269, Construct a horse riding ring, Studies & ReportsC M
ENGINEERING GEOLOGIST
• URBAN GEOLOGY
• SEISMICITY
• GRADING CODE CONSULTANT
3094 ROUNDUP CIRCLE • THOUSAND OAKS, CALIFORNIA 91360 • (805) 492-8127 / 492-8027
April 22, 1982
Project #82111
Mr. Bill Stromberg.
2413 Hill `Lane
Redondo Beach, CA 90278
C. Michael Scullin
Engineering Geological Evaluation
Lot 1, Tract 22932
#8,Buggy Whip Drive
Rolling Hills, CA'90274
INTRODUCTION
In accordance with your request, an engineering geologic study and
evaluation ofthe subject property has been conducted to determine
geologic'safety"and feasibility of development of a• horse stable,
riding ring and corrals. An areal geologic site location map has
been included with this report. The map is a reproduction of a
portion of>CDMG Map Sheet 27,' "Geology' of the Northeast'Part of
the. Palos Verdes .Hills, L.A. County, 1976 by George.B. Cleveland.
This investigation was based upon:
Geologic field reconnaissance and detailed mapping conducted
April 21, 1982 in conjunction with review of records at the
County of Los Angeles Geology Section and the records in the
offices of Pacific Soils Engineering, Inc. of Harbor City, CA.
r-
I,'
n
. Review of the following reports by Pacific Soils Engineering,
Inc.; .
r‘i .
(1) Preliminary Soil and Geologic Investigation Report,
. „
, ...k,
WO #5838, July 6 1965.
(2) Addendum reports: Sept. 1, 1972; Oct. 23, 1972 and
Dec. 20, 1972, Sept. 22, 1975. .
(3) Final Compaction Report, WO #200597 Nov. 7, 1975 and
Page,2
April 22, 1982
Project #82111
2.4 Review of pertinent reports and geologic maps of the adjacent
'14rs
areas prepared by this office and others.
Final Geology Report, Nov. 7, 1975.
4. L.A. County Geology Review Sheet by Mr. Robert E. Smith,
March 26, 1982.
5. A topography map and as -graded plan at a scale of 1/16" = 11.
and a 2' contour interval,'10/14/81, by F.J. Saimen & Assoc.
Civil Engineers, Redondo Beach, California.
ACCOMPANYING ILLUSTRATIONS
Area Geologic Lqcation Map
(CDMG Special Rpt. 27, 1976) Page 5
Site Geologic Map
Appendix'
. .
'
171
4Y'
PRINCIPALS
Owner: •
Civil. Engineer:.
Original Geotechnical
Engineers:
Engineering
Geologist
PROPOSED,DEVELOPMENT
Number of Lots:
Type of Development:
Adjoining .the. Site:.
Previous Use of Site:
Existing Condition of Site:
Sewage Disposal:
Access to Development:
Page 3
April 22, 1982
Project:#82111
Mr. Gerry Webber
#2 Buggy Whip Drive
Rolling Hills, CA 90274
Phone: (213) 377-0226
F.J. Salmen .& Associates
1924 S. ' Pacif is Coast Hwy,
Suite "E"
Redondo Beach, CA 90277
Phone: (213) 316-0829
Pacific Soils Engineering, Inc.
1402 240th Street
Harbor City, CA
Phone: (213) 775-6771
C. Michael Scullin, EG170
3094 Roundup Circle
Thousand Oaks, CA 91360
Phone: (805) 492-8127
492-8027
• One lot
Residence, horse stable, riding
ring and 3 to 4 corrals.
N'ly Residence
S'ly - Residence
E'ly - Buggy Whip Drive
W'ly - Residence and range
Residence and range
Residence, stable, riding ring
and corrals.
Seepage pits
N'ly of Crest Road on Buggy
Whip Drive, E'ly of Crenshaw
7,77,4
PHYSIOGRAPHIC SETTING
Geomorphic Province:
Landform:
Page 4
April 22, 1982
Project 182111
Peninsular Ranges
Upper portion of a lateral
canyon
Topographic Relief: Highest: 1110'±
Lowest: 1050'±
Maximum Relief of Site:
Average Natural Slope:
Average Proposed Cut Slope:
Maximum Th,ickness of Fill:
Thickness 3f Topsoil:
Thickness of Colluvial Soils:
Drainage:
Rainfall:
Climate:
60'±
2:1 to 10:1
Retained vertical or 2:1
1' to 8'±
2' to 3'±
3',to 7'±
NW'ly to the ravine and thence
NE'ly
12 inches mean annual during
32 year base period: 1932-1964
Mediterranean
Vegetation: Mustard, rye grasses, sage,
evergreen and landscaping
Inf iltrat ion : .
Erosion Hazard:
Low
Low except where water is
concentrated
fr
't o.w
• v' 3°22'30"
1_3
CARTOGRAPHY DRAFTED BY
VIVIAN'W. HUSTON
Mae Sh1-;2.1
.-P1cef0 1, /176
„0
•
t1
age -lb
r.5:,.`:2 q,...1
c ' '#8
98-2 1�
Page 6
April 22, 1982
Project 1182111
ENGINEERING GEOLOGY
GENERAL SETTING
The subject, site is located on a north and west facing ravine head
of a lateral canyon that drains NW'ly into a north-northeast trending
canyon. The site drainage is northerly to the ravine and thence
northwesterly toward the canyon. The site is within a northeasterly
. trending ridgetop of the Palos Verdes Hills, situated within Rolling
Hills, California.
The subject site has been developed as a single family residence.
The site was initially cut and filled as part of a grading permit
that was geotechnically.inspected, tested and approved by Pacific
Soils Engineering, Inc.,'WO 11200597, their final approval of
grading and retaining walls Nov. 7, 1975. This report from this
office covers the grading for the horse stable, riding circle and
corrals.
EARTH MATERIALS
The subject site is underlain by artificial fill (Af), thick adobe
soils (ts), Colluvium (Col), and the Altamira Member (Tma) of the
Monterey Formation. of Middle to Upper Miocene Age.
ARTIFICIAL FILL (Af)
The surface of the site contains 1' to 8'± of engineer compacted
artificial fill throughout most of the building site area. This
r-"
Page 7
April 22, 1982
Project #82111
fL11 was approved by Pacific Soils Engineering Inc. (see geologic
map!). The slope below the stable and the riding ring is composed
of fill containing clay and clayey sand matrix with shale cobbles
and angular fragments. The till matrix is dark brown, medium
brown and black, moist and has caving characteristics. The fill
for theriding ring was compacted but not engineered nor tested.
TOPSOIL (ts) and COLLUVIUM (Col)
Topsoil, two to three feet thick is located throughout the site '
and colluvium up to 7' thick underlies the natural slope areas
:Y. of the site. The soils are black clayey silt or silty clay. It
r .
is generally moist, firm, soft and contains angular cobble size
fragments of the bedrock. The engineering parameters of the
topsoil and colluvium are provided by the soil engineer in the
.Pacific Soil Engineering reports. It appears to be moist, com-
pressible, plastic and has expansiveTotential. The slope areas
exposing this soil are located in the corral area.
BEDROCK (Tma)
The site is underlain by the Altamira.Member of the Monterey
Formation. The bedrock on this site contains siltstone and shale,
•gray and rust brown, thin bedded, moist and firm. Interbeds of
siliceous, tuffaceous and diatomaceous shale; gray, rust to buff
brown, and white colored; moist, and very firm to tight with some
black chert. Some of the siliceous interbeds are extremely hard
and blocky. Some minor fine grained sandstone interbeds are
• s," 1: • :
• • • '
"7 '7 .r."..;" r ," 77" '777" 777. •
Page 8
April 22, 1982
Project #82111
occasionally.found. The diatomaceous shale and very hard siliceous
:and porcelaneous shale appear to be the predominate bedrock beneath;
this site. It is vertically jointed, blocky and breaks along
joints into flat slabs.
GEOLOGIC STRUCTURE
.The Cabrillo Fault is located approximately a mile
and the Palos Verdes Fault is approximately 4 miles
the site.. The property is involved within a southwesterly dipping
block.. The trends are consistently N10-70W and dip southwesterly,
at 12° to'35°.• The bedding planes underlying thestable structure
and cut slope dip favorably into the slope. The area geologic
map by George Cleveland indicates southwesterly, dips of 5° to 16°
adjacent to the site. These correlate with the 15° - 20° dips
.SW'ly mapped by Pacific Soils Engineering, Inc. during their pre-
liminary investigation and grading. Some dip reversals were noted
beneath;the engineered fill below the residence. No shears were
found ih the exploration; however, there is some vertical jointing
within the.shale.interbeds. .No landsliding was found within the
site area. A topsoil slump was noted by Pacific Soils adjacent
to,the riding ring. The lot area appears favorable due to the:,
bedding dipping favorably into the slope, the hard tight resistant
bedrock and the engineered fill, stability fill and engineered
retaining walls in the residence area. However, mudflow potential
within the top soils and colluvium is moderate to high on the
natural slope as is the case throughout the Palos Verdes hills.
the northeas
northeast of
Page 9
April 22, 1982
Project #82111
ree flowing. water or seeps, were found within the site investi-
gation nor duringthe Pacific Soils Engineering . g Inc. investigations.
.No.water table noted within the'data reviewed.of the site area.
Thick grasses were noticeable throughout the adjacent.lot indi-
cating. moisture retention. within the ,adobe 'topsoils
CONCLUSIONS
FEASIBILITY OF DEVELOPMENT
The subject site is considered geologically safe and feasible for
the .proposed residential development, stable, riding ring and
corrals...
FAVORABLE ENGINEERING GEOLOGIC CONDITIONS
.. The underlying: bedrock within the site area contains bedding
planes that dip into the natural terrain and are self-supporting
'are. stabilized by a stability fill and retaining walls.
Groundwater problems are not in evidence nor anticipated.
Liquefaction, ground lurching and differential compaction
hazard potential,is considered lowin the subject building
site areas.
4. Earth materials can be readily excavated with modern earth -
moving. equipment.
Page 10
April 22, 1982
Project #82111
UNFAVORABLE ENGINEERING GEOLOGICAL CONDITIONS
1. Thick (adobe) fills, fill, and slopewash soils mantle the site
and appear to have expansive potential and compressible
characteristics.
. The topsoil and colluvium materials within the rear slope
corral area have a potential for surface mudflow.
GEOLOGIC GUIDELINES AND CONSIDERATIONS
1.„ Expected ground shaking from possible future earthquakes
is sun!narized in Table III and in the following seismic
parameters:
Acceleration
0.27g
Period
Duration
0;30 seconds 19 seconds
The repeatable high ground acceleration used for design pur-
poses would average 65 percent of the (peak) acceleration.
Low to moderate strong ground motion is anticipated at the,
site during the lifetime of the structures and buildings
should be designed to withstand itaccording to the building
code criteria for seismic design.
2. The roof drainage and yard drainage should be conducted in,
improved devices to drain southerly and westerlyinto the
rubble ravine and thence down the ravine into the riding ring
desilting basin. The concrete culverts and the riding ring
will: act as a desilting
properties.
Page 11.
April 22, 1982
Project #82111
basin that will protect the adjacent
We suggest that the (3)`exiting 4" pipes (Section B-B' on :the
site plan) be extended toward .the desilting basin .with- a
T-joint and perforated stand pipes be constructed in caseof
basin siltation.
The easterly portion of the riding ring should be regraded to
tilt ,back toward the toe of landscaped slope with a swale•
draining southerly into a pipe inlet to drain onto the rubble
rip -rap in the basin. Likewise, the access road from the
stable to the riding circle should be graded to drain to the
existing drain swale southerly of the riding circle and thence
down., toward the outlet of the concrete culvert.
The outlet of the concrete culvert should be filled with rock
rip -rap similar to the desilting basin inlet. The culvert-
splashpad and velocity reducers do not have a curtain wall
to.reduce the undermining due to headward erosion. Conse-
.quently,'th•e rip -rap is considered necessary.
The desalting basin slopes and th•e rear slope areas should be
planted with fire, retardant and water resistant plants or
forage grasses for the horses. The less landscape watering
of the rear slope, the longer it will perform without mudflow.
Studies have indicated that the
average hillside homeowner in
the L.A. Basin area uses the equivalent of 75" to 120" of
Page 12
April 22, 1982
Project #82111
rainfall per year per lot in their normal landscape water
application. With the annual rainfall added to these totals,
the local mediterranean climate is changed to a rain forest
condition. Such abuse to natural or engineered slopes results
in mudflows. Limited watering in the summer and no watering
during rainy seasons will generally satisfy water resistant
plants.
7. The mudflow slump mapped by Pacific Soils Engineering, Inc.
has been partially removed. and partially covered by fill in.
the riding ring area and is not,considered anymore of a
,`potential hazard than any .of the natural slope area.
The stable, riding ring and corral areas are considered geo-
logically safe as long as the drainage provisions suggested
above are constructed along with the existing drainage control
already existing and slopes are landscaped or planted. We
'feel that the horse development is safe for its intended use
an'dUshould not be a hazard to adjacent properties. The riding
ring area will act as a desilting basin and will provide a
better flood control capability than if left in the natural
state. It should provide much more safety against flood hazard
potential than before.
•
9. The riding ring-desilting basin slopes are composed of com-
pacted fill. However, it was not an engineered compacted fill
and consequently is considered as a non-structural fill. Any
7777
r7
Page 13
April 22, 1982
Project #82111
subsequent conversion to a structural use would require the
removal, keying and recompaction under the supervision of a
soil engineer. The fill was compacted satisfactorily for the
existing purposes intended.
FINAL CONCLUSION
•The subject site is considered geologically favorable for the
horse stable, riding ring and corrals providing that the slope
planting and the above guidelines are considered in site design
and construction. This office assumes no responsibility for the
footing and stable construction nor the residential development
done under inspection by others.
The geological services that I rendered in this investigation were
.performed to the best of my ability, utilizing my best professional
,and ethical judgment at the time the work was performed.
Conclu-
sions and recommendations presented in this report are'professional
opinions, .based upon current available data and do not constitute
.a warranty.
We appreciate being of service to you. If you have any questions,
please do not •hesitate to call.
Respectfully submitted,
C. MICHAEL SCULLIN
Engineering Geologist, EG170
cc: (6) Bill Stromberg
(1) File
PACIFIC SOILS ENGINEERING, INC.
1402 W. 240TH STREET, HARBOR CITY, CALIFORNIA 90710
TELEPHONES: (213) 325.7272 OR 775-6771
Mr. Kirk Gillette
1506 Crenshaw Blvd.
Torrance, California. 90501
Final Geologic Report. for.
Lot- 1 , Tract No. 22932;
08'Buggywhip Drive
City of Rolling Hills, California
ORANGE COUNTY OFFICE
17921 Sky Park Circle (Suite G)
Irvine, Ca. 92707
(714) 557.9450
VENTURA COUNTY OFFICE
1429 Thousand Oaks Brvd. (Suite 208)
Thousand Oaks, Ca. 91360
(805) 495.6513
(805) 495.6514
November 7, 1975
Work Order 200597
Reference: Final Soils Engineering Report on above subject property
dated November 7, 1975 by Pacific Soils Engineering, Inc.
(Work Order 200597).
Dear Sir:
This transmittal, prepared in conformance with the grading codes of the City of
Rolling Hills, presents this firm's geologic opinions relative to recent grading on
the subject property. Recommendations of a geologic nature made prior to and
during grading have been incorporated into construction. That is, unsuitable soils
were removed prior to compacted fill placement and an equipment width stabilization
fill was placed along the north margin of the site. •
From the foregoing it is the opinion of this office that the lot is geologically acceptable
'for residential construction. •
Attached hereto is a grading plan displaying pertinent geologic data.. This map was also
utilized for preparation of the referenced soils report which is a companion to this report.
b
Respectfully submitted,
PACIFIC SOILS. ENGINEERING, INC.
MI HAEL F. MIL '•
Engineering Geologist Associate
Distr.: (6) addressee
MFM:SSN/andi
Reviewed by:
.IDNEY
.E.G.
ETT, Vicq/President '•.
40
Geol
Soils Engineer
Site Address Ba% 5
Location %zj `o,/l� n All
Developer/Owner Mr v . rVei. / S PY"
GEOLOGIC REVIEW'SHEET
COUNTY OF LOS ANGELES
DEPARTMENT OF COUNTY ENGINEER - FACILITIES
ENVIRONMENTAL DEVELOPMENT DIVISION
ENGINEERING GEOLOGY SECTION
738-2161.
f"w'/i�� . ,Dr /Ye.. Lod / 7 ,9v7 'f
Engineer • t% / ! i n oh A 5 S 'e t•
ogist P� c 1 !i l e Sao• i I 01. (v4 serer^I).
PAC/ C t C Sol I- rep rr r r
J .
PLAN CHECK NO. OR DATE OF REPORT(S)
Review of: • •
es Grading Plan No. ;1-.0 /
❑ Building Plan No
❑ Geologic Report Dated
❑ Soils Report Dated
❑ Other
0 Plan is approved
❑ Plan approved subject to conditions below
54
J ❑
s Ium h 4.s Lee'n r1ielppe d
•ir.-the aver ' 1 ibetrorose.cl
gqIre cl jn . I I't eo Aoc I S 1 arc. ,oj I. a racj in ar
0old rna ke ao oienc/a-Iior+s on 41,7e 12 a 5- s
S ir.PA
fhe
a e GlVel:0 et.'f
SHEET / OF
DISTRIBUTION:
7 ❑
Plan Check
Dist. Engineer
Developer -Owner
Site Engineer
Geologist
Soils Engineer
Geol. Sect. File
Grading Section •
Plan is not approved for reasons below
J Submit plans for recheck
Reviewed by
Sec. 309 Code requirements
met (not met)
Sec. 308(b) 3c & e code requirements
rnet (not met)
. Sin: ¢tt
/.
/1ia44 26, (f�'z
`•r