the mapped occurrences.  The occurrences range from 
Richmond Harbor and Bolinas Lagoon south to the Salinas Valley, but only those 
within the nine-county San Francisco Bay region are included here.  In contrast 
to the historic dataset, the Loma Prieta effects were carefully mapped soon 
after the earthquake, making relocation from the descriptions unnecessary 
(except for some lines, see Digital Representation below). 

Many of the map locations were presented by Tinsley and others (1998) as 
numbered station points with associated effect symbols, but other point 
locations lack the station point and have less certain locations.  Some station 
points are accompanied by arrows designating the extent of the effect (for 
example, along  a road or stream), although none of these occur within the 
nine-county region.  Areas of sand boils are shown by regular patterns of dots, 
the boundaries of most of which seem to have been carefully delimited.  Some of 
these patterned areas are irregular in shape, others involve two parallel lines 
of dots along a linear feature such as a highway.  One other area of indistinct 
perimeter is shown by a group of five different effect symbols (station 50). 
 

                         Digital Representation

The locations of the occurrences are represented as points, lines, and polygons 
that have been digitized from the published 1:100,000- and 1:24,000-scale maps. 
These maps provide the most accurate source available for the dataset (Tinsley, 
oral commun., 2000).  Station numbers are as assigned by Tinsley and others 
(1998).  Accuracy ratings are assigned according to the relocation categories of
table 2, based on the kind of map representation presented by Tinsley and 
others.  Stations with location points, all lines, and well delineated areas are
rated P, whereas stations without location points and the indistinctly defined 
area (station 50) are rated Q. 

Most stations are represented by points in the database, including localities 
without location points.  All areas on the source maps are shown as polygons in 
the database, except for several patterned areas that seem from the descriptions
to represent extents along roads or other linear features; these are represented
in the database as lines drawn along those linear features on the published 
maps.


                                REFERENCES CITED

Keefer, D.K., ed., 1998, The Loma Prieta, California, earthquake of October 17, 
  1989-landslides: U.S. Geological Survey Professional Paper 1551-C.

Tinsley, J.C. III, Egan, J.A., Kayen, R.E., Bennett, M.J., Kropp, Alan, and 
  Holzer, T.L., 1998, Appendix: maps and descriptions of liquefaction and 
  associated effects, in Holzer, T.L., ed, The Loma Prieta, California, 
  Earthquake of October 17, 1989-liquefaction: U.S. Geological Survey 
  Professional Paper 1551-B, p. B287-B314, map scales 1:100,000 and 1:24,000.

Youd, T.L., and Hoose, S.N., 1978, Historic ground failures in northern 
  California triggered by earthquakes: U.S. Geological Survey Professional Paper
  993, map scales 1:250,000 and 1:24,000.