a division of Utah Geological Survey Special Study 133 ...€¦ · ZION NATIONAL PARK...
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Lund, Tyler R. Knudsen, and David L. Sharrow Plate 7 Utah Geological Survey Special Study 133 Zion National Park Geologic-Hazard Study Area, Washington and Kane Counties, Utah Camp Creek Creek Horse Ranch Mountain Taylor Fork North Fork Middle Fork South Lee Pass Nagunt Mesa Buck Pasture Mountain Creek Timber Kolob Canyons Road Shuntavi Butte Gregory Butte Kolob Arch Langston Mountain Creek La Verkin Willis Creek BEAR CANYON TRAP KOLOB CANYONS Burnt Mountain HOP VALLEY Firepit Knoll Pine Valley Peak Northgate Peaks North Guardian Angel South Guardian Angel Kolob Terrace Road Kolob Terrace Road North Creek Right Fork Left Fork Blue Creek Goose Creek Lava Point Kolob Creek Deep Creek Coalpits Wash Wash Scoggins Altar of Sacrifice The West Temple Meridian Tower The Sentinel Mount Kinesava Wash Huber Creek Oak The Watchman Johnson Mountain FORK EAST RIVER VIRGIN PARUNUWEAP CANYON Bridge Mountain The East Temple Mount Spry Crater Hill Twin Brothers Mountain of the Sun The Great Arch The Great White Throne Lady Mountain Castle Dome Mount Angels Landing Observation Point Mountain of Mystery Wynopits Mountain Ivins Mountain Timber HURRICANE CLIFFS Death Point Tucupit Point Paria Point Beatty Point Top Mountain Herbs Point LANGSTON CANYON Currant Creek Cane Creek POLE CANYON LOWER KOLOB PLATEAU UPPER KOLOB PLATEAU HORSE PASTURE PLATEAU ZION CANYON OR D E R V I LLE CANY O N The Subway GREAT WEST CANYON COUGAR MOUNTAIN Court Patriarchs The of Creek Birch Creek Pine Creek Pine Creek Clear Checkerboard Mesa Creek Clear Creek Co-op GIFFORD CANYON FORK NORTH RIVER VIRGIN ZION-MOUNT CARMEL T U N N E L TUNNEL Wash Terry Wash Jennings Wash Coalpits The Bishopric HEAPS CANYON ECHO CANYON Cable Mountain Temple of Sinawava TELEPHONE CANYON IMLAY CANYON BULLOCH GULCH THE NARROWS FORK NORTH RIVER VIRGIN WILDCAT CANYON RUSSELL GULCH North Creek North Creek Zion Canyon Scenic Drive 9 9 The Grotto Zion Canyon Visitor Center Zion Lodge Little Creek Grapevine Wash TOWERS VIRGIN THE OF Abraham Isaac Jacob Church Mesa PHANTOM VALLEY CORRAL HOLLOW Kolob Creek Weeping Rock Cathedral Mountain Majestic Kolob Canyons Visitor Center WASHINGTON CO KANE CO IRON CO WASHINGTON CO Neagle Ridge Bullpen Mountain Pocket Mesa OAK SPRING VALLEY PINE VALLEY LEE VALLEY Cave Knoll CAVE VALLEY Tabernacle Dome Wash Spring Pine TRAIL CANYON Greatheart Mesa BEHUNIN CANYON Creek Shunes Shunesburg Mountain Wash Hepworth Wash Dennett Canyon Bee Hive Peak HIDDEN CANYON CANYON MYSTERY R 12 W R 11 W T 38 S T 39 S R 11 W R 10 W T 40 S T 41 S T 41 S T 42 S T 39 S T 40 S T 41 S T 42 S T 39 S T 40 S T 40 S T 40.5 S T 41 S T 42 S R 11 W R 10 W R 10 W R 12 W R 11 W R 10 W R 9.5 W R 9.5 W R 9 W 37 27' 30" 37 25' 37 22' 30" 37 20' 37 17' 30" 37 15' 37 12' 30" 37 10' 37 10' 37 12' 30" 37 15' 37 17' 30" 37 20' 37 22' 30" 37 22' 30" 37 25' 113 5' 113 2' 30" 113 37 22' 30" 112 57' 30" 112 55' 112 52' 30" 112 52' 30" 112 55' 112 57' 30" 113 113 2' 30" 113 5' 113 7' 30" 113 10' 113 12' 30" 113 12' 30" Zion National Park Geologic-Hazard Study Area boundary Zion National Park boundary County boundary State highway Minor road Foot trail Existing park structure Area not studied 37 27' 30" MAP LIMITATIONS This map is based on limited geologic and geotechnical data; site-specific investigations are required to produce more detailed geotechnical information. The map also depends on the quality of those data, which may vary throughout the study area. The mapped boundaries between hazard categories are approximate and subject to change as new information becomes available. The hazard from expansive soil and rock may be different than shown at any particular site because of variations in the physical properties of geologic deposits within a map unit, gradational and approximate map-unit boundaries, and the small map scale. The map is not intended for use at scales other than the published scale, and is designed for use in general planning and design to indicate the need for site-specific investigations. This map shows the location of known or suspected expansive soil and rock in the Zion National Park Geologic- Hazard Study Area. The map is intended for general planning and design purposes to indicate where expansive soil and rock may exist and special investigations should be required. Site-specific investigations can resolve uncertainties inherent in generalized mapping and help identify the need for special foundation designs, site grading and soil placement, or mitigation techniques. The presence and severity of expansive soil and rock, along with other geologic hazards should be addressed in these investigations. If expansive soil or rock is present at a site, appropriate design and construction recommendations should be provided. HAZARD REDUCTION Although potentially costly when not recognized and properly accommodated in project design and construction, problems associated with expansive soil and rock rarely are life threatening. As with most geologic hazards, early recognition and avoidance are the most effective ways to mitigate potential problems. However, expansive soil and rock are present in some of the most heavily developed parts of the study area, and avoidance may not always be a viable or cost-effective option. In Utah, soil-test requirements are specified in chapter 18 (Soils and Foundations) of the 2009 IBC (International Code Council, 2009a) and chapter 4 (Foundations) of the 2009 IRC (International Code Council, 2009b), which are adopted statewide. IBC Section 1803.3 and IRC Section R401.4 contain requirements for soil investigations in areas where expansive soil may be present. Where the presence of expansive soil or rock is confirmed, possible mitigation techniques include soil removal and replacement with noncohesive, compacted backfill; use of special foundation designs such as drilled pier deep foundations, grade beam foundations, or stiffened slab- on-grade construction; moisture barriers; chemical stabilization of expansive clays; and careful site landscape and drainage design to keep moisture away from buildings and expansive soils (Nelson and Miller, 1992; Keller and Blodgett, 2006). Expansive soil and rock increase in volume (swell) as they get wet, and decrease in volume (shrink) as they dry out. Expansive soil and rock contain a significant percentage of clay minerals that can absorb water directly into their crystal structure when wetted. Some sodium-montmorillonite clay can swell as much as 2000 percent upon wetting (Costa and Baker, 1981). The resulting expansion forces can be greater than 20,000 pounds per square foot (Shelton and Prouty, 1979), and can easily exceed the loads imposed by most structures, resulting in cracked foundations and pavement, structural damage, and other building distress. Several bedrock formations in the Zion National Park Geologic-Hazard Study Area consist in whole or part of shale, claystone, or mudstone containing expansive clay minerals. These rock units and the expansive soils derived from them are capable of significant expansion and contraction when wetted and dried, causing structural damage to buildings; cracked roads and driveways; damage to curbs, gutters, and sidewalks; and heaving of roads and canals. Expansive soils are chiefly derived from the weathering of clay-bearing rock formations and may be residual (formed in place) or transported (usually a short distance) and deposited in a new location. The principal transporting mechanisms are water or wind, but soil creep and mass-wasting processes may play important roles locally. For additional information about expansive soil and rock in the Zion National Park Geologic-Hazard Study Area, refer to the Problem Soil and Rock Hazards chapter in this report. UTAH GEOLOGICAL SURVEY a division of Utah Department of Natural Resources in cooperation with National Park Service This geologic-hazard map was funded by the Utah Geological Survey and the U.S. Department of the Interior, National Park Service. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. Although this product represents the work of professional scientists, the Utah Department of Natural Resources, Utah Geological Survey, makes no warranty, expressed or implied, regarding its suitability for a particular use. The Utah Department of Natural Resources, Utah Geological Survey, shall not be liable under any circumstances for any direct, indirect, special, incidental, or consequential damages with respect to claims by users of this product. For use at 1:24,000 scale only. The Utah Geological Survey does not guarantee accuracy or completeness of data. www.geology.utah.gov Base map consists of U.S. Department of Agriculture 2006 National Agricultural Imagery Program natural color aerial photography and shaded relief generated from digital elevation data acquired from the Utah Automated Geographic Reference Center. Universal Transverse Mercator Projection, zone 12 North American Datum of 1983 REFERENCES Chen, F.H., 1988, Foundations on expansive soils: Amsterdam, Elsevier, 463 p. Costa, J.E., and Baker, V.R., 1981, Surficial geology, building with the earth: New York, John Wiley & Sons, 498 International Code Council, 2009a, International building code: Country Club Hills, Illinois, 678 p. International Code Council, 2009b, International residential code for one- and two-family dwellings: Country Club Keller, E.A., and Blodgett, R.H., 2006, Natural hazards – Earth’s processes as hazards, disasters, and Lund, W.R., Knudsen, T.R., Vice, G.S., and Shaw, L, 2008, Geologic hazards and adverse construction Mortensen, V.L., Carley, J.A., Grandall, G.C., Donaldson, K.M., Jr., and Leishman, G.W., 1977, Soil survey of Nelson, J.D., and Miller, D.J., 1992, Expansive soils, problems and practice in foundation and pavement Shelton, D.C., and Prouty, D., 1979, Nature’s building codes: Colorado Geological Survey Special Publication 12, p. Hills, Illinois, 870 p. catastrophes: Upper Saddle River, New Jersey, Pearson Prentice Hall, 395 p. conditions, St. George – Hurricane metropolitan area, Washington County, Utah: Utah Geological Survey Special Study 127, 105 p, 14 plates, digital video disk. Washington County area, Utah: U.S. Department of Agriculture Soil Conservation Service and U.S. Department of the Interior Bureau of Land Management and National Park Service, 139 p., 95 plates, scale 1:24,000. engineering: New York, John Wiley & Sons, 259 p. p. 37-40. Approximate mean declination, 2009 12 9' o TRUE NORTH MAGNETIC NORTH Map Location 1 0 1 0.5 MILE 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET 1 0 1 0.5 KILOMETER SCALE 1:24,000 EXPLANATION EXPANSIVE SOIL EXPANSIVE ROCK CONCEALED HIGHLY EXPANSIVE SOIL OR ROCK High Hazard – Soils classified by the NRCS as having high hazard for volumetric change. These soils are typically clay rich and have a LL >35, PI >15, and/or SCT value of >3 percent swell (Mortensen and others, 1977; Chen, 1988; Nelson and Miller, 1992). Soils having these characteristics are of limited aerial extent in the study area, and are typically associated with the Petrified Forest Member of the Chinle Formation, other clay-rich bedrock units, and some weathered basalt flows. Moderate Hazard – Soils classified by the NRCS as having moderate hazard for volumetric change (LL 25–55, PI 5–35). The LL and PI values in this category overlap at their upper ends with soils in the high hazard category. Chen (1988) recognized that while PI is an indicator of expansive potential, other factors also exert an influence, and therefore reported a range of PI values when categorizing a soil’s capacity to shrink or swell. Low Hazard – Soils classified by the NRCS as having low hazard for volumetric change (LL 0-40, PI from nonplastic to 15). The LL and PI values in this category overlap at their upper ends with soils in the moderate hazard category. However, the low hazard category includes soils with highly variable potential for volumetric change that do not fit easily into the moderate or high categories. No Data – Unconsolidated alluvial deposits in areas of upper Zion Canyon, Hop Valley, and LaVerkin Creek that may contain some clay-rich horizons subject to volumetric change, but a lack of information about the physical characteristics of the deposits precludes hazard categorization. These deposits are not included in the geotechnical database, and are mapped by the NRCS as chiefly Rock Outcrop (NRCS soils-map unit RT) or Fluvaquents and Torrifluvents (NRCS soils-map unit FA) for which soil property estimations and engineering tests were not performed. Due to the variable nature of these deposits and a general lack of geotechnical data for them, we recommend site-specific testing for expansive soil for all proposed construction within map areas having no data. High Hazard – Bedrock units with high shrink/swell hazard, which include claystone horizons in the Virgin Limestone Member of the Moenkopi Formation, the Petrified Forest Member of the Chinle Formation, and the lower red beds of the Dinosaur Canyon Member and the Whitmore Point Member of the Moenave Formation. We include landslides mapped within these rock units in the high-hazard category because the landslides contain debris from high-hazard bedrock units. These bedrock units contain an abundance of expansive clay minerals and are commonly associated with expansive rock problems throughout southwestern Utah. Moderate Hazard – Bedrock units with moderate shrink/swell hazard, which include the Shnabkaib and lower, middle, and upper red members of the Moenkopi Formation; the Sinawava Member of the Temple Cap Formation; and the lower unit of the Co-op Creek Member and the Crystal Creek Member of the Carmel Formation. These rock units are chiefly fine grained and contain alternating strata of shale, claystone, mudstone, siltstone, sandstone, and limestone. Not all or even the majority of these strata contain expansive clay minerals; however, past experience in southwestern Utah has shown that a sufficiently high percentage of strata do contain expansive clay that shrink/swell problems are often associated with these bedrock units. We include landslides mapped within moderate-hazard rock units in this category. Low Hazard – Bedrock units with low shrink/swell hazard, which include the Timpoweap Member of the Moenkopi Formation, the Kayenta Formation, and the Winsor Member of the Carmel Formation. We consider these units to have a lower hazard than the bedrock units identified above; however, low- hazard units contain some fine-grained, clay-rich strata that may cause shrink/swell problems locally. Concealed – Area suspected of having highly expansive soil or rock (>3 percent swell) in the shallow subsurface (<20 feet), with little or no evidence of such material at the ground surface. The likely presence of highly expansive materials in the shallow subsurface is based on the outcrop pattern of the Petrified Forest Member of the Chinle Formation, which indicates that the Petrified Forest Member likely underlies thin unconsolidated deposits in those areas. The Petrified Forest Member typically contains highly expansive shale and claystone, and past experience in southwestern Utah has shown that when wetted, highly expansive soil or rock can cause damaging differential displacements at the ground surface even when overlain by as much as 20 feet of nonexpansive material (Lund and others, 2008). Therefore, we consider areas where the Petrified Forest Member may be present in the shallow subsurface to have a potential for highly expansive soil and rock problems despite the lack of surface evidence of such materials. _ _ _ _ _
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EXPANSIVE-SOIL-AND-ROCK HAZARDSZION NATIONAL PARK GEOLOGIC-HAZARD STUDY AREA
T 38 ST 39 S
37 30'
113 7' 30"
2010
DISCUSSION
USING THIS MAP
SYMBOLS
ByWilliam R. Lund, Tyler R. Knudsen, and David L. Sharrow
Plate 7Utah Geological Survey Special Study 133
Zion National Park Geologic-Hazard Study Area, Washington and Kane Counties, Utah
Camp
Creek
Creek
Horse RanchMountain
Taylor Fork
North
Fork
Middle
Fork
South
LeePass
NaguntMesa
BuckPastureMountain
Creek
Timber
Kolob
CanyonsRoad
ShuntaviButte
GregoryButte
KolobArch Langston
Mountain
Creek
La Verkin
WillisCreek
BEAR CANYONTRAP
KO
LO
B
CA
NY
ON
S
BurntMountain
HO P
VA L L E Y
FirepitKnoll
PineValleyPeak
NorthgatePeaks
NorthGuardian
Angel
SouthGuardianAngel
Kolob
Terrac
eRo
ad
Kolob
Terrace
Road
North
Creek
Right
Fork
Left
Fork
Blue
Creek
Goose
Creek
LavaPoint
Kolob
Creek
DeepCr
eek
Coalp
itsWa
sh
Wash
Scoggins
Altar ofSacrifice
The WestTemple
MeridianTower The
Sentinel
MountKinesava
Wash
Hube
r
Creek
Oak
The Watchman
JohnsonMountain FORK
EAST
RIVER
VIRGIN
P A R U N U W E A P
C A N Y O N
BridgeMountain
The EastTemple
MountSpry
CraterHill
TwinBrothers
Mountainof the Sun
The GreatArch
The GreatWhite Throne
LadyMountain
CastleDome
Mount
AngelsLanding
ObservationPoint
Mountainof Mystery
WynopitsMountain
IvinsMountain
Timber
HU
RR
I CA
NE
CL I
FF
S
Death Point
Tucupit Point
Paria Point
Beatty Point
Top
Mountain
Herbs
Po
intLA
NGST
ON
CANYO
N
Currant
Creek
Cane
Creek
POLE
CANYON
L OW
E R
K OL O
B
P L A T E A U
UP P E R
K OL O
B
P L A T E A U
HO
RS
EP A
ST
UR
E
PL A
TE
AU
ZI O
N
CA
NY
ON
O R D E R V I L L E C A N Y O N
TheSubway
GREAT
WEST
CANYON
COUG
A R MO U N TA I N
CourtPatriarchsTheof
CreekBirch
Creek
Pine
Creek
Pine
Creek
Clear
Chec
kerbo
ard
Mes
a
Creek
Clear Creek
Co-op
GIFFORDCANYON
FORK
NORTH
RIVE
R
VIRGIN
ZION-MOUNT CARMEL TU NN EL
TUNNEL
Wash
Terry Wash
Jennin
gs
Wash
Coalpits
TheBishopric
HEAPS
CANYON
ECHO
CANYON
CableMountain
Temple ofSinawava
TELEPHONE
CANYON
IMLAY
CANYON
BULLOCH
GULC
HT H E
N A R R OWS
FORK
NORT
H
RIVER
VIRGIN
WILDCAT
CANYON
RUSSELLGULCH
North
Creek
North
Creek
Zion
Cany
on
Scen
icDr
ive
9
9
The Grotto
Zion CanyonVisitor Center
ZionLodge
Little
Creek
Grapevine
Wash
TOW
E RS
V I R G I NT H E
O F
Abraham Isaac
Jacob
ChurchMesa
PHANTOM VALLEY
CORRAL
HOLLOW
KolobCreek
WeepingRock
Cathedral Mountain
Majestic
Kolob CanyonsVisitor Center
WASH
INGT
ON C
OKA
NE C
O
IRON COWASHINGTON CO
Neag
le R
idge
BullpenMountain
Pocket Mesa
OAK SPRING VALLEY
PINE
VALLEYLEE
VALLEY
CaveKnoll
CAVE
VALLEY
TabernacleDome
Wash
SpringPine
TRAIL
CANYONGrea
theart
Mesa
BEHUNIN
CANYON
Creek
Shunes
Shunesburg Mountain
Wash
Hepworth
Wash
DennettCanyon
Bee HivePeak
HIDDENCANYON
CANYON
MYSTERY
R 12 W R 11 W
T 38 ST 39 S
R 11 W R 10 W
T 40 ST 41 S
T 41 ST 42 S
T 39 ST 40 S
T 41 ST 42 S
T 39 ST 40 S
T 40 ST 40.5 S
T 41 ST 42 S
R 11 W R 10 W
R 10 W
R 12 W R 11 W
R 10 W R 9.5 W R 9.5 W R 9 W
37 27' 30"
37 25'
37 22' 30"
37 20'
37 17' 30"
37 15'
37 12' 30"
37 10' 37 10'
37 12' 30"
37 15'
37 17' 30"
37 20'
37 22' 30"37 22' 30"
37 25'
113 5'
113 2' 30"
113
37 22' 30"
112 57' 30" 112 55'
112 52' 30"
112 52' 30"
112 55'112 57' 30"
113
113 2' 30"113 5'
113 7' 30"
113 10'
113 12' 30"
113 12' 30"
Zion National Park Geologic-Hazard Study Area boundaryZion National Park boundaryCounty boundaryState highwayMinor roadFoot trailExisting park structureArea not studied
37 27' 30"
MAP LIMITATIONSThis map is based on limited geologic and geotechnical data; site-specific investigations are required to producemore detailed geotechnical information. The map also depends on the quality of those data, which may varythroughout the study area. The mapped boundaries between hazard categories are approximate and subject tochange as new information becomes available. The hazard from expansive soil and rock may be different thanshown at any particular site because of variations in the physical properties of geologic deposits within a mapunit, gradational and approximate map-unit boundaries, and the small map scale. The map is not intended foruse at scales other than the published scale, and is designed for use in general planning and design to indicatethe need for site-specific investigations.
This map shows the location of known or suspected expansive soil and rock in the Zion National Park Geologic-Hazard Study Area. The map is intended for general planning and design purposes to indicate where expansivesoil and rock may exist and special investigations should be required. Site-specific investigations can resolveuncertainties inherent in generalized mapping and help identify the need for special foundation designs, sitegrading and soil placement, or mitigation techniques. The presence and severity of expansive soil and rock,along with other geologic hazards should be addressed in these investigations. If expansive soil or rock ispresent at a site, appropriate design and construction recommendations should be provided.
HAZARD REDUCTIONAlthough potentially costly when not recognized and properly accommodated in project design and construction,problems associated with expansive soil and rock rarely are life threatening. As with most geologic hazards,early recognition and avoidance are the most effective ways to mitigate potential problems. However, expansivesoil and rock are present in some of the most heavily developed parts of the study area, and avoidance may notalways be a viable or cost-effective option.In Utah, soil-test requirements are specified in chapter 18 (Soils and Foundations) of the 2009 IBC (InternationalCode Council, 2009a) and chapter 4 (Foundations) of the 2009 IRC (International Code Council, 2009b), whichare adopted statewide. IBC Section 1803.3 and IRC Section R401.4 contain requirements for soil investigationsin areas where expansive soil may be present. Where the presence of expansive soil or rock is confirmed,possible mitigation techniques include soil removal and replacement with noncohesive, compacted backfill; useof special foundation designs such as drilled pier deep foundations, grade beam foundations, or stiffened slab-on-grade construction; moisture barriers; chemical stabilization of expansive clays; and careful site landscapeand drainage design to keep moisture away from buildings and expansive soils (Nelson and Miller, 1992; Kellerand Blodgett, 2006).
Expansive soil and rock increase in volume (swell) as they get wet, and decrease in volume (shrink) as they dryout. Expansive soil and rock contain a significant percentage of clay minerals that can absorb water directly intotheir crystal structure when wetted. Some sodium-montmorillonite clay can swell as much as 2000 percent uponwetting (Costa and Baker, 1981). The resulting expansion forces can be greater than 20,000 pounds per squarefoot (Shelton and Prouty, 1979), and can easily exceed the loads imposed by most structures, resulting incracked foundations and pavement, structural damage, and other building distress.Several bedrock formations in the Zion National Park Geologic-Hazard Study Area consist in whole or part ofshale, claystone, or mudstone containing expansive clay minerals. These rock units and the expansive soilsderived from them are capable of significant expansion and contraction when wetted and dried, causing structuraldamage to buildings; cracked roads and driveways; damage to curbs, gutters, and sidewalks; and heaving ofroads and canals. Expansive soils are chiefly derived from the weathering of clay-bearing rock formations andmay be residual (formed in place) or transported (usually a short distance) and deposited in a new location. Theprincipal transporting mechanisms are water or wind, but soil creep and mass-wasting processes may playimportant roles locally.For additional information about expansive soil and rock in the Zion National Park Geologic-Hazard Study Area,refer to the Problem Soil and Rock Hazards chapter in this report.
UTAH GEOLOGICAL SURVEYa division of Utah Department of Natural Resourcesin cooperation withNational Park Service
This geologic-hazard map was funded by the Utah Geological Survey and theU.S. Department of the Interior, National Park Service. The views andconclusions contained in this document are those of the authors and should notbe interpreted as necessarily representing the official policies, either expressedor implied, of the U.S. Government.Although this product represents the work of professional scientists, the UtahDepartment of Natural Resources, Utah Geological Survey, makes no warranty,expressed or implied, regarding its suitability for a particular use. The UtahDepartment of Natural Resources, Utah Geological Survey, shall not be liableunder any circumstances for any direct, indirect, special, incidental, orconsequential damages with respect to claims by users of this product.For use at 1:24,000 scale only. The Utah Geological Survey does notguarantee accuracy or completeness of data.
www.geology.utah.gov
Base map consists of U.S. Department of Agriculture 2006 National AgriculturalImagery Program natural color aerial photography and shaded relief generatedfrom digital elevation data acquired from the Utah Automated GeographicReference Center.
Universal Transverse Mercator Projection, zone 12North American Datum of 1983
REFERENCESChen, F.H., 1988, Foundations on expansive soils: Amsterdam, Elsevier, 463 p.Costa, J.E., and Baker, V.R., 1981, Surficial geology, building with the earth: New York, John Wiley & Sons, 498
International Code Council, 2009a, International building code: Country Club Hills, Illinois, 678 p.International Code Council, 2009b, International residential code for one- and two-family dwellings: Country Club
Keller, E.A., and Blodgett, R.H., 2006, Natural hazards – Earth’s processes as hazards, disasters, and
Lund, W.R., Knudsen, T.R., Vice, G.S., and Shaw, L, 2008, Geologic hazards and adverse construction
Mortensen, V.L., Carley, J.A., Grandall, G.C., Donaldson, K.M., Jr., and Leishman, G.W., 1977, Soil survey of
Nelson, J.D., and Miller, D.J., 1992, Expansive soils, problems and practice in foundation and pavement
Shelton, D.C., and Prouty, D., 1979, Nature’s building codes: Colorado Geological Survey Special Publication 12,
p.
Hills, Illinois, 870 p.
catastrophes: Upper Saddle River, New Jersey, Pearson Prentice Hall, 395 p.
conditions, St. George – Hurricane metropolitan area, Washington County, Utah: Utah Geological SurveySpecial Study 127, 105 p, 14 plates, digital video disk.
Washington County area, Utah: U.S. Department of Agriculture Soil Conservation Service and U.S.Department of the Interior Bureau of Land Management and National Park Service, 139 p., 95 plates, scale1:24,000.
engineering: New York, John Wiley & Sons, 259 p.
p. 37-40.
Approximate meandeclination, 2009
12 9'o
TRUE
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Map Location
1 0 10.5 MILE1000 0 1000 2000 3000 4000 5000 6000 7000 FEET
1 0 10.5 KILOMETER
SCALE 1:24,000
EXPLANATIONEXPANSIVE SOIL
EXPANSIVE ROCK
CONCEALED HIGHLY EXPANSIVE SOIL OR ROCK
High Hazard – Soils classified by the NRCS as having high hazard for volumetric change. These soilsare typically clay rich and have a LL >35, PI >15, and/or SCT value of >3 percent swell (Mortensenand others, 1977; Chen, 1988; Nelson and Miller, 1992). Soils having these characteristics are oflimited aerial extent in the study area, and are typically associated with the Petrified Forest Member ofthe Chinle Formation, other clay-rich bedrock units, and some weathered basalt flows.Moderate Hazard – Soils classified by the NRCS as having moderate hazard for volumetric change(LL 25–55, PI 5–35). The LL and PI values in this category overlap at their upper ends with soils inthe high hazard category. Chen (1988) recognized that while PI is an indicator of expansive potential,other factors also exert an influence, and therefore reported a range of PI values when categorizing asoil’s capacity to shrink or swell.Low Hazard – Soils classified by the NRCS as having low hazard for volumetric change (LL 0-40, PIfrom nonplastic to 15). The LL and PI values in this category overlap at their upper ends with soils inthe moderate hazard category. However, the low hazard category includes soils with highly variablepotential for volumetric change that do not fit easily into the moderate or high categories.No Data – Unconsolidated alluvial deposits in areas of upper Zion Canyon, Hop Valley, and LaVerkinCreek that may contain some clay-rich horizons subject to volumetric change, but a lack ofinformation about the physical characteristics of the deposits precludes hazard categorization. Thesedeposits are not included in the geotechnical database, and are mapped by the NRCS as chiefly RockOutcrop (NRCS soils-map unit RT) or Fluvaquents and Torrifluvents (NRCS soils-map unit FA) forwhich soil property estimations and engineering tests were not performed. Due to the variable natureof these deposits and a general lack of geotechnical data for them, we recommend site-specifictesting for expansive soil for all proposed construction within map areas having no data.
High Hazard – Bedrock units with high shrink/swell hazard, which include claystone horizons in theVirgin Limestone Member of the Moenkopi Formation, the Petrified Forest Member of the ChinleFormation, and the lower red beds of the Dinosaur Canyon Member and the Whitmore Point Memberof the Moenave Formation. We include landslides mapped within these rock units in the high-hazardcategory because the landslides contain debris from high-hazard bedrock units. These bedrock unitscontain an abundance of expansive clay minerals and are commonly associated with expansive rockproblems throughout southwestern Utah.Moderate Hazard – Bedrock units with moderate shrink/swell hazard, which include the Shnabkaiband lower, middle, and upper red members of the Moenkopi Formation; the Sinawava Member of theTemple Cap Formation; and the lower unit of the Co-op Creek Member and the Crystal Creek Memberof the Carmel Formation. These rock units are chiefly fine grained and contain alternating strata ofshale, claystone, mudstone, siltstone, sandstone, and limestone. Not all or even the majority of thesestrata contain expansive clay minerals; however, past experience in southwestern Utah has shownthat a sufficiently high percentage of strata do contain expansive clay that shrink/swell problems areoften associated with these bedrock units. We include landslides mapped within moderate-hazardrock units in this category.Low Hazard – Bedrock units with low shrink/swell hazard, which include the Timpoweap Member ofthe Moenkopi Formation, the Kayenta Formation, and the Winsor Member of the Carmel Formation.We consider these units to have a lower hazard than the bedrock units identified above; however, low-hazard units contain some fine-grained, clay-rich strata that may cause shrink/swell problems locally.
Concealed – Area suspected of having highly expansive soil or rock (>3 percent swell) in the shallowsubsurface (<20 feet), with little or no evidence of such material at the ground surface. The likelypresence of highly expansive materials in the shallow subsurface is based on the outcrop pattern ofthe Petrified Forest Member of the Chinle Formation, which indicates that the Petrified Forest Memberlikely underlies thin unconsolidated deposits in those areas. The Petrified Forest Member typicallycontains highly expansive shale and claystone, and past experience in southwestern Utah has shownthat when wetted, highly expansive soil or rock can cause damaging differential displacements at theground surface even when overlain by as much as 20 feet of nonexpansive material (Lund and others,2008). Therefore, we consider areas where the Petrified Forest Member may be present in theshallow subsurface to have a potential for highly expansive soil and rock problems despite the lack ofsurface evidence of such materials.
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