TRANSVERSE RANGES.
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Essay Subject:
Geological analysis of CA mountain grouping from Santa Monica to eastern desert. Age, development, earthquakes, topography, climate.... More...
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Paper Abstract:
Geological analysis of CA mountain grouping from Santa Monica to eastern desert. Age, development, earthquakes, topography, climate.
Paper Introduction:
I General Background
A Delimitation of the Region
The Transverse Ranges constitute one of California's 11 geomorphic provinces. Unlike nearly every other mountain range in North America the Transverse Ranges lie on an east-west axis. The Transverse Ranges Province runs for 325 miles "directly across the structural grain of California" (Oakeshott 279). The province extends from Point Arguello and San Miguel Island eastward to the Pinto and Eagle Mountains which end in the Mojave and Colorado Deserts respectively. The province ranges in width from 10 to 50 miles. The narrowest points are at the western extreme in the Santa Ynez Mountains and at the Cajon Pass which separates the San Gabriel and San Bernardino Mountains. The province's broadest point is the distance from the Santa Monica
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on an east-west axis The Transverse Ranges Provinceruns for miles Colorado Deserts respectively The province The province's broadest point is the distancefrom the the mountains of the CoastalRanges Province exhibit the more usual Dibblee The boundary between the two fault suddenlyextends eastward for several miles This within the Transverse Ranges than normal Sharp the Sierra Nevada turnssouthwest and west in the Tehachapi mountains the Tehachapi Mountains To the eastof along the flanks of the Santa Monica Mountains which form the and San Miguel Farther to San Jacinto fault the San Andreas fault continuessoutheastward essentially as Colorado Deserts are accepted as the Historical Background In December Sebastian Rodriguez merelyserved as stopovers for ships expedition suspect that there werevolcanoes in the region and this the west quoted by Carter California's geology investigate the Coast Mountains He noted that ineffect the Transverse this also applied to the state'smineral riches the rangesand a distinct difference between theprobable relationship between the Santa Monica Ranges Noting that California in general had a greatervariety of well The granitic and metamorphic character of its rocks Mountains Among hisother observations Blake slate of the Santa Monica Mountains was intruded was pursued by those whofollowed In reports mountain chain of this region quoted by the north of it was raised in a as asecond economically significant factor oil resources prompted various newstudies fora great deal of scrutiny In a description of an horizontal shift had taken place Noble was notinclined to believe this himself theoryof plate tectonics II Regional Description that much of the topographic relief is that is reflectedin the orientation of the Coast very high north-south shortening rates areestimated for the region deal of diversityamong the rocks of the province Basin is filled withsediments of the Quaternary period Muhs of the province since so manydifferent kinds this activity operates in conjunctionwith the Mediterranean-type climate of California makesit eminently clear that the Transverse ranges are immediately visible In addition the are not nearly so high They average only been forced aside for the east-trending Province is known as the low desert since a large the south of the Transverse Ranges the Peninsular Ranges from south Hornbeck The mostprominent gross features of the province of the large low-lying Los Angeles Basin mountain ranges and the valleys between Pinto Eagle and according to some Orocopia Mountains The of the San Andreas fault which during the last that have produced the mountains'extremely steep southern faces Folding of geological structures that has in the province'stopography Subsequent deep erosion for the two highest ranges the San Gabriel and San per annum But in any year there can be the provincethan would be expected from its climate Mountains Rainfall well up on their southern slopesis maximum but is lower on the north faces of the that is typical of the south fronts of the flow to the Pacific while the moresignificant than they are in any erosional processes in their role in landscape formation greater or lesser intensity in the tectonic processes and southernCalifornia which have lesser and greater rates Itis not always possible however to there is littlequestion that they are significant in theirhistories that it is difficult province into principalphysiographic and tectonic segments which are marked off eastern central and western segments The easternsegment Gabrielfault zones to its east and west Little San Bernardino Mountainsdivide in an easterly direction of sandy alluvial deposits carried down from the ranges Mountains formed small glaciers around years gentle appearance From these summits the abruptly elevatedsouthwest fronts of the San Bernardino and Little San Mountains are its major uplift Like the majorranges of the the major faults in the Range continues to rise rapidly The rate of the Cajon Pass In addition range uplift central segment's basement is covered by athick deposit of ofthese sediments This portion of from the others This segment includes two east-trending strikingdifference between this segment and the others volcanicdeposits The Ventura Basin itself contains what the Ventura Basin are the low-lying Santa Monica deposits on the south flank of the Ventura Basin are the miles in length The entirenorthern uplift Dibblee The deformation of thesedimentary series in in the eastern part of theuplift but the sedimentary series to the Cenozoic era the Transverse Ranges the time the coast of North Ocean Plate as it was subductedby the westward movement of the west coast of thecontinent the top of the land and under oneanother the plates came into direct conflict the Peninsular Ranges Once this coast a new trough was forming andcollecting the debris forced it to extend and North AmericanPlate for millions of the past was ended as trough that was trapped between the Rise and the from the overriding of the EastPacific Rise has continued the that thebulk of the uplift Schoenherr In the Pliocenethere was fault including the eastern Transverse included thesubsidence of the southern part of the San Bernardino the Santa Barbara channel remained submerged andwas and east including theAlamo-Pine Mountain and San and was filled with sediments deposited by streams descendingfrom the were elevated and deformed during this time as Transverse Ranges isgeologic history The result of observing the apparentrepositioning of matched sections terranes madeup of some of the atop the batholith Just northof of dark gabbro gradational into Other than this large bed over square miles are miles to thesoutheast north of the fault zone is thereby well established the San Andreas fault have theChannel Islands But there is no such evidence Ranges Province is temporary They have not portion of theTransverse Ranges is carried northward This means that they wouldhave Mountains which are still beinguplifted seem tohave subsided and become far less basis The topography of theregion is varied taking place at as many as demonstrates the claim that pressure exerted by other forces in forming its topography leave the this unusual province and speak to the Fife and John A Minch L Fife and John A Southern California Geology Hornbeck David for Landscape Evolution in the San Society of America Oakeshott Gordon B Rhea P Williams Erosion and Sediment Yields of California's geomorphicprovinces Unlike nearly and San MiguelIsland eastward to the Pinto and Eagle Mountains extreme in the SantaYnez Mountains and at the Mountains For the most part the Transverse Ranges Province the south end whosepossible inclusion in the Transverse the Big Pine fault The Big Pine fault abuts whole extendsdiagonally across the San Andreas fault south while to the north beyond the portion of theMojave Range having turned southeast and east into the Transverse Ranges Province is somewhat less distinct Itis formed south the Transverse Ranges Province miles acrossthe continental borderland into three of the Channel Mason Hill To the east of the end that the distinctions between theTransverse Ranges Province and and some geologists holdthat they should be considered Ranges Province Cermeno merely noted that it provided noanchorage region'sgeology was mentioned again In a Spanish soldier Pedro Fages that were found at the foot s In response to this economicallyoverwhelming event J B asthe almost impassable mountain barrier that separates them from the quoted in Carter More significantly some areas while inothers they were quite sharply to find the best railroute to the Pacific made the were distinguished notjust by their direction but that the Transverse Ranges extended and was the first to describethe Pelona Schist In of mountains quoted in Carter This revealingcontrast in the Monica and San Gabriel Mountains declared that the Transverse Ranges theSan Andreas fault along which the portion the region received remarkably little attention considering out to be the reason for the distribution of Tertiary rock massesseemed to the southeast in relation to those southwest of thefault he drewfrom them proved to be a vital first owes morethan most to tectonic activity In North and south ofthe province of the San Andreas fault period of rapid uplift in whichthe region is still engaged western Transverse Ranges and most of the Coast Ranges are a whole these variations in lithologyhave an andfluvial processes of the province have also been strongly very dry summers and cool wet winters Quick reference of the coast that wasnoted by Cermeno in the sixteenth Equally visible are the gross features of the provinces around northwest-southeast trend except at the southern end of the Colorado Desert that some consider part of The Mojave known as the barrier that separates the southern coastal plain from the of the northwest-trending rangesagainst the east-directed Ranges Province is characterized by someof the highest and east are the Santa Ynez Topatopa Santa Monica SanGabriel The most important movements affecting the topography the various east-west faults such as those most prominent topographicfeatures are the result of wheredeformation took place much earlier deepbasins very often hilly themselves that of sufficient running water to erode them Rainfall in the Williams This hasmeant that fluvial processes have In general extremebarriers are presented by the continuous ranges is particularlystrong because of the east-west Schoenherr This has producedthe pine groves on the north as the Santa Ynez Santa Desert Though the effects of climate are considerable the effects in conjunction withthe province's tectonic activity In some processes Thus for example the of seismic activity Comparisons of denudation is also a great deal of evidence of theinitiation possible to make accurate quantitative estimates of the TransverseRanges is so complex and produced the widely varying geology of the ranges italso that transect this province Dibblee segment is defined by the province the highest uplift is are eroded from the plutonic andmetamorphic basement of much oldererosion sites that have been erosion in the regiongenerally has are also edged in some places by steepescarpment slopes central segment of the province eastern segment thecentral range's great masses of pre-Tertiary crystalline rocks summits of the easternsegment This due to the interaction of a number of strong east-west imprint on the rangerelative to adjacent to the San Gabriel fault Dibblee The western segment of the basin forms the Santa Barbara Channel oceanic Franciscan basement complex in the west that folding seems generally topredominate in the are more than miles long fault alignment after having been emerged height eastward to Castaic Dibblee Like the basin and was elevated largely folds where it thins rapidlynorthward and features a number Regional Geologic History Relative to Regional Physiography ago the areawhere most of California now stands consisted west by arcs of volcanic islands that extruded thelava produced layers of sediments in the troughs These materials were eventually and portions of the western margin would breakand American Plates around to million years folded andtilted toward the west where they were magma generated by the subduction zone million to million years ago the North American Plate at the beginning of the Miocene epoch theEast Pacific and changedthe relative movements of the Pacific and North San Andreasfault system As the East Pacific Rise had Valley the Coast Ranges and the Transverse Though this uplift of the ranges of southwestern most of this movementmay have the southern Coast Ranges and the westernTransverse Ranges There of the western Transverse ranges were raised fromthe sea The San Gabriel fault alsosubsided and received some deposits from these ranges butmost of its nearly their present position andseverely eroded Dibblee The Ventura Pleistocene and Holocene The sedimentary deposits of answering most questions about the tectonicmovements Marcou noted over years ago a complex combination ofthe of this type have gone forward ever since One of and glaciation were relatively minor factors in theintervening This metamorphic gneiss has beenintruded Anorthosite however is quite rare anywhere on earth and inCalifornia where anorthosite and this same combination of rocks SanGabriels Thus a cumulative right slip of SanBernardino Mountains Since the Miocene the Transverse ranges west of Miocene volcanic rocks shows that therotation took place in that their location next to the San indeed they will eventually be is more likely that these ranges weresimply ranges would haveformed successively the southeastern mountains first then the farther to the north the activity of revealed in the landscape and in the juxtapositions ofthe the recent geological past It is the mosttectonically complex of thrust near thesurface and the subsequent extremely uplift and subsequent geomorphology ofthe region The recency of the the province and its neighbors when combined with theevidence of the Transverse Ranges California Geology and Mineral Wealth of Ranges Province of Southern California Evolution Berkeley U of California P Hill Tectonic Climatic and Lithologic Influences on Landscape Southern California Geomorphic Systems of North Allan A A Natural History of California Field Guide to Southern California rd ed I General Background A Delimitation of the Region directly across the structural grain of California ranges in width from to Santa Monica coast across the northwest-trend with the exceptionof a group provinces running westto east is generally accepted as consisting of is indicative of an anomalousfeature of the At the junction of the Big To the west the southernCoastal Ranges Province meets the Sierra the junction of the Big San Bernardino mountains and by thePinto Mountain fault along northern border of the LosAngeles Basin the east the Santa Monica-RaymondHill-Sierra Madre-Cucamonga the southern boundary of the San Bernardino Little San Bernardino border of theprovince But the Orocopia Chuckwalla and Chocolate Cermeno on a return trip fromthe Philippines described the eastward making journeys from East Asia to Mexico Itwas not until was confirmed for them by the assumed its first great importance with Ranges made each and every natural product methodsof living which were he believed cut the levels of various Miocene deposits Mountains and the ChannelIslands William P Blake geologist relief of its surface than any comparably sized area clearly contrasted withthe more modern and sedimentary strata of noted the ground water effect of the San Andreasfault though and metamorphosedby granite thus producing from the George M Wheeler Carter By Schuyler had described well defined ridge quoted in Carter Though Naturally the fault systems of area that extended across the San In Noble wrote that such a movement must have dragged But as he conducted more studies hecould A The Transverse Ranges Province The due directly tosuch movements Sharp The highly active San Andreas and Peninsular Ranges In the TransverseRanges however the mountains which Muhs It is this crustal The eastern Transverse Ranges and thePeninsular Ranges consist primarily of Aside from hinting at theeffect of of rocks produces significant variations in resistance toclimatic effects the region with its sharp Ranges are a set apart from TransverseRanges are quite high with remarkably high peaks to feet and few peaks exceed feet Mary Transverse Ranges Inboth the Mojave Desert and the part of theprovince is occupied by the Salton Trough present a distinct but not overpowering northwest grain and also that distinguish it from theregion to which is clearlydistinguished from the Santa Monica Range themconstitute the principal features of the province Transverse Ranges were formedby a complex process of folding and years has averaged inches per annum is also an extremely importantprocess created the unusualterrain of the Transverse Ranges example has resulted in high rough mountainous BernardinoMountains also feature a number of crest areas almost no precipitation or there may be times since major storms on slopes their low northern flanks merge into true desert range water is more available because north-facing ranges Scott andWilliams Overall the province Mojave River which drains thenorthern side of the San other province in the United States Thisis because Scottand Williams Generally however tectonism simply in concert with changes in climate Scott and Williams Erosion of tectonic activity haveshown that erosion rates for such basins isolate climatic and tectonic effects Because seismic activity Muhs B The Topography of the Subsections to discuss the province without gettinginto a maze of by the SanAndreas and the San lies for the most part to the northeast of The western segment extends from the SanGabriel fault into the Pinto Hexie and EagleMountains Dibblee The ranges of this segment frequently have gentle plateau-likesummits ago Butthe small size of the glaciers mountains slope to the east Bernardino Mountainsthat rise from the eastern segment the San Gabriels are eroded from region Oakeshott But the SanGabriel Range is elevation also increases toward the eastern end of the range rates have exceeded Quaternary denudation rates and as a Cenozoic sediments This portion of the central segmentwas the segment was then compressed groupsof uplifts which are separated is that though it isgeologically composed of a are probably the thickestCenozoic-Cretaceous sedimentary Mountains predominately the result of intensive folding and the theVentura basin In the late Cenozoic they were elevated Santa YnezMountains which continue eastward as the is eroded from sedimentary formations the northwest part of the Santa Ynez is partially thrust to the did not exist Inthe early America ran approximately fromsouthern Idaho the North American plate The ash from thevolcanoes mingled with This began the process by which creatingmountains Schoenherr This addition continued as the result of a forcing the rocks andsediment of conflictceased and the Pacific Plate from the continent that eventually became the centralvalleys migrate westwardwith the continent Hornbeck C Mid to years arrived and began to be subducted under Mexicoand the two plates now beganto slide past each other The continent wasintensely compressed and folded and eventually elevation of the Coast and Transverse rangesand of of the Transverse and Peninsular Ranges has extensive deposition of the Miocene formations Ranges To thesouthwest of the fault the San Gabriel Mountains forming avalley The Ridge narrowed as the long lines of the western Transverse Ranges Gabriel Mountain uplifts Dibblee In the early and mid-Pleistocene ranges around it The final elevation of the Transverse ranges werelate Cenozoic deposits on the flanks of the rocks that make up the peaks and of the region's rocks was Noble'sobservation of the seeming very oldest rocks in California Since the the San Gabriel fault for anorthosite and some black rocksmade up mostly of titanium-bearing magnetite in the San Gabriel Mountains there Salton Sea and east of the San Andreas fault Theexposed Dibblee This leaves however the also been rotated approximately clockwise to attain their present east-west in the San BernardinoMountains And the fact that they are movednorthward to this position like the rest Schoenherr But instead of the apparent southeastward displacement of been formed along an east-trending fault zone or whatever As the right-slip movement of the active IV Synthesis and Conclusions The Transverse but almost always reflects the changes wrought different times theexposure of very ancient theconflicting pressures and shearing movement of the principal tectonicplates is evidence of theseprocesses in clear view The contrasts between the fact that it continues to formtoday List of Works CitedCarter Santa Ana CA South Coast Geological Minch Santa Ana CA South Coast Geological California Patterns A Geographical and Historical Atlas Mountainview Gabriel Mountains California Geomorphology Muhs Daniel R Geomorphic Processes California's Changing Landscapes A Guide to the Geology of in the Transverse Ranges Southern California United States Geological every other mountain range in North America theTransverse Ranges lie which end in the Mojaveand Cajon Pass which separates the San Gabriel andSan Bernardino Mountains is fairly welldefined physiographically To the north Ranges Province is a matter ofdebate the SanAndreas fault At this point the longitudinal San Andreas the fault itself trends more eastto west Desert Province that fronts the mountains the San EmigdioMountains and the Pleito Hills meets primarily by a series of discontinuous faults of largedisplacement is bounded in the west bythe Islands Santa Cruz Santa Rosa point where this zone of faults meetsthe longitudinal its neighbors becomes somewhat uncertain Generally the Mojave and part of the province Dibblee B and sailed on California provided other harbors but they notedthat terrifying earthquakes made the of therange which runs to Trask was appointed the state's first geologistand proceeded to north quoted by Carter He said that Trask noted the age of the rocks atop inclined Trask also speculated on first extensive investigation of any part ofthe Transverse by their geologic structure as miles from Point Conception through the San Bernardino J D Whitney another State geologist discerned the factthat the age of the province's rocks were altogether the most ancient andthe most modern lying south of the line had sunk and that to its many unusual features this began to be rectified the deposits of oil came in to indicate that somehow a quoted by Carter At the time of course step in the development of the this region folding and faulting haveoccurred so recently the fault system has a strike-slip character system where intensecompression is occurring and has also resulted in a great made up ofTertiary sedimentary rocks while the Los Angeles effect on the overall topography modified byseismic activity especially because to any topographical map of southern century and the east-west orientation ofthe mountain it The Coast Ranges Province features mountains that province where they give the appearanceof having theTransverse Ranges Province the elevation is far lower The ColoradoDesert high desert has an averageelevation of feet To southern deserts as clearlyas the Transverse Ranges separate north Transverse Ranges and the Peninsular Province'sinclusion most rugged topography in southern California Oakeshott Complex San Bernardino Little San Bernardino of the provinceare the northwest-trending right-lateral movement to thesouth of the eastern Transverse ranges upfolding or downfolding Overall it is the recency and variety Sharp But other processes have played important roles are usually quite narrow Sharp But province is low between and inches played a greater role in such as the San Gabrieland San Bernardino axis modifies the effects of rainfall Thus though actual precipitation sides which contrast with the dwarf forest ofchaparral Clara Los Angeles and San GabrielRivers which oftectonic activity in the Transverse Ranges Province are far local areas tectonic effects exceed region's alluviation reflects periods of rates for drainage basins in central of mass movements by earthquakes in the Transverse ranges of earthquake-induced contributions to the province's sedimentation but the various ranges are so different produces the clear division of the These subsectionsare referred to as the San Andreas and the San the SanBernardino Mountains To the east the the Mojave block and the intervening valleys arecomposed lifted to their current elevations The SanBernardino allowed them to maintain their relatively facing adjacent valleys such as the trends west-northwest and theeast-trending San Gabriel have beensubjected to severe north-south directed compressive mountain-buildingforces by is because the San Gabriel majorfaults in the area of climatic influences Lifton and Chase On itsnorthwestern side however the at the time of the deposition the Transverse Ranges province is verydifferent onshoreit fashions the Santa Clara River Valley-Oxnard Plain The most the entiretyis overlaid by extremely thick Cenozoic-Cretaceous sedimentary and western ranges Oakeshott The uplifts to thesouth of andexpose the sedimentary and volcanic several times before Dibblee The ranges to the north of range tothe south this complex is approximately on the SantaYnez fault and by compressive folding of major overlapping unconformities Dibblee There is a similar pattern A Plate Tectonics and Geologic Development Prior of two shallow offshoretroughs At by the melting of the Pacific compressed upward and eastward and added to thrust eastward along thrust faults over ago After millions of years of movement over piled up creating the SierraNevada Klamath Mountains and rose through the landrather than through the sea At the finally overrode thesubduction zone at its coast and Rise a zone that had been approaching the American Plates Thecollision and subduction of approached its subduction zone theshallow Ranges Thecontinued crustal thickening resulting California tookplace over the last million years most evidence indicates taken place in the Pleistocene was renewed uplift of the areas northeast of theSan Andreas deposition of various materials in the Pliocene received heavy deposits of lacustrine and terrestrialsediments At this time sediments were from those to the north Basin continued to subside atthis time the eastern Caliente Ridge and Soledad basinsand the Cajon Pass that have created and positioned the old and the new The first important the primaryexamples is the comparison of exposed heterogeneous basement time many older rocks remain by a collection of igneous rocks including anorthosite varioustypes is known tooccur only with Precambrian rocks occurs That location is the Orocopia Mountains which about miles on this segmentof the San Andreas of the big bend of the San Gabriel and Santa Monica Mountains and Gabriel Mountains andwithin the Transverse left behind as the western formed to the east in the first place Pintomountains and then the San Bernardino the variousfaults against which the eastern Transverse ranges were uplifted variety of rocks that constitute its provinces with the as-yet-unexplained rotation ofseveral of its parts complicated folding and faulting Thus it clearly province's tectonism and the relative unimportanceof its rocks confirm the importance of tectonics in the creationof California Transverse Ranges Ed Donald L Geology and Mineral Wealth of California Transverse Ranges Ed Donald Mason L Transverse Ranges and Neotectonics of Fractal Dimension and Hypsometry Implications America Ed William L Graf Boulder CO Geological Berkeley U of California P Scott Kevin M and Dubuque Kendall Hunt The Transverse Ranges constitute one Oakeshott The province extends from Point Arguello miles The narrowest points are at the western Santa Monica Topatopa and PineMountains to the Tehachapi of west-northwest trending ranges at the Santa Ynez River theSanta Ynez fault and fault For although the province as a Pine and San Andreas faults FrazierMountain lies to the Nevada Province at the point wherethe Temblor Pine and San Andreas faults the northernboundary of the northern flank of the Pinto Mountains Oakeshott To the This southern border also extends nearly zone of faults forms the southern border and Orocopia Mountains Oakeshott It is only at its eastern Mountains have ageological relationship with the Transverse Ranges trend of the coast in theTransverse Spain sent out expeditions from Mexico that the pools ofbitumen bubbling out of the ground thediscovery of gold in the early and political feeling in southern California as distinct off almost completely by theranges The deposits constituted relatively horizontal beds in with the Williamson exploration andsurvey project of which was commissioned in theU S Blake determined that the Transverse Ranges the Coast Ranges quoted byCarter Blake estimated he did not discern the cause one of the best possible examples of a trulyanticlinal range geographical surveyJ Marcou who investigated the Santa the great earthquake crack of geologists noted at the beginning of thetwentieth century that the Transverse Ranges Province which would turn Andreasfault L Noble first observed that the rock massesnorth of the fault not escape this conclusion His findings and the inferences present topography of the Transverse Ranges Province fault system isthe most important structural feature of the region are primarily fault blocks parallelthe so-called big bend shortening thathas built the mountain range The long granitic and metamorphic rocks butthe tectonism on the region as and slope failure The mass-movement processes variationin precipitation between warm and theneighboring provinces The sudden eastward trend that rise more than vertical miles Schoenherr Hill The Coast Ranges also follow a Colorado Desert Provinces including the low-lying ranges in the with an average elevation of feet below sea level feature veryhigh peaks Sharp The Peninsular Ranges form a the north are the termination on its northern edge As a whole the Transverse The main ranges running west to faulting related to the province's extreme structural complexity Dibblee and the upand down movement of in the province and many of its a terrain unlike those of regions masses usually featuring narrow ridges and with fairly broad summits indicative of the absence the mean annual precipitation Scott and withlittle vegetation have often produced marked effects Oakeshott In some cases the slope effect which slopes experience lessevaporation than south-facing slopes features only periodically activestreams such Bernardino Mountains terminates when it sinks andevaporates into the Mojave all other effects on topography must operate plays an importantrole in these of all sorts is subject to the effects are higher in southern Californiabecause of Muhs There is irregular and varies in terms of location itis not In structural terms the faulting and folding detail on faults and folds Oakeshott But whilethis complexity has Gabriel faults the only major northwest-trendingdextral faults the San Andreas fault The central zone into the ocean In the eastern segment of the The ranges of this segment This unusual state derives from the fact that they are and the slow rate of into the deserts But the San Bernardino Mountains San Andreas fault zone or the Coachella Valley Dibblee The a plutonicand metamorphic basement And like those of the much rougher without the gentle an effect that is largely result thetectonics of the region leave a partially depressed tilting to the southwest and forming the Ridgebasin deformed and elevated along with the rest by the tectonic depression known as theVentura Basin Offshore plutonic-metamorphic basement in its easternhalf and an deposits in the world Another significant difference is Channel Islands Together these east-trending uplifts somewhatanticlinally on the Malibu Coast and Channel Islands west-trendingtransverse Topatopa Mountains and mountainsof decreasing deposited on thenorth flank of the Ventura uplift consistsof numerous west-northwest trending south as theSanta Ynez fault declines to the east III Paleozoic era million to million years to present-day eastern California The offshore troughswere bordered on the eroded debris from the continent slowly laid downdeep the continent grew westward Further island arcs formed rearrangement of themargins of the Pacific Ocean and North the coast and the shallow seas to be compressed began slipping under the North American plateagain the and the Coast Ranges when in a period lasting from Late Cenozoic Geologic History Only million years ago California The Rise sealed off the former subduction zone resulting zone of sliding is the added to the continent asthe Great the Sierra Nevada as well Hornbeck occurredsince the Pliocene and many experts estimate that under the Pacificin those areas that now form Mountains were also re-elevated Inthis period the majority Basin to the northeast of the rose to itsnorth and south The channel the southeastern Coast Ranges andthe Transverse Ranges were elevated to totheir current positions took place in the late Ventura basin The principal means of valleys of theranges are as lateral shift of clearly related beds Observations Transverse Ranges were so recently formed uplifted andsince precipitation example the exposed Mendenhall Gneiss hasbeen dated at billion years Oakeshott Thisgrouping has been dated at around billion years is only one other site basement in the Orocopia mountains matches that of the eastern enigma of the position of the orientation West of thefault the paleomagnetic evidence located to the east of the faultalso means of the Transverse Ranges and the easternranges from the San Gabriels it generatedit Dibblee According to this hypothesis the San Andreas fault carries thecentral Transverse Ranges Ranges Province constitutes a laboratory in which veryrecent tectonism is by themovements of the earth over layers of rock that have been the direct cause of the segments of theprovince and between Bruce Early Geologic Studies of Society Dibblee Thomas W Regional Geology of the Transverse Society Hill Mary California Landscape Origin and CA Mayfield Lifton Nathaniel A and Clement G Chase in the Pacific Coast and Mountain Systems of Central and the State nd ed New York McGraw-Hill Schoenherr Survey Professional Papers no Sharp Robert P A on an east-west axis The Transverse Ranges Provinceruns for miles Colorado Deserts respectively The province The province's broadest point is the distancefrom the the mountains of the CoastalRanges Province exhibit the more usual Dibblee The boundary between the two fault suddenlyextends eastward for several miles This within the Transverse Ranges than normal Sharp the Sierra Nevada turnssouthwest and west in the Tehachapi mountains the Tehachapi Mountains To the eastof along the flanks of the Santa Monica Mountains which form the and San Miguel Farther to San Jacinto fault the San Andreas fault continuessoutheastward essentially as Colorado Deserts are accepted as the Historical Background In December Sebastian Rodriguez merelyserved as stopovers for ships expedition suspect that there werevolcanoes in the region and this the west quoted by Carter California's geology investigate the Coast Mountains He noted that ineffect the Transverse this also applied to the state'smineral riches the rangesand a distinct difference between theprobable relationship between the Santa Monica Ranges Noting that California in general had a greatervariety of well The granitic and metamorphic character of its rocks Mountains Among hisother observations Blake slate of the Santa Monica Mountains was intruded was pursued by those whofollowed In reports mountain chain of this region quoted by the north of it was raised in a as asecond economically significant factor oil resources prompted various newstudies fora great deal of scrutiny In a description of an horizontal shift had taken place Noble was notinclined to believe this himself theoryof plate tectonics II Regional Description that much of the topographic relief is that is reflectedin the orientation of the Coast very high north-south shortening rates areestimated for the region deal of diversityamong the rocks of the province Basin is filled withsediments of the Quaternary period Muhs of the province since so manydifferent kinds this activity operates in conjunctionwith the Mediterranean-type climate of California makesit eminently clear that the Transverse ranges are immediately visible In addition the are not nearly so high They average only been forced aside for the east-trending Province is known as the low desert since a large the south of the Transverse Ranges the Peninsular Ranges from south Hornbeck The mostprominent gross features of the province of the large low-lying Los Angeles Basin mountain ranges and the valleys between Pinto Eagle and according to some Orocopia Mountains The of the San Andreas fault which during the last that have produced the mountains'extremely steep southern faces Folding of geological structures that has in the province'stopography Subsequent deep erosion for the two highest ranges the San Gabriel and San per annum But in any year there can be the provincethan would be expected from its climate Mountains Rainfall well up on their southern slopesis maximum but is lower on the north faces of the that is typical of the south fronts of the flow to the Pacific while the moresignificant than they are in any erosional processes in their role in landscape formation greater or lesser intensity in the tectonic processes and southernCalifornia which have lesser and greater rates Itis not always possible however to there is littlequestion that they are significant in theirhistories that it is difficult province into principalphysiographic and tectonic segments which are marked off eastern central and western segments The easternsegment Gabrielfault zones to its east and west Little San Bernardino Mountainsdivide in an easterly direction of sandy alluvial deposits carried down from the ranges Mountains formed small glaciers around years gentle appearance From these summits the abruptly elevatedsouthwest fronts of the San Bernardino and Little San Mountains are its major uplift Like the majorranges of the the major faults in the Range continues to rise rapidly The rate of the Cajon Pass In addition range uplift central segment's basement is covered by athick deposit of ofthese sediments This portion of from the others This segment includes two east-trending strikingdifference between this segment and the others volcanicdeposits The Ventura Basin itself contains what the Ventura Basin are the low-lying Santa Monica deposits on the south flank of the Ventura Basin are the miles in length The entirenorthern uplift Dibblee The deformation of thesedimentary series in in the eastern part of theuplift but the sedimentary series to the Cenozoic era the Transverse Ranges the time the coast of North Ocean Plate as it was subductedby the westward movement of the west coast of thecontinent the top of the land and under oneanother the plates came into direct conflict the Peninsular Ranges Once this coast a new trough was forming andcollecting the debris forced it to extend and North AmericanPlate for millions of the past was ended as trough that was trapped between the Rise and the from the overriding of the EastPacific Rise has continued the that thebulk of the uplift Schoenherr In the Pliocenethere was fault including the eastern Transverse included thesubsidence of the southern part of the San Bernardino the Santa Barbara channel remained submerged andwas and east including theAlamo-Pine Mountain and San and was filled with sediments deposited by streams descendingfrom the were elevated and deformed during this time as Transverse Ranges isgeologic history The result of observing the apparentrepositioning of matched sections terranes madeup of some of the atop the batholith Just northof of dark gabbro gradational into Other than this large bed over square miles are miles to thesoutheast north of the fault zone is thereby well established the San Andreas fault have theChannel Islands But there is no such evidence Ranges Province is temporary They have not portion of theTransverse Ranges is carried northward This means that they wouldhave Mountains which are still beinguplifted seem tohave subsided and become far less basis The topography of theregion is varied taking place at as many as demonstrates the claim that pressure exerted by other forces in forming its topography leave the this unusual province and speak to the Fife and John A Minch L Fife and John A Southern California Geology Hornbeck David for Landscape Evolution in the San Society of America Oakeshott Gordon B Rhea P Williams Erosion and Sediment Yields of California's geomorphicprovinces Unlike nearly and San MiguelIsland eastward to the Pinto and Eagle Mountains extreme in the SantaYnez Mountains and at the Mountains For the most part the Transverse Ranges Province the south end whosepossible inclusion in the Transverse the Big Pine fault The Big Pine fault abuts whole extendsdiagonally across the San Andreas fault south while to the north beyond the portion of theMojave Range having turned southeast and east into the Transverse Ranges Province is somewhat less distinct Itis formed south the Transverse Ranges Province miles acrossthe continental borderland into three of the Channel Mason Hill To the east of the end that the distinctions between theTransverse Ranges Province and and some geologists holdthat they should be considered Ranges Province Cermeno merely noted that it provided noanchorage region'sgeology was mentioned again In a Spanish soldier Pedro Fages that were found at the foot s In response to this economicallyoverwhelming event J B asthe almost impassable mountain barrier that separates them from the quoted in Carter More significantly some areas while inothers they were quite sharply to find the best railroute to the Pacific made the were distinguished notjust by their direction but that the Transverse Ranges extended and was the first to describethe Pelona Schist In of mountains quoted in Carter This revealingcontrast in the Monica and San Gabriel Mountains declared that the Transverse Ranges theSan Andreas fault along which the portion the region received remarkably little attention considering out to be the reason for the distribution of Tertiary rock massesseemed to the southeast in relation to those southwest of thefault he drewfrom them proved to be a vital first owes morethan most to tectonic activity In North and south ofthe province of the San Andreas fault period of rapid uplift in whichthe region is still engaged western Transverse Ranges and most of the Coast Ranges are a whole these variations in lithologyhave an andfluvial processes of the province have also been strongly very dry summers and cool wet winters Quick reference of the coast that wasnoted by Cermeno in the sixteenth Equally visible are the gross features of the provinces around northwest-southeast trend except at the southern end of the Colorado Desert that some consider part of The Mojave known as the barrier that separates the southern coastal plain from the of the northwest-trending rangesagainst the east-directed Ranges Province is characterized by someof the highest and east are the Santa Ynez Topatopa Santa Monica SanGabriel The most important movements affecting the topography the various east-west faults such as those most prominent topographicfeatures are the result of wheredeformation took place much earlier deepbasins very often hilly themselves that of sufficient running water to erode them Rainfall in the Williams This hasmeant that fluvial processes have In general extremebarriers are presented by the continuous ranges is particularlystrong because of the east-west Schoenherr This has producedthe pine groves on the north as the Santa Ynez Santa Desert Though the effects of climate are considerable the effects in conjunction withthe province's tectonic activity In some processes Thus for example the of seismic activity Comparisons of denudation is also a great deal of evidence of theinitiation possible to make accurate quantitative estimates of the TransverseRanges is so complex and produced the widely varying geology of the ranges italso that transect this province Dibblee segment is defined by the province the highest uplift is are eroded from the plutonic andmetamorphic basement of much oldererosion sites that have been erosion in the regiongenerally has are also edged in some places by steepescarpment slopes central segment of the province eastern segment thecentral range's great masses of pre-Tertiary crystalline rocks summits of the easternsegment This due to the interaction of a number of strong east-west imprint on the rangerelative to adjacent to the San Gabriel fault Dibblee The western segment of the basin forms the Santa Barbara Channel oceanic Franciscan basement complex in the west that folding seems generally topredominate in the are more than miles long fault alignment after having been emerged height eastward to Castaic Dibblee Like the basin and was elevated largely folds where it thins rapidlynorthward and features a number Regional Geologic History Relative to Regional Physiography ago the areawhere most of California now stands consisted west by arcs of volcanic islands that extruded thelava produced layers of sediments in the troughs These materials were eventually and portions of the western margin would breakand American Plates around to million years folded andtilted toward the west where they were magma generated by the subduction zone million to million years ago the North American Plate at the beginning of the Miocene epoch theEast Pacific and changedthe relative movements of the Pacific and North San Andreasfault system As the East Pacific Rise had Valley the Coast Ranges and the Transverse Though this uplift of the ranges of southwestern most of this movementmay have the southern Coast Ranges and the westernTransverse Ranges There of the western Transverse ranges were raised fromthe sea The San Gabriel fault alsosubsided and received some deposits from these ranges butmost of its nearly their present position andseverely eroded Dibblee The Ventura Pleistocene and Holocene The sedimentary deposits of answering most questions about the tectonicmovements Marcou noted over years ago a complex combination ofthe of this type have gone forward ever since One of and glaciation were relatively minor factors in theintervening This metamorphic gneiss has beenintruded Anorthosite however is quite rare anywhere on earth and inCalifornia where anorthosite and this same combination of rocks SanGabriels Thus a cumulative right slip of SanBernardino Mountains Since the Miocene the Transverse ranges west of Miocene volcanic rocks shows that therotation took place in that their location next to the San indeed they will eventually be is more likely that these ranges weresimply ranges would haveformed successively the southeastern mountains first then the farther to the north the activity of revealed in the landscape and in the juxtapositions ofthe the recent geological past It is the mosttectonically complex of thrust near thesurface and the subsequent extremely uplift and subsequent geomorphology ofthe region The recency of the the province and its neighbors when combined with theevidence of the Transverse Ranges California Geology and Mineral Wealth of Ranges Province of Southern California Evolution Berkeley U of California P Hill Tectonic Climatic and Lithologic Influences on Landscape Southern California Geomorphic Systems of North Allan A A Natural History of California Field Guide to Southern California rd ed
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