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The San Andreas Fault of the Salton Trough Region, CA

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The San Andreas Fault of the Salton Trough Region, CA I SBCMA Spec . Pay . 93-i Putt 69 The San Andreas Fault of the Salton Trough Region, California, as Expressed on Remote Sensing Data FRANCESCO V. CORONA Energy Resources Technology Division, P . O. Box 76 , Brea, California 92621 FLOYD F. SAB(NS, JR. Remote Sensing Enterprises, 1724 Cdeste Lane, Fullerton . California 92633 ABSTRACT The San Andreas fault and related structures in the Salton trough region are readily expressed on Landsat images and high-altitude aerial photographs, having diagnostic surface characterisitics that are typical of a wrench-fault assemblage . These characteristics include a principal strike-slip displacement zone that is relatively straight and long, inconsistent structural relief along major wrench faults, the occurrence of en echelon structures adjacent to the.. major strike-slip faults, and lateral offset of structural, natural, and man-made features. Wrench-fault transgression and transtension occur in places along the San Andreas fault system, recognized respectively by the dominance of contractional or extensional structures. All of these surface manifestations are clearly discriminated on the remote sensing data and define criteria that distinguish wrench-fault assemblages from other structural styles . INTRODUCTION and others. 1973; Harding, 1974: Reading, 1980; Christie-Blick and The southern extent of the San Andreas right-lateral, strike-slip Biddle. 1985; Harding, 1990) . Wrench-fault assemblages have unique fault lies along the northeastern margin of the Salton trough in structural characteristics that differentiate them from other styles of southern California (Figure I)_ This fault is tectonically active, well deformation (Harding and Lowell . 1979; Lowell, 1990) . Likewise. exposed, and well documented in this region (many authors; e.g., wrench-fault assemblages have distinguishing surface manifestations Crowell, 1962; Dibblee. 1977; Crowell and Sylvester. 1979; Sylvester. that can be detected and analyzed using remote sensing data (Corona, 1988; Hutton and others. 1991) . thus offering an ideal locality to 1993) . study the San Andreas fault and the structural assemblage that is The San Andreas wrench-fault system in the Salton trough region commonly associated with wrench-fault tectonics (Figure 2 ; Wilcox is profoundly displayed on remote sensing data (Corona and others, 1993). Examination of this fault system using these data yields diagnostic surface characteristics that define criteria to ttsvaw distinguish a wrench-fault structural assemblage from other structural styles. The following discussion describes the identification criteria of wrench-fault assemblages from remote sensing data utilizing Landsat Thematic Mapper images and high-altitude aerial photographs along this Salton trough segment of the San Andreas fault system . AREAS OF INVESTIGATION Four areas along the San Andreas fault system in the Salton trough are selected to show the diagnostic surface characteristics of wrench-fault assemblages as expressed on remote sensing data (see Figure 1) . These areas are the Indio . Mecca, and Dunnid hills, and the Imperial Valley . The Indio Hills display classic neotectonic wrench-fault morphology, whereas the Mecca Hills reveal a suite of wrench-related structural elements. Wrench-fault rranspression dominates the Dunnid Hills, and uanstension is prevalent in the Imperial Valley. These areas conjointly constitute most of the structural characteristics that typify a wrench-fault structural style . In turn, these structural characteristics provide the criteria for the identification of wrench-fault assemblages from remote sensing or any geologic-map data . The compilation of these criteria are summarized at the end of this discussion . Figure 1. Location map of the Salton trough region of southern California showing the major strike-slip (wrench) fault systems and areas of Indio Hills investigation (Figures 3, 4, 5, and 7). These areas are, from northwest to southeast, the Indio Hills, the Mecca Hills, the Durmid Hills, and the The Indio Hills form a low northwest-trending ridge along Imperial Valley. IF, Imperial fault the northeastern margins of the Coachella Valley and Salton ; SAF, San Andrcas fault ; SHF, trough (Figure 3) . The uplift is 20 miles long, up to four miles Superstition Hills fault ; SJF, San Jacinto fault; She, Superstition Mountain fault wide, and rises to maximum elevations of 1600 to 1700 feet ?4v 70 SHCMA Stvc NO- 9.3d (ingLtutcraac and y .iatni;cr t)r.irilto C_engtuntil[[ ., (Pleist ..xerw)- The hli.»sae= + lrni•c rtai .niJ tea lonnau.ms cha[ untCllue the F`slm -"t .,a. k a ., . aa ._se .u .a few .r,uli anuuutn ut tin1 •w'rOn,rn an4 suuthcrn potuns of the fnJs. licks, bud are run rccognrable on the sase(1„tr J ta. The sttxrhi ucm two-thud of the Indio l-fii'a .art cut by the sub- lxuailld Moss n Creek and t4snn[ng milt-Slip taults . These faults uicgte s.wtheastwar4 ati the .'.mr nt.arieron of the San Arxkcas fault and firm the -umathurstein k,..nasrp rJ rh .. tn .Ls flute T.5 t6 . norrhwtu . one or both of the Running and Mrsx% n Creek faiths met a with the San Arndrea, fault- but the relationship rs nor clear . The B.inoing and Mini in Creek faults arc h.rth z.t»•C faults with ntiinCtOus hesttrr ;t Carthtj i .tkrs . The MrwLion Creek fault p .t.e. through the town of Desert Hot Springs and strikes sotitheastw,trJ through the valley (or six miles to the northwestern end of ;he Intui t hills. For three unites s utheast of Figure 2 . An idealized right-slip wrench fault in map view showing Dcrcn Hot Springs the norrlieasre:rn side of the fault us marked by a structural elements that are cutnawnty ai ociateJ with such a wrench , row of low hills of older alluviuin that are rrun: .ucd on their fault system (scorn Christie-Stick and Biddle . 1985) . southwestern 'flanks by latest faarlt reas`pi . These fault-controlled hills air trisvious on the l_zri st rn>_,gc (tic Figure 3) &< thcart fr .on the An altuwal valley t asst the Lank San bcrnardsrw k4otrtstains to the rnxthca,t, whack emm of Crystalline built:. The laJiw culls xrc' boc*tred on 4 scatshwest by Ccoehclh Valley tha is bet devektntd into hottsuve tracts, resorts_, golf edict s. end agriculture. The Landsat Thematic Mapper data shown in Figure 3 depict irrigated vtgeration sod palm crags as a dark sigrucuze- expuscd cocks as pr:7 tunes. and s.o1,id pawn sand with . sparse ninth vegetation (tid a he& Wit, t ) ai .4 RL* Indio Hills cormsts of Ptsa- Pleisuxene nonmartrie ctaste strata that went depos[tcd span .a basement of granite, rocks (Cretaceous) and associated crystalline rocks- These rocks are exposed in the Little San Betnardino Motantains and arc the source of rite gr nick and mttatttcrphic Jerri:uts in the Nc+ ene strata. The riJgc.anJ- slope sopog aphy of the lndw Hifl~ it a ,isrs.iet nt Air si igsrre 3 . Un4sr Thematic Mapper . of the India Fills Qiroia. Large black atrows nark the Pbtxc Paten Spring three majasr right-slip faults that cut the uplift : from southwest nssetheast. Banniss;,, Mission Creek . and fonnatuxt (Sabins . 1967). This indio faults . Small blur arrows depict right-slip offset of canon, along the strike-slip faults . and open arrows eongasts With the ttnifonin Point to where the xrzike-slip faults act as bartiecs to eroonJwatcc flow- ch . Edom Hill : dhs. Desert Hot slopes Formed by the Springs ; tpc, Thousand Palms Canyon. tmat es were processed at C'he -run Oil Field Research Company, U equivalent Canebrake Habra. California . I , fault symenz. The NW"O H44 he he tw 5 n the CiiehcUa VaScy a" Orocupia AmzataifttM lAunv wts processed at Un" Retwaft SaVOK La6w*uwy, Bpm, Cjkkwn,, Crtck fglor rwvhcs4cfn ,rZ;r, -t . r}: . The tljr&flr.j1 L-Aill ttrtk-Cl C4AW40 449V the twcchem W-ftift *f IK51 th, ir-I oIfT,,rkr .J.1w :; .,ii Gwi 1fr-1 Pa,, av.-J ---, r v,!, ,Whcl,-arj across the northem end A VIV, W k- r a "- , -p--i AW MR nN dthe , w!K- T6 wd VAn , in wo !! : : .[C A 0 w wh d y A do 410 MUS *-lXlthC2$l fTOM the tndw IMI& Agatua trays , . the n .x:}rt .a .hTI qj , Jcl- h igh b have shtfttd along the w-w.. F :%, mix:~ ruthtcai AFThows" 16 .`.;--n Qmk fault cut, Kgw2q Ah-sh he 010 i U"i Wn zmv" Q R~ 3 mv .:-J fit'.--= Creek faults taerge and offsets rhc smahwcg .A"vmg anwT , s. ;Ja lhu wn , wkv "mleowmj a"y the arils.* hl as she W Anckw (auk_ Pare 71 "The trace of the Banning fault is marked by a conspicuous linear tonal anomaly on the Landsat image (see Figure 3) . The northeastern side of the fault has an anomalous dark lijanagure with patches of irrigated vegetation and same housing developments. To the southwest, the tone changes abruptly to the light-colored signature that is characteristic of the. windblown sand that covers much of the northern Coachella Valley . Housing developments and irrigated vegetation are lacking in drta basitxr rcgtvn . Tire senraakubly slurp linear contact between these contrasting Landsar signatures extends northwest along the Banning fault for f4tir miles where it is concealed beneath windblown sand . The following explanation for this Landsat anomaly is based on field observations here and at similar anomalies along other faults in the region . In the northern Coachella Valley. the Banning fault is a barrier to the southward flow of groundwater. Along the northeastern side of the fault the water table i> shallow which supports phreatophytes such as tamarisk, mesquite . and creosote bushes . This vegetation blocks the eastward migration of .oindblown sand; eh .rcFar~, tl, . t.rrn .n .,n chi northeast side of the fault is a caanbinatiun of bare soil and phreatophytes with scattered houses and patches of. irrigated vegetation .
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