Andrew C. (Andrew Cowper) Lawson.

Geologic atlas of the United States : San Francisco folio online

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Online LibraryAndrew C. (Andrew Cowper) LawsonGeologic atlas of the United States : San Francisco folio → online text (page 1 of 16)
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San Francisco Folio










Geography 9

Situation and general divisions of the area 9

Area east of San Francisco Bay 10

Relief 10

Drainage 11

Soil 13

Vegetation 14

Climate 15

San Francisco Peninsula 16

Relief and drainage 16

Shore lines 18

Soil 18

Vegetation 19

Climate 20

Marin Peninsula 20

Relief 30

San Andreas rift valley 22

Point Reyes Peninsula 22

Soil 23

Vegetation 23

Climate 24

Bay of San Francisco 25

Geology 28

Stratigraphy and areal geology 38

Geologic formations of the middle Coast Ranges 28

Pre-Franciscan rocks 31

Character and distribution .. 31

Gavilan limestone 31

Quartz diorite ("Montara granite") 31

Jurassic (?) rocks 34

Franciscan group and associated igneous rocks 34

Character 34

Stratigraphy 34

Cahil, Marin, and Bonita sandstones 35

Character 35

Calera limestone member of Cahil sandstone 38

Sausalito and Ingleside cherts . 40

General character 40

Petrographic features 41

Fossils 43

ij Distribution and tiiickness 44


(ieology — Continued. Page.
Stratigraphy and areal geology — Continued.
JuraBsic (?) rocks — Continued.

Franciscan group and associated igneous rocks — Continued.

Conditions of sedimentation 44

Contemporaneous volcanic rocks 46

Intrusive rocks associated with the Franciscan group. 47

Peridotite and serpentine 47

tSilica-carbonate rock 50

Spheroidal basalt and diabase 50

Metaniorphic rocks 52

Age of the Franciscan group 54

Cretaceous system 57

Distribution 57

Lower Cretaceous (Shasta) series 58

Knoxville formation 58

Upper Cretaceous series 60

Chico foriuation 60

Oakland conglomerate member 60

Upper part of Chico formation 62

Fossils 63

Tertiary system 64

Eocene series 64

Subdivisions 64

Martinez formation 65

Character and distribution 65

Fossils 66

Rocks of San Pedro Point 67

Tejon formation 68

Distribution and character 68

Fossils 69

Miocene series 70

Monterey group 70

Petrographic character 70

Relations to older formations 73

Subdivisions 75

Sobrante sandstone 78

Fossils of lower faunal zone 78

Claiemont shale 79

Oursan sandstone 80

Tice shale . ^ 80

Hambre sandstone ,._. 81

Rodeo shale 81

Fossils of juiddle faunal zone 81

liriones sandstone 82

( 'haracter and distribution 82

Hercules shale member 82

Fossils of upper faunal zone ^^3

Partly differentiated Monterey strata in the Con-
cord quadrangle 83

Undifferentiated Monterey sti-ata in the Tamalpais -^

q uad ran gle 84

Hasalt . __. 85

Geology — Continued. Page.
Stratigraphy and areal geology — Continued.
Tertiary system — Continued.
Miocene series — Continued.

San Pablo formation 86

(jreneral features 86

Distribution 86

Thickness 87

Age 87

Fossils 88

Pliocene series 89

Leona rhyolite __. 89

Distribution and chax'acter 89

Chemical composition .. 91

Field relations 92

Age 92

Northbrae rhyolite 93

Distribution __. 93

Correlation 93

Petrographic features 93

Pinole tuff 94

General features 94

Peti'ogi-aphic character 95

Distribution 96

Orinda formation 97

General features 97

S*tratigraphic relations 98

Fossils 99

Age 100

Merced formation 101

General character and distribution .__ 101

Stratigraphic relations 101

Fossils L 103

Berkeley group ^ 104

General description 104

Moraga formation ^ 105

Siesta formation 106

Bald Peak basalt . 106

Relations of the group to adjacent formations 106

Tertiary and Quaternary deposits 107

Santa Clara formation 107

Quaternary system 108

Pleistocene series 108

Campus formation 108

Alameda formation , 109

San Antonio formation . Ill

Merritt sand 112

Terrace gravel . 113

Recent series ; 113

Temeseal formation . 113

Other recent deposits 114

Terrace deposits 114

Travertine 114


Geology — Continued. Page.
Stratigraphy and areal geology— Continued.
Quaternary system — Continued.
Recent series — Continued.

Other recent deposits — Continued.

Dunes 114

Salt-marsh deposits 114

Structure 115

General features 115

Montara block 116

Faults 116

Folds : 118

San Francisco-Marin block -._ 131

Faults 121

Folds 123

Berkeley Hills block 125

Faults 125

Folds 133

(ieologic history 138

Pre-Franciscan time 138

Franciscan epoch 139

Knoxville epoch 140

Chico epoch 141

Martinez epoch 142

Tejon epoch 143

Monterey epoch _. 143

San Pablo epoch A 145

Merced epoch 146

Berkeley epoch 147

Deformation at close of Tertiary period 147

Campus epoch ■. 148

Alameda epoch 148

Post- Alameda diastrophism 148

San Antonio epoch 149

Merritt and Temescal epoch 149

Recent uplift and depression 150

Changes in drainage 152

Economic geology 154

Available resources 154

Water . 154

Brick clays _ 159

Orinda formation 159

Siesta formation . 160

Alluvial and marsh clay 160

Shale for making bricks and cement IGI

Limestone 161

Crushed rock 162

Gravel and sand. . 163

Abrasive 164

Greensand _ 164

Oil 164

Salt... __. 165

Pyritc 165


Economic geology — Continued. Page.

Quicksilver 166

Mangane'e 16T

Lead 169

Gold 169

Copper I'i^"

Asbestos, chroniite, talc, and niagnesite ITO

Minerals IW

Earthquakes and construction 171

Literature l^-")


Maps, etc. (in pocket):
Topographic maps.

Colnnmiar section (on back of Tamalpais topographic map).
Areal-geology maps.
Structure-section sheets.
Plates (at end of text) :

I. Steeply tilted rocks of Ban Pedro Point, San Mateo quadrangle.
II. Western front of the Berkeley Hills, viewed from the north across
the canyon of Strawberry Creek.

III. Calera limestone member of Cahil sandstone, Franciscan group,

Calera Point, San Mateo quadrangle.

IV. San Francisco Bay, from the Berkeley Hills.

V. Ellipsoidal structure in intrusive basalt, Hunter Point, San

VI. Ellipsoidal basalt intrusive into thin-bedded radioiarian chert of
Franciscan group, Hunter Point, San Francisco.
VII. Thin-bedded chert and shale of the Claremont formation,
Monterey group, Clai-emont Canyon, Berkeley Hills.
VIII. Minutely folded thin-bedded radiolarian chert of Franciscan
group exposed in quarry in Golden Gate Park, San Francisco.
IX. San Andreas rift valley; view southeastward toward Crystal

Springs Lake, San Mateo quadrangle.
X. Trace of San Andreas fault, made by the movement which
caused the earthquake of 1906.
Figures: • Page.

1. Index map of central California 10

2. Map of vicinity of San Francisco Bay, showing topographic

features and the geomorphic divisions resulting from the
adjustment by tilting of great fault blocks 10

3. Outline map of the Tamalpais, San Francisco, Concord, San

Mateo, and Haywards quadrangles, showing the limits of

the great fault l)locks, the larger faults, and the axes of folds 11")

4. Outline map of the western slope of the Berkeley Hills in the

southwestern jjart of the Concord quadrangle and adjacent
parts of the San Francisco and Haywards quadrangles,
showing the deflection of streams by the longitudinal rift
valley of the Haywards fault zone 127



By Andrew C. Lawson."



The five sheets of the San Francisco folio — the Tama 1 pais,
Ban Francisco, Concord, San Mateo, and Haywards sheets —
map a territory lying between latitude 37° 30' and 38° and
longitude 122° and 122° 45'. Large parts of four of these
sheets cover the waters of the Bay of San Francisco or of the
adjacent Pacific Ocean. (See fig. 1.) Within the area mapped
are the cities of San Francisco, Oakland, Berkeley, Alameda,
San Rafael, and San Mateo, and many smaller tOAvns and vil-
lages. These cities, which have a population aggregating about
750,000, together form the largest and most important center
of commercial and industrial activity on the west coast of the
United States. The natural advantages afforded by a great
harbor, where the railways from the east meet the ships from all
ports of the world, have determined the site of a flourishing-
cosmopolitan, connnercial city on the shores of San Francisco
Bay. The bay is encircled by hilly and mountainous country
diversified by fertile valley lands and divides the territory
mapped into two rather contrasted parts, the western part being
again divided by the Golden Gate. It will be convenient to
sketch the geographic features under four headings — (1) the area
east of San Francisco Bay; (2) the San Francisco Peninsula;
(3) the Marin Peninsula; (4) San Francisco Bay. Figure 2
shows the topography of this general region.

" Seo note on page i^.



Montcj-e y{^



Figure 1. — Index map of central California.

The location of the five quadrauKles described in the San Francisco folio is shown by the darker
ruling (No. 193). Published folios describing other quadrangles are indicated by lighter
ruling and the proper serial numbers and are included in the numerical list on tlie back cover
of this folio.


Relief. — The area east of San Francisco Bay embraces a belt
of billy country lying between the bay and the western flank
of Mount Diablo. The ridges trend generally northwest and
southeast. Portions of two wide valleys lie within this area.
One of these is the valley of San Francisco Bay, on whose
shores stand the cities of Berkeley, Oakland, and Alameda; the
other is Ygnacio Valley, which occupies the northeast corner
of the Concord quadrangle and extends with a very flat slope
northward beyond the limits of the quadrangle to the shores of
Suisun Bay. The southern extension of this valley, up the
dniinago line of Wnlnut Creek, is the well-defined flat-bottomed


Figure 2. —Ma

The eastern boundi
of the Berkeley
The submerged
land was siibme


Figure 2. —Map of vicinity of San Francisco Bay, showing topographic features and the geomorphic divisions resulting
from the adjustment by tilting of great fault blocks.

The eastern boundary of the Berkeley Hills block is not sharply deflced; it may be drawn along a general zone of overthrust folding and faulting just e«st
of the Berkeley HUls. on which the Mount Diablo thrust block has ridden westward. This thrust movement antedated the tilting of blocks to the west
The submerged bar outside the Golden Gat« originated as a delta deposit of the stream that flowed in the old valley of San Francisco Bay before tJiir

The five quadrangles described in this folio are shown by heavier lines than the b

s of other i|uadranglei



San Kanion Valley, which sharply separates tlie belt of hills
above mentioned from Mount Dial)lo, the greater mass of
which lies farther east, in the adjacent quadrangle. The domi-
nant range of hills is that which forms the southwestern limit
of the belt and which immediately overlooks the Bay of San
Francisco. The culminating point on this range is Bald Peak,
east of Berkeley, which stands at an altitude of 1930 feet above
sea level. Otiier peaks whose altitudes afford an idea of the
general height of the range are Grizzly Peak, 1759 feet;
Round Top, 1750 feet; and Redwood Peak, 1608 feet. This
range is commonly referred to as the Berkeley Hills, although
the area to which that term is applicable appears to be rather
vaguely defined. It is also often referred to as the Contra
Costa Hills, but this term apparently applies more properly
to the broad group of hills between the Bay of San Francisco
and Mount Diablo. A rather well defined line of valleys,
including San Pablo and Moraga valleys, separates this
dominant range from the more eastern portion of the hilly
belt. The hills thus lying between the dominant ridge and
Ygnacio and Ramon valleys show a less pronounced linear
trend, are much more mature in their geographic expression,
and in general are much lower. The culminating points in
this part of the belt are Rocky Ridge (2000 feet) on the south,
and the Briones Hills (1432 feet) on the north.

In the Haywards quadrangle there is a notable sag in the
longitudinal profile of the range, and at Haywards there is a
gap at the level of the alluvial plain, which here stands about
100 feet above sea level. This gap is the outlet of a remark-
ably open low valley known as Castro Valley.

Drainage. — The drainage of the area includes several features
worthy of special mention :

1. The dominant ridge of the hill belt does not form the
divide that separates the waters flowing directly to the Bay of
San Francisco from those flowing to Suisun Bay by way of
Walnut Creek, in San Ramon and Ygnacio valleys. The
divide runs through tlie center of the belt of hills, so that a
very considerable portion of the lower ground northeast of the
dominant ridge is drained either through or around the end of


the ridge. The soiitliern half of the range drains through
gaps in the ridge, which form outlets to the bay for San Lean-
dro and San I^orenzo creeks. Tlie northern half is drained
by San Pablo Creek, which flows around the end of the main
ridge, and by Pinole Creek, which flows to San Pablo Bay.

2. A second feature of the drainage of especial interest is
that, though the streams on the northeast side of the dominant
ridge are manifestly subsequent, those draining the southwest-
ern slope of the same ridge directly to the bay are as mani-
festly consequent, presenting a condition which suggests that
the slope to San Francisco Bay is of more recent origin
than the maturely dissected hill country farther northeast — a
suggestion which is more fully discussed in this text, under
the heading "Structure."

3. A third feature is the prevailing alluviation of the valley
bottoms and the steep-sided stream trenches cut in the alluvium,
which do not as a rule reach the bedrock, clearly indicating
that the former conditions in this area favored more vigorous
downward corrasion by the streams, at a time when the can-
yons and valleys were deeper, and that with the passing of
these conditions others ensued which reduced the transporting
power of the streams and caused them to drop their load of
detritus in the bottoms of the canyons and valleys, making
these flat and broad, as well as helping to give the country its
geomorphically mature aspect and adding to its agricultural
value. Since these flat-bottomed valleys were thus formed
there seems to have been a slight but distinct tendency toward
a recurrence of tlie older conditions, indicated by the trench-
ing of the valley floors, but this trenching may be due, in part
at least, to the disturbance of natural conditions caused by

Attention may be called also to the rather noteworthy con-
vergence of drainage in Castro Valley near Haywards. Most
of this drainage is carried l)v San Lorenzo Creek throuR'h a
pronounced ))i'eak in the Berkeley Hills.

The only other notable feature of the drainage is the fact
tliat the stream flowing in San Bamon Valley, the largest,
most mature, and broadest valley in the Concord quadrangle,


has cut tliroii.i;li tlie alluvium on the vallev floor at several
places, particuhn-ly from Alamo to the village of Walnut
Creek, where it runs on bedrock.

Soil. — The soils of the country may be divided into two
classes. The soil on the hillsides and ridge tops above the
level of the valley floors is sedentary — that is to say, it has
been formed in place by the chemical and mechanical disinte-
gration of the underlying rocks. This soil has l)een modified
chiefly by tlie abstraction of certain constituents which nour-
ished the generations of plants that have grown upon the sur-
face and by the addition of organic matter formed by the decay
of the same vegetation. On these hill slopes earthworms ai-e
uncommon, probably because the soil is very dry and parched
during the summer, so they have not aided in turning over and
mixing the soil and in thus making it more useful for agricul-
ture. This work, however, lias been performed, probably
with equal efficiency, by several kinds of burrowing mammals,
such as the gopher (Thomomys) and the ground squirrel (Sper-
mophilus). These animals formerly infested the region in
great numbers and have persisted there until very recently,
in spite of the eff'orts of the farmers to destroy them, but
during the last few years, by more systematic efforts, the
health authorities have almost completely exterminated them,
because they are regarded as a menace to the public health as
propagators of the bubonic plague through the fleas wdiich infest

These sedentary soils, having been formed from the immedi-
ately underlying rocks, vary in character from place to place,
and here and there the slopes are so steep that little or no soil
can accuniulate. The soils derived from the Cretaceous and
Eocene formations are perhaps those best adapted to agricul-
ture, but they lie chiefly on high ground that is cut by rather
steep canyons, so that they are not so generally cultivated as
the soils of the lower ground. The sandstones of the Monte-
rey group, which are very quartzose, yield nearly everywhere a
light sandy soil, whereas the shale and chert formations of the
same group yield scant and poor soils. Considerable areas
that are underlain by the shale and chert carry no soil what-


ever, the bare mechanically disintegrated rock forming the sur-
face of the ground. The fresh-water deposits of the Orinda
formation have generally yielded deep and excellent soils,
which, however, are in man}^ places heavy and clayey.

The soil in the bottoms of the vallej'^s is not sedentary but
has been derived from various sources in the course of the
degradation of the surrounding hills and is excellent. It varies
from a sandy to a clayey loam and in certain localities is even
gravelly, but in practically all places it is well adapted to suc-
cessful tillage.

Vegetation. — The region is almost devoid of forest. Hill-
tops and slopes are bare of trees (see PI. II) and the prevail-
ing mantle of vegetation in uncultivated tracts is composed
of the wild oat {Aveiia fatua) and other wild grasses {Danthonia
californica, Festuca myuros, Lolium temulentum, and species
of Hardeum); but on the south sides of steep canyons the
slopes may be covered with a more or less dense growth of
brush. The only native timber to which the term forest
might be applied is the grove of redwoods (Sequoia semper-
virens) on the west side of Redwood Canyon, extending from
the creek to the summit of Redwood Peak. The only other
conifers in the district are the digger pine {Pinus sabiniana),
which is a feature of the lower slopes of Mount Diablo on
the east side of San Ramon Valley, and the knobcone pine
(Pinus alter iiata), which grows locally on the summit of the
first ridge east of Redwood Canyon.

The most abundant tree is the live oak (Quercus agrifolia),
common in canyons and on north and east slopes and also
notable for filling shallow gulches or south and west slopes of
otherwise treeless hills. The valley oak (Quercus lobata) is
characteristic of the open valleys, growing onl}'^ sparingl}'^ or
not at all on the hills. It is most common in San Ramon and
Ygnacio valleys. The blue oak (Quercus douglasii) is scattered
over dry hills in the eastern part of the area. The buckeye
(JEsculus californica) grows along the bases of low hills. The
laurel (Umbellularia californica) is the commonest tree in can-
yon bottoms. It also clusters about rocky knolls on ridges and
slopes. Along the stream courses are found the red alder


[Alnus oregona) and the white alder (Alnus rhomb if olia), the
latter, however, only east of the crest of the Berkeley Hills.
There are three willows, the most abundant and widely distrib-
uted being the white willow or arroyo willow (Salix lasiolepis),
which thrives in dry gulches in the hills as well as along living
streams. The yellow willow (Salix lasiayidra) and the red wil-
low [Salix Iwvigata) are mostly confined to living streams. The
madrone [ArhiLtun menziesii) is rare and is found chiefly with the
redwoods but extends northward to Strawberry Canyon. The
big-leaf maple {Acer macrophyllum), the box elder {Negundo
caUformcwu), and the sycamore {Platanus racemosa) are rare.
The California walnut [Juglans californica) grows along
streams at Walnut Creek and Lafayette. Taking the territory
as a whole, the brush-covered areas are more striking than the
wooded areas. The brush of the Berkeley Hills is composed
chiefly of nine-bark [Neillia capitata), cofl*ee berry [Rhamnus
californica), hill scrub [Baccharis pilularis), poison oak (Bhus
diversiloba), and mountain lilac {Ceanothus thyrsiflorus and
C. sorediatus). Typical chaparral is not common, although
colonies of manzanita {Arctostaphylos manzanita) and similar
shrubs are found, particularly east of the crest of the Berkeley
Hills. Chamiso grows more or less extensively on Las Tranipas
Ridge, on the hill east of Bed wood Peak, and at the base of
Mount Diablo."

Climate. — The crest of the Berkeley Hills is a dividing line
for the climate of this region. The climate of the area east of
the crest is somewhat like that of the interior valleys; that
of the west slope of the Berkeley Hills is like that of the coast.
In the area east of the crest the summers are hotter and the
winters are colder than in the area farther west. The sea
breezes and fogs that temper the summer heat on the west
slope have a greatly diminished influence on the east side of
the Berkeley Hills. The annual rainfall at Berkeley is about
27.48 inches, and it falls almost wholly in winter, the summer
being rainless. Snow rarely falls, even on the highest ground,
and no snowfall lasts more than a day.

"Furiijucli of the information contained in thiss and otiier paragraphs
dealing with the vegetation the writer is indebted to Prof. W. L. Jepson.



The territory west of the Bay of San Francisco is naturally
divided into a northern and a southern part by the Golden
Gate. South of the Golden Gate lies the San Francisco Penin-
sula, with the city of San Francisco at its northern extremity;
north of it lies the Marin Peninsula, w^hose most notable fea-
ture is Mount Tamalpais.

Relief and drainage. — The San Francisco Peninsula is divided
into two parts by Merced Valley. Each of these parts has the

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Online LibraryAndrew C. (Andrew Cowper) LawsonGeologic atlas of the United States : San Francisco folio → online text (page 1 of 16)