Geomorphology o f a :F o r t:ton of the East e rn.most Ventura Basin by Eu gene M. Shoemaker 1 948 Relief model of the HtUJi.phreys ( uadr&.ngl e, view lool\:ing northe <~ st (model and photograph by John Lnnce}. Abstract The hl..UYiphreys ;{uadrangl e is a p o rtion of the eastern­ ; most Ventura Basin underlain by a thic k series of Tertiary sedime ntary rocks . On t~eso rocks a gr eat variety of geomorphic forms have bee n molded by t he p rocess es of r unninc water t y:o ical of· a semi-arid climate ancl. b y several ty:qe s of :rw.ss movement . Among t he dii'ferent c a t ar;o:r> i e s of n1s.ss mo v ement -o:i:' e sent, t:t n evr t ype, the sil t f'l..£:2: ,,._ras obs r-i rvc d . 'T'b.e r::eomor::;hj_c f orm.s o:f s:oecia1 int er•e s t :ore ,s-":'nt i .n thG c:~ ·n ·'.' C\ r !.1.:r~ :) .0 :;. r e rock .;ones, open can:y-onh e ads, as~!rmne tri c cs.nyons , e.nd s tre8In terraces and stra.ths . 'l'he author urges t h e a doption of the definition of strath as thRt :p ai~t o f a n old dissectec~. v alley floor, i ncluding the floors of tributary valleys, which was not part of t h e floodp l a i n of t he main v.all ey strearn. An old erosion surface, the Puc k et·~ Kesa Surface:: , is '?.-,, -.'< p re s e nt in t he Hu..m.nh rey. s I '.~ua dran p:... l e ,:1h.ic-:rr· is corre lHti ve vd,th c 0rtain of the o lde1'"' streain t e rraces . By c o rrc:Jla ting the varis.t i on of .rrad ient a nd of f ill of the stream t e 1'"'r nc e s J-/ with post- 1.ii s consin cliJn2..tic f l uctuati ons ~ the a .~·e of t he :f ucl:e t t i.·~e sa Su rface is s e t a t approximately 600 0 B . c. This correla tion s ets t he p rob&ble ace of the older Ranch o Le. Bl'"' e a deposits 8.t 6 000 to 8000 B. C. and the p :C'obable age of the Car~)8nteria brea deposits at 1 000 to 1 B . C . Contents Introduction. • • • • • • • • 1 • 1 Top o g r aphy • . • o • • • • • • • Geolog ic ~etting . • • • 2 Influenc~ of t he Jrcs ent f 1imate on t h e iro sional /roce sse s • • • 3 Geomorphic Y, rocesse s. • • • • • • 6 General / s pects o f trosion • • • • • 6 '.'J ea t he ring . • • .. • • • • .. • • • • 6 Th e l elati v e 1f ase of l rosi on in t he Te rtiary Y'orma tions 7 ,-~ - ~ I • • • • • • • • • • L>;;1i?.!-? ,I'. i ' 8 Degr8.da tion a l f r ocesses. • • • • • • • • • .. • _\ ,~}' ,/•>I ,; {)1i''. c#'14·- '.I'he Net ion o f Al.mnj_ng '/!at e r 8 ,,.,/"~ : • • • • • • • Llass ]foveme nt • • • • • • • • • • • • • • • 9 Aggradation - The Fact ors Controlling A5gradation by ~~ unni ng 'ii a.t e r • • • • • • • • • • • • • • . 1 7 Cl imatic Flu c t uation. • • • • • • • • ..17 Eeander i n g [>..nd Shi fting o f Eajor St r eo.ms ••1 9 L ass Eovement • • • • • • • • • . 22 •1';. ggr 2. d o.tion Du e t o Reduction of b ast er Strec:rn1 Drain a ge b y Capture o f t h e Catcbrnent B8.sin • • • • • • • • . 22 Stream Cap ture • • • • • • • • • • • • • • • .23 Capture Cau sed by Diffnr ence in Strc8.m 0'7. Load. • • • • • • • • • • • • • • Jo.-J c..) ·.6 9r-::· :.-::2.p ture .Lrom Diff'erenc e in Base Level • • .~ o r.:: apture from Di fference in St rea.rn Leng th. 24 Captur e b y Landsliding . • • • • • • • • " . 24: Capture by Monoclinal Shifting. • • • • .25 Ot her F actors Gove ring the Sha.pe of t be Land Porms. .. • • • • • • • .26 Structure • • • • • • • • • • • .. • • .26 ~ ejuvenation. • • • • • • • • • • • • . 27 Ge omorphic F orms. • • • • • • • • • • • • • • • • . 28 Hock Cones • • • • • • • • • • • • • • .28 Open Ca nyon Heads. • • • • • • • • • • • • • .30 Puckett Mesa - An Op en Canyon Head. • .30 I·1~ iniatur e Op en Ca nyon Heads • • • • • • 33 As-ywmetri c Canyons and Shifting Stre 1.=m1s. • • . 34 Stream Terraces a n d Rel a.ted Erosion Surfa c es .35 Types of Surfaces and Terraces. • • • • .35 Nature and Distribution, Sources, and Economic Value of the Strath and Terr2ce Deposits. • • • • • • • • • • . 42 Correl ation of the Terra ces and Rel a t ed Surfa c e s. • • • • • • • • • • .46 Causes of Rejuvenation and Terrace Formation • • • • • • • • • • • • • • . 57 Geomorph ic Ei s tory o f the Humphreys Ciuadrangl e and t he Surrounding Re s ion • • • • • • • 61 Illustra tions Helie f m.ocle l of t h e Hump hrey s Sluadr a n gle. .Fr ontispiece I P i gurc 1. F1... e sh l a ndslid e • • • • • • • • • • • • • .11 ? igure 2. Deta il of Landslide • • • • • • • • .11 F i gure 3 . Concomita nt slide • • • • • • • • .. • • • .11 ?'i g,ure 4. Si l tflow . • • • • • • • • • • • • • • • . 15 Fi gur e 5. Alluvial cone in Plum Canyon. • • • • .21 F'igure 6. Flum Ca ny on • • • • • • • • • • • • • • . 21 Figure 7 . Alluvia l cone i n I'!iint Canyon. • • • • • • .29 li' i gure 8. Rock cone • • • • • • • • • • • ~ . 29 ? i gure 9. Puck ett Mesa, looking south • • • • • • • .31 i.<' i p;ure 1 0 . Puckett r!ie sa as s e en f'rom the air. • • • .31 F i gu re 11. P anorarnic view of the Sa nta Cla r o. :R i ve1" v alle y • • .. • • • • • • • • • • • • • . 36 li' i cur e 1 2 . 'i'an l-~ Le v e l Surfa c e b e nch • • • • • • • • . 52 / .i:''i r-:ure 1 3 . Terra c e s, strath s, a nd l a ndsl:tde s in t h e • • • • • • • • • • • • . 52 1 L onp:i. t u cl~ ina. 1 t_ r o1~ 1. -.Le on_v er l o .i.,,.,....,,ne '.1. ... S t-.'L""'"' am of .1.v u_cl.<.. e tt hiesa. • • • • • • • • • • • • • • • • • • • Plate I I / Comp ositi on of' the San ta Cla r e.<. Terra c e Gravels .Pl a t e II / I 'l'he Que.t e rna r y JJe ~) O S i ts of the v/e ste rnmo s t Tvvo Thirds of the Eu.mp hr e~• s ;hu a dr ~m gl e , Cal iforni a • • Fl a t e III 're rra c e cSorre l a tion ,£'lap • • • • • • • • • • • . Plate IV • • • • • • • • • • • Pl a t e V Reconstructed Contou r bo.p of the Puckett Ii·! e s a .'.3urfa ce • • • • • • • • • • . l'l a te VI 1 Introduction The area discusse d in this r eport occupies t h e we stern.most two thirds of t he Humphreys ;6u adr a ngle, a s:tx and one- lrnlf minute quadrangl e of' t he Los .Angeles County s eri e s l y ing just nort h of the 34°24 1 parallel 7 ,• 0 ./ and east of t he 118 30 1 me ridian. It covers 25 square miles a n d is readily a cce ssible b y t wo highways from Los Angel e s, one in Bouquet Can yon, and t he other in h int Canyon. Since the top o graphic surveying n as done wit h considerable accura c y , and in fine de tail, it p roved p r actical to do the field mapping on an o z alid cop y of' the published. to:)o gr aphic map enl arged from t h e scale of 1 /2400 to t he s cal e of 1/1200 . Topography Although the n1aximum relief of the area is onl y 1100 feet; t h e s l opes are , in many p l a c e s, exces sive~y steep, especially in the well devel oped badlana.s po:etj_ ons~/ The elevation, i n senRra l decreases from north t o south, t he h i ghest hills, unde:elain b y shists, b e ing [ioca te;g on t he extreme nor•tbern edge o f t he quadrangle. The region i s a portion of' tbe e a.sternmost Ventura b a sin and i s drained 8 by the we stwaPd flowi ng .S anta Cl8.ra Hi ver and its tr-i b u - tar ie s, the southwe st1'ra1"'d f'lowing strea.rn.s in Has kell, Bouquet, and l'Eint Cany ons. Three minor ca.nyons branch of':L /Vl..,a_,._,,..,,_.,J.Af I ., to the east from Bouquet Canyon, <Which are j. from north to 2 I s out h , Texas, Vasqu ez, and Plum fan yons. Ge ologic Setting / 9 An amaz inc; thickne s s of dominantly nonmarine 'J~er ti ary i/ s e d i ments underlies t he entire q_u adrane;l e v1i t h the ezc eption / 0 of t he ex treme northern edge. The formations ~-ecrease in a geJ/1.rom nortb) t~ !\~out h, the general d irection of dip , . /" lt!!,,.() and are usually separated by la~ angula r u n conformity·. Overl y ing t he pre-Cretaceous Felona sch ists are the mode r- ) "!,/"'' a tel y indurated , c ourse , angular beds of the Vasquez s e r ies - \1/ 3 of Oligocene ( ?) ~ge. Above t h is are t h e p oorly consolidated 1 silts, sands, and grav els of t he 'fick Canyon and IHnt Can- yon f ormations , of Lower and Upper Miocene age, respective l y , a p ortior( of t h e Ei n t Canyon for mation bein g l acust1..