STATE OF CALIFORNIA EARL WARREN. Governor DEPARTMENT OF NATURAL RESOURCES WARREN T. HANNUM. Director DIVISION OF MINES FERRY BUILDING. SAN FRANCISCO 11 OLAF P. JENKINS, Chief N FRANCISCO SPECIAL REPORT 33 SEPTEMBER 1953 GEOLOGY OF THE GRIFFITH PARK AREA LOS ANGELES COUNTY, CALIFORNIA By GEORGE J. NEUERBURG Price 5(ty Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://archive.org/details/geologyofgriffit33neue GEOLOGY OF THE GRIFFITH PARK AREA, LOS ANGELES COUNTY, CALIFORNIA By George J. Neuerburg * OUTLINE OF REPORT Page ABSTRACT 3 INTRODUCTION 4 IGNEOUS AND METAMORPHIC ROCKS 5 Metamorphic rocks 8 Pedogenesis 9 Plutonic igneous rocks 9 Vermont quartz diorite 10 Lar quartz diorite _ u Feliz granodiorite _ 12 Hypabyssal and extrusive igneous rocks 14 Geologic history _ 15 SEDIMENTARY ROCKS ~ 16 Cretaceous (?) rocks _ ig Griffith lieds _ ig Cahuenga beds _ 19 Tertiary rocks _ 20 Topanga formation _ 20 Hollycrest formation _ 2,3 Modelo formation 24 Quaternary alluvium _ 24 STRUCTURE \ 24 Faults _ 24 Folds ~ 26 GEOMORPHOLOGY "___ ~_ 27 GEOLOGIC HISTORY 27 ECONOMIC GEOLOGY 28 Quarries _ og Mines 28 Hollywood Lake 28 Engineering geology 28 REFERENCES _.___~ ~ 2 g List of Illustrations Geologic map and structure sections of the Santa Monica Mountains east of Cahuenga Pass and Dark Canyon In pocket Index map showing part of the Santa Monica Moun- tains 4 Major fault blocks of the Griffith Park area of the eastern Santa Monica Mountains 8 Sequence of crystallization in the consanguineous granitic rocks and in the associated dike rocks in the Griffith Park area 9 The nature of the contact zone of the Vermont pluton with the metamorphosed basic igneous rocks__ 10 Photo of discoidal biotite aggregates in the foliated part of the Lar pluton 12 The contact of the Felfz and Vermont plutons and associated metamorphosed basic igneous rocks 13 Schematic diagram of the 'web and inclusion' struc- ture _ 13 Photo showing protomylonite structure along some of the faults in the Feliz pluton 13 Hyopthetical structural relations of the two groups of basement rocks in the Santa Monica Mountains 16 Columnar sections of the fault blocks of the Griffith Park area _ 17 Generalized topography and geology of the Griffith Park area in middle Miocene 21 Photo of fragments of a shell limestone bed in intru- sive basalt _ 21 Photo of basaltic graywacke of the middle member of the Topanga formation 22 Department of Geology, University of California, Los Angeles Con- aensation of a report submitted in partial fulfillment of the requirements for the degree Bachelor of Arts, including also later work. Manuscript submitted for publication June 1951 Plate 1. Pigure 1. Figure 2. Pigure 3. figure 4. figure 5. figure 6. "igure 7. 'igure 8. 'igure 9. igure 10. 'igure 11. "sure 12. igure 13. Figure 14. Photo of a filled river channel in granodiorite 22 Figure 15. Photo of fault scarp and tunnel in fault gouge along the Tunnel fault 26 ABSTRACT The area mapped in the Santa Monica Mountains is bounded on the south by Hollywood, on the north by the San Fernando Valley, on the west by Cahuenga Pass and Dark Canyon, and on the east by the Los Angeles River. Griffith Park is included within the eastern half of the area. The principal topographic feature of the area is an east-west ridge. Cahuenga Peak (altitude 1821 feet) is near the western end of the ridge, and Mount Hollywood (altitude 1652 feet) is just south of the central part of the ridge. The ridge is in line with the crest of the Santa Monica Mountains, but they are separated by Cahuenga Pass, a low transverse saddle. The range is asym- metric, with the steeper slope on the north side. The principal conclusion of this study is that the area east of Cahuenga Pass is a discordant structural and stratigraphic element in the Santa Monica Mountains. The basement rocks and the basement structure in Forest Lawn, east of the Los Angeles River, are like those in the Santa Monica Mountains west of Cahuenga Pass, but are displaced about 6 miles to the north. The Los Angeles River fault is hypothesized to explain these relations. The basement rocks in Griffith Park are exposed in four areas, separated from one another by major faults. The age of the base- ment rocks is not known, but they are probably older than Upper Cretaceous. The stratigraphic position of these rocks relative to the basement rocks west of Cahuenga Pass and in Forest Lawn is not known. The largest area of crystalline rocks is in the south- east quarter of the area, where the oldest rocks are metamorphosed gabbro, diabase, and basalt. These rocks were intruded and meta- morphosed by the Vermont quartz diorite; stoping was the probable mechanism of intrusion. A swarm of aplite dikes, related to the quartz diorite, is intrusive into the contact zone. The Vermont quartz diorite is intruded by the Feliz granodiorite, a massive igneous rock, which ranges in composition from quartz diorite to quartz monzonlte. The irregular, granulated and slickensided con- tact with the Vermont quartz diorite plutonic body and with the metamorphic rock complex is interpreted as meaning intrusion by a nearly solid crystal-charged magma. A fault block of foliated quartz diorite— Lar pluton — is exposed in the northeastern part of the area. The foliation, which is mainly due to aligned, disc-shaped aggregates of biotite, is probably a primary magmatic flow structure. Numerous irregular dikes of malchite and of basalt are intrusive into the Lar quartz diorite. There is a small fault block of granodiorite microbreccia near the western end of this exposure. A larger area of quartz diorite microbreccia is exposed in the central part of the area, and is intruded bj an andesite porphyry dike. These plutonic rocks are questionably correlated with the Feliz granodiorite and Lar quartz diorite, respectively. The sequence of crystallization, the simple mineralogy, the very slight deuteric alterations, the textural and compositional char- acters of the minerals, and the pleochroism and the odd habit of biotite crystals are the same in all of the plutonic igneous rocks. This observation is the basis for suggesting that these igneous rocks are consanguineous and derived from a common parent magma. The suggested sequence of intrusion is Vermont quartz diorite, Lar quartz diorite, and Feliz granodiorite. The indurated sedimentary rocks are of Cretaceous (?) and of Miocene age ; terrace deposits and alluvium are of Quartenary age. The major units are 1) the Griffith beds (Cretaceous ?) ; 2) the Cahuenga beds (Cretaceous ?) ; 3) the Topanga formation (middle Miocene) ; 4) the Hollycrest formation (middle Miocene) ; and 5) the Modelo formation (upper Miocene). The Griffith beds, the Cahuenga beds, and the Hollycrest formations are defined in this report. An isolated fault block contains the Griffith beds — sandstone and fanglomcrate — which may be the oldest sedimentary unit in (3) Special Report 33 the area. The Cahuenga beds are composed of reworked quartz diorite microbreeeia, sandy boulder conglomerate with a thick lens of conglomeratic sandstone, and a well-bedded, coarse conglom- eratic sandstone. The Cahuenga is separated from the overlying Topanga formation by a marked angular unconformity. The Topanga formation consists of three members, separated by unconformities. The lowest member is interbedded arkose, acidic and basic tuffs, basalt agglomerate, basalt breccia, basalt flows, and many irregular intrusions of basalt. It is unconformably over- lain by the middle member of interbedded pebble conglomerate, sandstone, and shale, all composed mainly of basaltic detritus. In view of the unusual composition and the typical graywacke texture, these rocks are called basaltic graywacke. The middle member is missing west of the Brush Canyon fault. The upper member of the Topanga formation is arkose and conglomeratic arkose, with a few thin beds of acidic tuff and thin-bedded siltstone. A single massive basalt sill is present in one place along the base of this member. The Hollycrest formation consists of thin-bedded silty clay shales interbedded with medium-grained arkose. On the north side of Griffith Park, this formation has a thick basal member of sandy boulder conglomerate. In Cahuenga Pass the shale and sandstone unconformably overlie the upper member of the Topanga formation. East of the Cahuenga fault the Hollycrest rests uncomformably on the conglomerate of the Cahuenga beds and on the lower member of the Topanga formation. The Modelo formation is found only in the eastern part of the area where it lies unconformably on the Feliz granodiorte and on the conglomerate of the Hollycrest formation. The rocks are tan to brown organic clay shale and arkose, w T ith thin limestone beds. They contain abundant fragments of wood. Terrace deposits are on the southern and eastern flanks of the mountains and along the sides of canyons. They consist of the rock types which crop out in the vicinity, and are poorly indurated. Faults are the major structural feature of this area ; five major faults separate the area into six fault blocks. The fault block pattern has exerted a major influence on the stratigraphic evolution of the area. The north-trending Cahuenga block on the west side of the area is defined by the Cahuenga and Brush Canyon faults. Vertical movement along these faults is probably greater than 7,000 feet. The Griffith block bounds the north side of the Cahuenga block. The minimum vertical throw on the boundary faults of the Griffith block is probably about 5,000 feet. The microbreccias and the greatest thicknesses of sediments are exposed in these two blocks. The Ferndell block, on the southeast corner of the Cahuenga block, is bounded by the Brush Canyon and Ferndell faults ; it contains most of the intrusive basalt in the area, and probably was one of the major volcanic centers in the Santa Monica Moun- tains. The Riverside block, the northernmost in the area, and the Mount Hollywood block, in the southeast quarter of the area, contain most of the plutonic rocks. Three groups of fold axes are present in the area. The oldest — in the Griffith formation — is unrelated to the fault block structure, whereas the others clearly reflect the pattern of fault blocks. Quarries for road metal and concrete aggregate were the only successful mining activity in this area ; they are now abandoned. INTRODUCTION Location. The eastern end of the Santa Monica Moun- tains is a discordant topographic and geologic block that is separated from the rest of the Santa Monica Mountains by Cahuenga Pass and the Cahuenga fault. The stratig- raphy, structure, and geologic history of the rocks that are older than upper Miocene are different from the stratigraphy, structure, and geologic history of the rocks in the rest of the Santa Monica Mountains. The area that is described in this report is shown on the index map. It is in the parts of the Burbank and the Glendale quadrangles that are bounded approx- imately by longitudes 118°16 / and 118°20' west, and by latitudes 34°06' and 34°10' north. About 15 square mile's are mapped. The area is bounded on the west, from south to north, by Highland Ave., by Cahuenga Pass, and by Dark Canyon (Barham Blvd.) ; on the north and east, Figure 1. Index map showing the part of the Santa Monica Mou tains described in this report. by the Los Angeles River ; and on the south, from wej to east, by Hollywood Blvd., by Western Ave., and l| Los Feliz Blvd. The area is within the Los Angeles Cil limits. Hollywood is on the south side, Glendale on t) east side, and Burbank and Universal City on the nor 1 side of the area. Geography. An east-west ridge, in line with the maj crest of the Santa Monica Mountains, is the princip topographic feature of the area. Cahuenga Pass, a lc gap, separates this ridge from the main crest of the San Monica Mountains. The highest point on the ridge Cahuenga Peak (altitude 1821 ft.) ; the highest point Cahuenga Pass is 714 feet. Mount Hollywood (altitm 1652 ft.) is on a ridge extending south from the ma ridge, about a third of the distance from the Los Angel River to Cahuenga Pass. The range is asymmetric, beir steeper on the north. The Santa Monica Mountains tern nate abruptly on the east against the Los Angeles Rive 1 which has a nearly north-south course along this end the mountain range. Altitudes range from 375 feet Highland Ave. and Hollywood Blvd. to 1821 feet Cahuenga Peak. Canyons on the south flank trend from north to sont On the north flank, the largest canyons trend east-wei Geology of Griffith Park Area, Los Angeles County nd the smaller canyons trend north-south. Canyons are ,eeper and narrower on the south flank of the ridge than o the north. An alluvial fan flanks the southern edge f the area; in some places, the upper part of this fan i eroded. The Los Angeles River is pushed against the janta Monica Mountains on the north side and on the [ist end by the large alluvial fan of the Verdugo Hills narrow alluvial fan, derived from the Santa Monica lountams, lies between the Los Angeles River and the anta Monica Mountains. The climate is Mediterranean. Rainfall is concentrated h the winter months. The south flank of the ridge faces award, and most of the rain falls on the seaward slope he streams are intermittent, and they are dry in early in late summer, depending on the total amount of onfall. The soils are generally thin, but they are fertile most places and they support a thick growth of chap- ral. ^ Use. Griffith Park, the largest municipal park in the )rld, occupies the eastern half of the area. Col. G. J nffith gave the park to Los Angeles City in 1898 Part Brush Canyon, on the west side of the park, was added the park after World War II. Numerous picnic sites ills, and roads were built in Griffith Park by the • P. A. in the 1930 's. Griffith Observatory was built in 32 and 1933. The park contains a municipal golf course oo, and a Greek theatre. Hollywood Lake is a reservoir that belongs to the Los lgeles Department of Water and Power. The reservoir part of the Owens River water system of Los Angeles ty. Concrete aggregate and road metal were quarried in o places in Brush Canyon between 1913 and 1929 e Mexicans are rumored to have had a gold mine in s area; they did mine and calcine a small amount caicite. An abandoned copper prospect is present in ush Canyon. The Don Lee Broadcasting system has a television tion on the next peak east from Cahuenga Peak ; this ik is called "Mt. Lee" (alt. ca. 1700 ft.). The quarry the east side of Brush Canyon is used for stock scenery Westerns by moving picture companies. Forest Lawn netery recently acquired part of Rancho Providencia— part that includes the large valley on the north side this area. The southern foothills are a heavily settled urb of Hollywood. iccessibility. The area is easily accessible, as numer- trails and roads traverse much of it. An excellent work of roads surrounds the area. The Observatory, Greek theatre, and the zoo are served by public trans- tation. Ixcept for the settled parts of the area, exposures are •e numerous and the rocks are fresher in this area a they are in any other part of the eastern Santa nca Mountains. Areas of basalt, sandstone, and shale port a thick cover of brush. Most of these rocks are he parts of the area having the greatest number of is and trails. Conglomerate and granitic rocks have in soil cover, which supports a thin, stunted growth haparral. leld Work and Acknowledgments. Most of the map- ' was done during the spring and summer of 1945, * -,Sn b ! Sement r0cks were ma PP«l during the summer ot 1949. Approximately 70 days were spent in the field Ihe map was drawn on U. S. G. S. quadrangle maps that were photographically enlarged from a 1:24 000 to a 1 :12,000 scale. The work done in 1945 was used for a senior problem in geology at the University of California Los Angeles. Acknowledgment is made to the following people for their help: James Gilluly, Cordell Durrell, Joseph Mur- doch W. P- Popenoe, W. P. Woodring, W. T. Rothwell, Jr., Thane McCulloh, and John DeGrosse. Permission to enter the property of the Don Lee Broad- casting System and of Hollywood Lake was freely given by the owners. Previous Work. The geology of the Santa Monica Mountains has not been investigated in great detail The most complete earlier work is that of Hoots (1931) on the Santa Monica Mountains east of Topanga Canyon Later, in 1932 he published a brief resume of his earlier work in the 15th guidebook of the 16th International Geological Congress. Hoots (1931) gives an excellent resume of the geologic work in the Santa Monica Moun- tains before 1931. Except for a short note on the mineral occurrences of the eastern Santa Monica Mountains (Neuerburg, 1951a, p. 156), later publications do not refer to the Griffith Park area. Students at the University of California have mapped much of the eastern Santa Monica Mountains J B Klecker (ca. 1935) mapped Griffith Park for a senior problem at the University of California, Los Angeles. noJJ\ Anh , eier ' Rod ^ er Hay ward, and L. Grumbine (1935) made a model from Klecker 's map. This model is displayed in the Griffith Observatory Information on the detailed geology of the Santa Monica Mountains west of Cahuenga Pass was obtained noA^^t (1 n? 31) ' the K A " theses of Ja <* G. Elam (1948), John T. McGill (1948), John N. Truex (1950) t N ' T ff eni *g (1951), and George C. Hazenbush (1950), and from the author's Ph. D. thesis on the base- ment rocks west of Cahuenga Pass (1951) ; the informa- nS^ l e f LaWn is taken from A - W - Stepper's report (19ol) and from the author's observations. IGNEOUS AND METAMORPHIC ROCKS ^ B rf e T" t ™ cks are P resent in five of the fault blocks of the Griffith Park area (pi. 1). They are unconformably overlain by sediments of Cretaceous ( ? ) , middle and upper Miocene, and Quaternary ages. Two exposures of base- ment rocks are in fault contact with the sediments and are not overlain by sediments. A very small part of the detritus m the sedimentary rocks is derived from these basement rocks. The basement rocks are metamorphosed basic igneous rocks, biotite quartz diorites, and biotite granodiorite. For convenience, each of the granitic rocks is named. The granitic rocks are consanguineous, and are dissimilar to the biotite-hornblende quartz diorities of the Nichols pluton (Neuerburg 1951c) west of Cahuenga Pass and in Forest Lawn. At least four periods of plutonic intrusion are represented. 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The Vermont quartz diorite is intruded by the Feliz granodiorite, which contains in- clusions of an older quartz diorite that is different from the Vermont quartz diorite and is possibly part of the Lar quartz diorite. The Topanga formation overlies these rocks on the western side. The Hollycrest and Modelo for- mations overlie the igneous rocks on the eastern side. Basalt dikes in the igneous rocks are abundant in a few places. The Lar quartz diorite is the only rock unit in the River- side block (pi. 1 ) ; it consists of interdigitating sheets of foliated biotite quartz diorite, massive biotite quartz diorite and sheared quartz diorite. This quartz diorite is intruded by thin dikes of basalt and by numerous dikes of malchite. The Riverside block contains no pre-Quater- narv sedimentary rocks. A small fault block of Feliz (?) biotite granodiorite microbreccia is present in the Griffith block, near its west- ern end Lar ( ?) biotite quartz diorite microbreccia is ex- posed in the Cahuenga Peak block, and is intruded and metamorphosed by a few dikelets of quartz diorite aplite A dike of pre-Cretaceous andesite porphyry and dikes of Miocene basalt are intrusive into the Lar (?) breccia. Cretaceous ( ?) breccia of the Cahuenga beds unconform- ably overlies and is derived from the Lar ( ?) breccia. Metamorphic Rocks The oldest rocks in this area are metamorphosed gabbi and olivine gabbro. The metagabbro contains dikes metadiabase and of metabasalt. These rocks are present one or two roof pendants and as inclusions in the Vermon quartz diorite. Metagabbro. Outcrops of metagabbro are deep weathered, dark bluish gray to black, much fractured, ar veined bv carbonate. Dark greenish black, fresh nodnl; occur in the weathered rock. The texture of the met. gabbro is blastoxenomorphic, coarse-grained, and ineqij granular. All exposures of the rock are massive. The composition of the metagabbro is not uniform; tj unmetamorphosed rocks probably ranged from elm pyroxene gabbro to clinopyroxene-hypersthene-ohvii gabbro. Thick tabular, euhedral to subhedral crystals plagioclase range in composition from labradonte to bj townite. Slight albitization of the cores of some crysta and replacement by amphiboles in some specimens are tl only alterations of plagioclase. Amphiboles are the principal mafic constituents of tj metagabbro. The amphiboles are secondary and repj sent the principal metamorphic change in the metagabbi'. They consist of common green hornblende, brown horh Geology op Griffith Park Area, Los Angeles County •jlende, blue-green hornblende, anthophyllite, tremolite, Hid actinolite. Zonal relations are common. The amphi- Ifies are replaced by a small amount of clinochlore and otite. Relics of hypersthene and of olivine in these nphiboles have been partly or completely replaced by jirbonate, by chalcedony, and by veinlets of bowlingite. Metadiabase. Metadiabase occurs as irregular masses fault contact with all other rocks, as inclusions in the ermont quartz diorite, and as dikes in the metagabbro. lost outcrops are weathered ; both fresh and weathered ecimens are dark gray to black. J The texture is blastodiabasic, fine to medium-grained; e finer grained varieties are blastoporphyritic. The only xtural changes are those resulting from the recrystalli- Ition of the ferromagnesian minerals to amphibole, lorite, biotite, and epidote. The composition is 50-55 percent plagioclase, 30-40 per- jnt hornblende, 1-5 percent biotite, 10 percent chlorite, j) percent quartz, and 0-2 percent epidote. Plagioclase feges in composition from labradorite to bytownite; i erations are slight and consist of replaeement'by albite,' j-icite, and a fibrous zeolite along cleavage cracks. In ^ne specimens, hornblende is partly replaced by tremo- \i. Epidote and biotite replaced amphiboles and they are hlaced by penninite. Apatite is the only accessory min- il. Metabasalt. Irregular dikes of metabasalt are common i, metadiabase and in metagabbro. The Vermont quartz rite contains many fragments of metabasalt, The fathered and the fresh rock are almost black; most ex- jsures are fresh. Weathered specimens are friable and i.tain numerous carbonate veinlets. The former igneous texture is well preserved; it was : phyritic to seriate with an intergranular groundmass. •■w structure in the groundmass is shown by the crude tallelism of tabular plagioclase crystals and by the ' -ping of the fabric around phenocry'sts. In outcrop, the ' icture appears to be massive. j'he composition is 55-60 percent andesine-labradorite, percent hornblende, 15 percent biotite, and 0-5 percent jrtz. Granules of opaque iron minerals and euhedral :^tals of apatite and zircon are present in small : >unts. Phenocrysts of plagioclase comprise 5 percent of ! rock. I he principal metamorphic changes were recrystalliza- of ferromagnesian minerals to small granules and my prisms of common green hornblende, and to poiki- jastic biotite crystals; the plagioclase crystals are un- bred. The optical properties of biotite crystals are ptly like those of the biotite crystals in the Vermont i rtz diorite ; the biotite may have been introduced from 1 Vermont magma during metamorphism. '• agenesis ! etamorphism of the basic rocks in this area is confined lydrothermal alteration of mafic minerals, in the com- i absence of shearing stress. Addition of volatile sub- *ces, principally water, is postulated to explain the '■ ystallization of low grade amphiboles from former \ xenes and olivine. The specimens of metabasalt that "included in the Vermont quartz diorite differ from |r specimens of metabasalt only by having larger i Bits of biotite and hornblende. This seems most rea- Taole 2. Mineralogic compositions of the plutonic igneous rocks in Griffith Park. The insignificant amounts of minor accessory in in cm Is and of alteration products are not included. Estimated percentage of mineral constituents Plagio- clase Micro- cline Quartz Biotite Horn- blende Rocks of the Vermont pluton Chilled border part 60-75 55-80 5-35 50 50 55 20 65 50 30-60 25 45 0-1 35-60 10 40 tr 0-2 10-25 35 25 10-20 5-30 30 30 40 40 35 20 35 25-40 39 25 5 5-15 5 9 10 5 1 15 10-15 5-10 1 5 0-2 tr-5 Main part . Aplite & pegmatite Rocks of the Lar pluton Massive pait 1 Foliated part.. Sheared part.. Alaskite 4 Inclusions in Feliz pluton Microbreccia Rocks of the Feliz pluton All parts . Aplite . Microbreccia. sonably explained by the assumption that a small amount of water, iron, and potash have been introduced from the Vermont magma. Plutonic Igneous Rocks The Vermont and Lar quartz diorites and the Feliz granodiorite are three separate intrusions, which with their associated dikes, two areas of microbreccia, and the inclusions of quartz diorite in the Feliz granodiorite form a closely related group. Except for small variations in the actual amounts of the minerals, all the igneous rocks have these same characteristics: 1) all of the min- erals have the same minor, non-specific properties; 2) an unusual sequence of crystallization — especially the PRIMARY SECONDARY WEATHERING Magnetite - - Hornblende Zircon — Apatite - Plagioclase Allanite ~1 Biotite Quartz Microcline Epidote L Penninite Sericite Albite Sphene Pyrite Clay Limonite Carbonate 1 L Figure 3. Sequence of crystallization in the consanguineous granitic rocks and in the associated dike rocks in the Griffith Park area. Special Report 33 late position of biotite; 3) biotite has a space-filling habit; and 4) very slight deuteric alteration. The rocks of the Lar and Feiiz intrusions contain high percentages of quartz that correspond to silica percentages that are equal to or greater than those in most granites (Daly, 1933, table 1) ; no evidence whatsoever suggests a replace- ment — or introduced— origin for any part of the quartz content in these rocks. Such mineralogic and textural similarity implies consanguinity, probably best explained by the hypothesis that these rocks crystallized serially from magmas derived from a common source. The primary minerals of the igneous rocks are plagio- clase, microcline, quartz, biotite, hornblende, allanite- epidote, monazite, magnetite, zircon, and apatite. The secondary minerals, products of deuteric alteration and of weathering, are magnetite, myrmekite, clinozoisite- epidote, garnet, penninite, sericite, albite, sphene, pyrite, clay, limonite, and carbonate. ' *r *. *. *. *. *. '. ' 1 '^*^'. *. *. *. *♦ *• ' »l#iliiMM^s--^ . *& \ \ \ \J> *. *, \ C~)\ \ *, *. *, V. *, *. '. '. *. ^ *• *. *. *. *• '• *• *• *- * '• ^ *, \ , *^ 1 -H Metobasolt Metodiobose Vermont pluton (quartz diorite) I Main part Chilled border on apophyses Metaqabbro Chilled border part Figure 4. The nature of the contact zone of the Vermont pluton and metamorphosed basic igneous rocks. Composite sketch from roadcuts along Griffith Park Road, Mt. Hollywood block, Griffith Park. Vermont Quartz Diorite The Vermont pluton,* which is composed of quartz diorite, is intrusive into the metamorphosed gabbro-dia- base-basalt complex that comprises the faulted remnants of a roof pendant in the central part of the Mount Holly- wood block. The pluton consists of two homogeneous tex- tural parts, a medium-grained part — called the main part • Pluton is a term, coming into more general use, which includes vari- ous bodies of igneous rock formed by slow cooling, particularly where the form of the rock body is irregular or unknown. Ed. note. — and a fine-grained chilled border part. The main pari contains inclusions of the chilled border part. Dikes ol, aplite and pegmatite are common in the pluton and irj the metamorphic rocks. The contact between the metamorphic rocks and th< Vermont pluton is a wide zone that is divisible into a zone of apophyses and a zone of inclusions. The chillec border part of the Vermont pluton is a discontinuou: mass around the roof pendant. The chilled border ancj the metamorphic rocks on the periphery of the pendan are veined by irregular apophyses of quartz diorite tha range in width from an eighth of an inch to several feet 1 A chilled border, as much as 2 inches thick, is found alonj. the sides of these apophyses. The zone of apophyses passes insensibly into a zon of inclusions that comprise the remainder of the exposes part of the Vermont pluton. The size and abundance o inclusions decreases away from the roof pendant ; numei, ous inclusions, averaging one foot in diameter, are present in all of the exposures of the pluton. Most of the inclvJ sions are fragments of the chilled border, but a few frag ments of the metamorphic rocks are also included. Th ( quartz diorite shows no textural changes in the vicinit of the inclusions. A few fragments of the included chille: border rock are metamorphosed. Petrography. In most exposures the chilled horde rock is fresh, light gray, and fractured. Where weathered the rock is friable and almost black. Most of the chillei border is massive. In places, flow structures are presen due either to 1) parallel discoid aggregates of biotitj crystals, or 2) subparallel tabular plagioclase crystal The texture is uniformly hypautomorphic, fine-graine< and e<|uigranular. The ferromagnesian minerals in tl metamorphosed specimens are xenoblastic and poikiL blastic. Mineralogically, the chilled border part is like tH main part of the pluton. The metamorphosed speeimei of the chilled border rock contain more hornblende (5 pej cent ) and biotite (10 percent). The additional biotite an hornblende may have been introduced by the enclosb magma. The other minerals of the rock are unchanged. The main part of the pluton forms the north side j the Mount Hollywood block. Most exposures are weat: ered light rust-brown; each grain of the rock is coate with a thin film of limonite. The fresh rock is dark gra and usually fractured; the fractures are coated wij limonite. The structure appears to be massive in outcro]' an ill-defined flow structure is visible on polished surface! and is due to a crude parallelism of discoidal aggregate of unoriented biotite crystals. The texture is hypaut| morphic, equigranular, and medium-grained. Along t| borders of apophyses and in places along the thick chilled border part, the main part grades into the chillij border within less than an inch. Aplite and Pegmatite Dikes. Aplite and pegmati; dikes are numerous in the contact zone and in the met morphic rocks. Such dikes are common in the centr part of the pluton. Most of the dikes are aplite; a f* small granite pegmatite dikes are present. The dikes are light cream-colored. The rock is fan- resistant to weathering, and crops out above the click- ing rocks. Most of the aplite dikes are sheared along tl borders, and, to a lesser extent, within the bodies of tt dikes. Geology op Griffith Park Area, Los Angeles County 11 The texture is fine-grained xenomorphic, inequigranu- lar; pegmatites are coarse-grained and have a xeno- morphic texture with patches, of graphic texture The composition ranges from quartz monzonite aplite to granite aplite. fetrogenesis. Intrusion of the Vermont pluton appar- ntly was in two stages. The first is represented bv a thick dulled border on the periphery of the roof pendant of metamorphic rocks. No evidence exists as to the mode of intrusion during the first stage; the presence of mag- batic currents during this stage is indicated by the flow structures in some specimens of the earlier chilled border 'ocks. The second stage of intrusion is represented by the ransgression of the earlier chilled border. Flow struc- ures indicate the existence of magmatic currents during Ins stage also. The following features are excellent evi- dence that the second stage of intrusion was by means if stoping : 1 ) veining of the metamorphic rocks and of i he earlier chilled border rocks by apophyses; 2) blocks sf wall-rock that are nearly pried loose; and 3) the hnmlance of inclusions. No evidence of chemical assimilation is present Inclu- ioiis have knife-sharp contacts with the quartz diorite nd the mineralogy and texture of the inclusions show o relation to the contact with the quartz diorite Further- lore, most of the inclusions differ in no wise from the ame rocks where present in the roof pendant The thin chilled borders on the apophyses of the second tage of intrusion and the lack of a chilled border of uartz diorite around inclusions demonstrate that the mntry rock during the second stage of the intrusion ad a temperature only slightly less than that of the hagma. On the other hand, the thick chilled border of ie first stage of intrusion reflects a large temperature ifference between the wallrocks and the magma The •Klence for a higher temperature of the country rock urmg the second stage of intrusion gives reason to sug- 'St that the greater part of the metamorphic changes the basic igneous rocks happened during this stage of trusion. ° ir Quartz Diorite The Lar pluton, composed of quartz diorite, is exposed the Riverside block (pi. 1), where it is intruded by alchite and by basalt dikes. Inclusions of quartz diorite the Feliz pluton in the Mount Hollywood block and the iartz diorite microbreccia in the Cahuenga Peak block i.v be parts of the Lar pluton. petrography. Most outcrops of this quartz diorite are eply weathered and white. Three textural varieties of n#r P i° n are ma PP ed in the Riverside block- 1) a •II tohated quartz diorite (foliated part), characterized biotite aggregates ; 2) a poorly foliated to massive, even a line to medium-grained quartz diorite (massive ; and 3) an even-textured, well-foliated rock leared part) that contains zones of mylonite and micro- tia parallel to the foliation. The contacts between the foliated and massive parts ' sradational in distances of 1 to 6 inches. The struc- ■al relations of these parts, both on large and on small | ie, consist of interfingering sheets of quartz diorite In ■ees, the foliation is swirled. The texture of the foliated part is xenomorphic- hypautomorphic. Ragged tabular oligoclase crystals are poorly oriented with their broad faces subparallel to the plane of foliation. The foliation is primarily a reflection of disc-shaped aggregates and bands of biotite ; the biotite crystals of these aggregates do not have a preferred orientation. The texture of the massive variety of quartz diorite is hypautomorphic-xenomorphic. Biotite crystals are evenly distributed. The gradation between the two parts consists of a rapid decrease in the proportion of biotite that is aggregated. The texture of the sheared part is xenomorphic- oriented ; ragged tabular oligoclase crystals and irregular anhedral elongated quartz grains and groups of quartz grains show a marked parallelism. Most, but not all, biotite crystals are also oriented; the crystals show a space-filling habit in part ; some crystals are bent. Rocks of this part do not contain biotite aggregates. Thin zones of mylonite and thick zones of microbreccia, which contain sheared inclusions are present. These zones are common- est along the south edge of the Riverside block. By de- crease in perfection of mineral shape-orientation and by lessening of the intensity of fracture, the sheared part grades into the other parts. The sheared part is hydro- thermally altered, with the extensive development of chlorite, epidote, and sericite. Inclusions. Inclusions are rare in the Lar pluton. Two mmeralogic varieties are present, The texture of both types is granoblastic and poikiloblastic. Melanocratic in- clusions are composed of 15 percent hornblende, 20 per- cent biotite, 20 percent quartz, and 45 percent plagioclase. Leucocratic inclusions contain 25 percent microcline, 20 percent plagioclase, 30 percent quartz, 20 percent biotite, and 5 percent hornblende. All inclusions are disc-shaped and are parallel to the flow structure of the pluton. Associated Bikes. A few short, thin alaskite dikes are present along planes of- foliation on the north side of the Riverside block. They have a xenomorphic, coarse- and fine-grained texture. Fragments of white, fine-grained, xenomorphic meta- aphte are present in a few places in microbreccia zones in the sheared part. The rock consists of thin bands of partly recrystallized microbreccia and of protomylonite. The composition is 60 percent quartz, 30 percent clino- zoisite, 9 percent zoisite, and 1 percent penninite. Quartz Diorite Inclusions in the Feliz Pluton. These inclusions are correlated with the Lar quartz diorite, be- cause of the similarity of the mineral composition and of the texture of the two rocks. These inclusions, like the Lar pluton, are intermediate in composition between the other two intrusives. The inclusions range from a few inches up to 500 feet or more in diameter. They are scattered throughout the Feliz pluton, and are more abundant than is indicated on the geologic map (pi. 1). The contact between the inclu- sions and the Feliz pluton are sharp. The outlines of the inclusions are jagged and irregular ; they appear to have been controlled by joints in the quartz diorite inclusions. The structure of the inclusions is massive, and the texture is hypautomorphic, equigranular, and fine-grained. A few thin zones of microbreccia are present. 12 Special Report 33 Microbreccia of Lar(f) Quartz Diorite. The micro- breccia in the Cahuenga Peak block is correlated with the Lar pluton for the same reasons that the quartz diorite inclusions in the Feliz pluton are correlated with the Lar pluton. The rock is a coarse-grained macrobreccia, with num- erous intersecting zones of microbreccia. The breccia is traversed bv subparallel planes of gouge, along which the breccia has' been chloritized. These shear zones are later than the brecciation ; they offset aplite dikelets that in- truded and metamorphosed the breccia. The quartz diorite in the northern half of the exposure is more intensely brecciated and finer grained than that in the southern half of the exposure. The hypautomorphic, equigranular, and fine-grained texture of the quartz diorite is well preserved in small fragments. The minerals are only slightly altered, hardly more so than in the non-brecciated igneous rocks in this area. Fragments of vein quartz are present in a few places. A few small thin dikelets of quartz diorite aplite are intrusive into the microbreccia. No evidence of their origin is available. The dikelets are surrounded by thin aureoles of altered breccia. The aplite is hypautomorphic, equi- granular, and fine to medium-grained. Plagioclase, 50 per- cent of the rock, is altered to sericite and albite. Quartz (35 percent), biotite (replaced by chlorite, 10 percent), and hornblende (pseudomorphosed by carbonate, 5 per- cent) comprise the rest of the rock. Adjacent to the dikelets, the microbreccia is replaced by feathery aggregates of phengite( ?) and by irregular patches and veinlets of carbonate. Plagioclase is albitized, and quartz is partly replaced by phengite(?). Phen- gite( ?) comprises the rest of the rock (40 percent). The original cataclastic texture is almost obliterated. Origin of Foliation. Two kinds of foliation are present in the Lar pluton. The zones of brecciation and mylonite are a kind of foliation that is the result of shearing of a solid rock. This cataclasis may have happened shortly after crystallization of the magma and before the rock had completely cooled. This is suggested by 1) parallelism of the zones of cataclasis with foliation of the quartz diorite ; 2) the extent of the hydrothermal alteration, which is much more intense than that of the microbreccias else- where in this area; and 3) the texture of the sheared part of the pluton. The foliation of the foliated part and the much poorer foliation of the massive part probably is the result of laminar flow during intrusion, as suggested by the follow- ing observations : 1) Disc-shaped aggregates of biotite, but not single crystals, have a preferred orientation. If due to shearing of a solid rock, the biotite crystals should be oriented. 2) In places the foliation is swirled. 3) Tabular oligoclase crystals are parallel. 4) The contacts between the foliated and the massive parts are gradational and the two parts have irregular, interfingering contacts. Small, discoidal schlieren of the foliated quartz diorite are enclosed in and parallel the poor foliation of the massive part. 5) Inclusions and alaskite dikes parallel the foliation. Mode of Intrusion. The structure of the Lar pluton and its differences in composition can be explained as the result of serial injections of magma closely spaced in time. Each successive injection took place before the preceding injection had completely crystallized. If differ- entiation was taking place during the period of intrusion, the order of intrusion would be 1) massive part, 2) foliated part, and 3) sheared part, assuming intrusion to be in the order of decreasing alkali-content. This sequence is also indicated by the finer grain of the massive rock relative to the other parts, assuming the finer grain to be indicative of chilling, as in the Vermont pluton. Continuation of stress conditions in the sheared part during and after final crystallization may have produced the zones of brecciation and mylonitization. The con- centration of the effects of shearing in the southern part of the exposure gives reason to suggest an origin of the Griffith block in the stress pattern that caused the folia- tion of the Lar pluton, in the Riverside block. The con- tact between the Lar pluton and the Vermont pluton, under the sediments in the Griffith block, may have been a wide fault zone in its final stages of development, end- ing up as the Griffith block. Feliz Granodiorite The Feliz pluton, which is composed of granodioritk rocks, is exposed in Griffith Park in the Mount Hollywooc block (pi. 1) and for a short distance in the foothills south of Los Feliz Blvd., where it is buried under Ter tiary sediments. The granodiorite microbreccia in th< Griffith block is probably part of the Feliz pluton. Th< Feliz pluton appears to be intrusive into the Vermon pluton and into the metamorphic rocks. -* 1 J 4fc #->', *?v .-»: .% i3f ve Figure 5. Discoidal biotite aggregates in the foliated part of the Li biotite quartz diorite. Natural size. Photo by John Be Grossc, 19$ The contact of the Feliz pluton with the Vermoi pluton and with the metamorphic rocks is exceeding! irregular in detail, but in general, it is a fairly straigr line (pi. 1). Along the contact, rocks of the Feliz plutc. and the older rocks are brecciated ; shear zones in tl older rocks are subparallel to the contact. No textur or mineralogic changes, related to the contact, are preset in the granodiorite or in the older rocks. Petrography. Outcrops of the Feliz granodiorite a deeply weathered, friable, and white; fresh rock w Geology op Griffith Park Area, Los Angeles County Vermont Pluton (quartz diorite) + + + Fehz Pluton (granodionte ) Aplite Chilled border Metadiabase Main part ■» » Microbrecc ia sure 6 The contact of the Feliz and Vermont plutons and asso- ted metamorphosed basic igneous rocks. Sketch from roadcut along Vista del Valle Drive, Mt. Hollywood block, Griffith Park. and in only one place. The structure is massive The cture is hypautomorphic-monzonitic, equigranular and e to medium-grained. The intrusive is heterogeneous- ge, vaguely outlined, subrounded masses — having imeters on the order of hundreds of feet to hundreds of rds— of a finer grained variety are enclosed in a thick re 7. Schematic diagram of the 'web and inclusion' structure n by variations in the grain size and in the mineralogic compo- sition of the Feliz granodiorite. 13 web of a coarse-grained variety (figure 7) The varia- tion m grain size appears to show a spatial relation to the quartz diorite inclusions, but not to the contact with the older rocks; that contact transgresses the web-struc- ture of the Feliz pluton. The amount of microcline shows a close relation to grain size; it is most abundant in the coarser grained parts. The rocks of the pluton range from biotite quartz diorite to biotite quartz monzonite ; the mean composition or the pluton seems to be that of a biotite granodiorite. Along pre-Miocene faults, the granodiorite is sheared into alternating bands of mylonite and protomylonite in zones ranging from half an inch to 30 feet in thickness bhckensides and mullion structure are spectacularly de- < Figure 8. Protomylonite structure along some of the faults in the Feliz granodiorite. A few small inclusions of mafic rock are present in half a dozen places in the pluton. They have a granoblastic texture and consist chiefly of biotite and hornblende Presumably they are fragments of the older metamorphic rocks. Aplite Dikes. A very few, small, irregular dikes of aphte are present in the Feliz pluton ; they are derived probably from the magma from which the Feliz pluton crystallized. The texture varies irregularly from xeno- morphic to hypautomorphic, inequigranular, and from fine to medium-grained. The dikes are quartz monzonite aplite. Microbreccia of Feliz (?) Granodiorite. A small fault block of hydrothermally altered granodiorite micro- breccia is exposed in the western end of the Griffith block No evidence exists to prove that this rock is present under the sediments throughout the extent of the Griffith block, but such an assumption seems reasonable. The rock is deeply weathered in all exposures, and is light greenish-white. Thin, intersecting zones of micro- breccia and of mylonite traverse this microbreccia The zones have no preferred orientation. The texture is cata- clastic; a few aggregates of broken grains suggest a former monzonitic texture. One small, white aplite dike was found in this breccia. It consists of alternating bands of microbreccia and of protomylonite. The minerals are 45 percent plagioclase (albitized), 50 percent quartz, 3-4 percent orthoclase and a small amount of epidote. Small stringers of ortho- clase form a cement for the other minerals of the rock Special Report 33 Mode of Emplacement. The presence of large inclu- is of quartz diorite (Lar ?) in the Feliz pluton in the ;nt Hollywood block gives reason to suggest that the mode of intrusion in this block, at least in part, was by stoping. Intrusion of part of the pluton may have local- ized along the Griffith block, and subsequently brecciated and subjected to hydrothermal alteration. The contact of the Feliz pluton with the Vermont pluton and its roof pendant of metamorphic rocks has the following unusual characteristics. 1) The overall contact is a relatively straight line. 2) In detail, the contact is an irregular, sutured boundary. 3) A zone of granulation is present on both sides of the contact, but the granulation is more intense in the granodiorite. 4) Shear planes are confined to the older rocks. 5) The older rocks show no metamorphic changes that might have resulted from intrusion of the Feliz pluton. 6) The compositional and textural variations in the Feliz pluton show no relation to the contact. 7) Structures of the rock masses on both sides of the contact are truncated along the contact. 8) The contact is parallel to the foliation in the Lar pluton, and to the trend of the Griffith block. (This is the regional strike of the basement rock structures of the Santa Monica Moun- tains and of the surrounding mountains of the Transverse Ranges.) The contact shows features both of fault and of intru- sive contacts. Possibly it is a fault contact formed when the granodiorite was nearly, but not wholly, crystalline. The lack of metamorphic effects attributable to the grano- diorite magma suggests that the rock was relatively cold at the time of intrusion. The lack of shear planes in the granodiorite and the granulation that gradually disap- pears a few feet from the contact are the basis for sug- gesting a partly fluid magma at the time the contact was formed ; had it been solid, shearing analogous to that in the older rocks might be expected. Drag by such a viscous magma along the cold, older rocks may have been the mechanism — i.e., plucking — that caused the suturing of the contact. Fragments of the older rocks should be present in the granodiorite, if the suggestion is correct, but they were not found. The magma may have been too nearly solid to readily incorporate such frag- ments or they may have been removed from the region of the fault that is now exposed. Crystallization and Differentiation. The web struc- ture of the pluton is an unusual feature, whose explana- tion may be as follows. Large inclusions of cold wallrock (quartz diorite), on being incorporated in the magma, caused the surrounding magma to begin to crystallize sooner and more rapidly than the magma that was free of inclusions. After the inclusions had been sufficiently warmed and after crystallization had progressed suffi- ciently far to determine the final texture and mineral composition of the adjacent magma, some of the inclus- ions may have risen or have sunk in the magma and thus have produced the present partly irrational distribution of the inclusions. The earlier and more rapid crystalliza- tion of magma surrounding the inclusions should have caused a concentration of plagioclase relative to micro- cline — the last mineral to crystallize — and a finer grained texture ; the coarser grained parts of the pluton have a higher microcline content than the finer grained parts. That such a pronounced influence by these inclusions is possible seems reasonable in view of their large mass. Hypabyssal and Extrusive Igneous Rocks Numerous dikes, sills, irregular shallow intrusive bodies, flows, agglomerates, breccias, and tuffs are pres- ent in the Griffith Park area. The rock types are, in order of abundance, augite basalt, olivine basalt, malchite, alkali trachyte tuff, and andesite porphyry. The malchite and the andesite porphyry are pre-Cretaceous intrusives. The basaltic rocks comprise perhaps the greatest bulk of the lower member of the middle Miocene Topanga forma- tion in this area. A single dike of andesite porphyry is present in the quartz diorite microbreccia in Brush Canyon. Malchite dikes are confined to the Riverside block in this area, but are common in the basement rocks of the Santa Monies Mountains west of Cahuenga Pass. Basalt dikes are mosl abundant in the western end of the Riverside block and ir the eastern end of the Mount Hollywood block. A fev basalt dikes are present in the quartz diorite microbreccn in Brush Canyon. Sills and irregular intrusives of basal and extrusive basaltic rocks are most abundant in thi Ferndell anel Mount Hollywood blocks and in the Ca huenga Pass block. A few small sills of basalt are intru sive into the other sedimentary rock units in the Griffitl Park area. Malchite. Numerous malchite dikes are intrusive int< the Lar pluton in the Riverside block ; they are presen nowhere else in this area. The dikes are strikingly simila to the pre-Cretaceous malchite dikes west of Cahueng Pass (Neuerburg, 1951c). Because of a similarity of un usual petrologic characteristics, as well as a similai restricted occurrence to basement rocks, the malchite i: the Riverside block is considered to be also of pre-Creta ceous age. The dikes range in thickness from 1 foot to 30 feet. Th rocks are massive. Textures range from very fine-grainee felted in chilled borders and in thin dikes through panai tomorphic to porphyritic-panautomorphic. Fresh spec mens are dark bluish gray; weathered rocks are cream white. Phenocrysts consist of augite and andesine. The essei tial minerals are andesine (typically much altered) an kaersutite (?) (titaniferous hornblende — Campbell an Schenk, 1950, p. 682). Titaniferous magnetite and apatil are the minor accessories. Augite is present in some spec mens. Abundant clinozoisite, chlorite, and carbonate ai space-filling elements in the rock fabric. The very fin* grained varieties of these dike rocks apparently consist e albitized andesine, augite, and intragranular chlorit with some titaniferous magnetite and, in some specimen pyrite. Andesite Porphyry. A small dike of blue-gray anel site porphyry is intrusive into the quartz diorite micr breccia in the Cahuenga Peak block. Fragments of th rock are present in the overlying Cretaceous ( ?) seil mentary breccia and conglomerate (Cahuenga beds). Tl rock consists of white andesine phenocrysts set in a fin grained matrix of felted oligoclase crystals and intr granular elements consisting of apatite, quartz, biotit magnetite, penninite, epidote, anel calcite. Basalt. Dark brown and red-brown intrusive anel e trusive bodies of basalt comprise the major part of tl lower member of the Topanga formation. Extrusi basalt is confined to this member. The exposures of basa Geology of Griffith Park Area, Los Angeles County 15 id sediments in the quarry on the east side of Brush anyon (in the Ferndell block) show well the complex ructure of the basalt and sediments. Apparently deposi- on of sediments and accumulation of pyroclastic basalt ternated and produced interbedded and interfingered nits ; intrusions of basalt occurred repeatedly through- it the entire period of deposition of the lower member : the Topanga formation. An unusual inclusion structure typical of this member in the Ferndell block: frag- ents of sediments, agglomerates, flow breccias, flows, and irlier intrusives comprise a chaotic jumble of inclusions ithin masses of intrusive basalt. This structure is re- lated on a smaller scale in places in the Mount Hollywood ock. The abundant dark brown extrusive basalt consists ostly of coarse-grained agglomerate. A few thin pillow va flows are present in places in the Mount Hollywood ock ; a pillow lava about 50 feet thick occurs near the top the lower member of the Topanga formation in the ihuenga Pass block. No massive flows of basalt were cognized, although such are present on the west side of ihuenga Pass. The extrusive basalt is usually not sicular. All forms of basalt are deeply weathered to a ft, brown, clayey mass. Dikes of basalt in the Feliz pluton have parallel sides. jie structure is massive and chilled borders are present, single large pipe-like intrusive in the easternmost ex- sure of the pluton is surrounded by a swarm of thin ! salt dikes. Elsewhere in the pluton, dikes are uncommon, appears likely that this pipe was a feeder to a volcano. . swarm of highly irregular, thin dikes of dark brown halt are present in the Par pluton in the Riverside lick; the dikes are most numerous in the western end ( the block. The irregular shape is probably due to joints rl fractures in the quartz diorite. Thin dikes of dark I wn basalt, along shear planes, are present in the quartz rite microbreccia in Brush Canyon. 3mall sills of basalt are present in all of the sedimentary f mations. Large sills and irregular intrusive bodies of 1'k brown basalt are common in the lower member of 1 Topanga formation. Many of these intrusives are a ygdaloidal ; the distribution of the amygdules is erratic a I appears to have no relation to contacts or to inclu- s is. Veins of zeolites and related minerals are common ii hese intrusive rocks. The texture ranges from porphy- ftc and intergranular to intergranular ; most specimens ntrusive rock are porphyritic. Phenocrysts generally 1 iprise about 10 percent to 15 percent of the rock ; the n ierals are andesine-labradorite, augite, and in some 8] iimens olivine. The groundmass consists predomi- n tly of andesine with a little augite and magnetite ; el irite and chlorphaeite (?) fill spaces in the ground- K s. Corroded and broken xenocrysts of plagioclase and q rtz occur in a few specimens. he earliest and the most abundant zeolite is analcite. A Dciated minerals are natrolite, heulandite, apophyllite, tl nsonite, calcite, and prehnite. These minerals occur I imygdules, vein fillings, and as selvages along the bi lers of pillow basalts. The central parts of crystals oi ilagioclase in all the specimens of basalt that were e> nined are replaced by jagged patches of analcite and I i little albite. Between one-quarter and one-third of a ' the plagioclase is replaced by analcite. The large 111 ant of analcite in the basalt and in cavities in the basalt suggests an excess of soda in the basaltic magma and lava. Such an excess of soda appears to be a charac- teristic feature of all Tertiary basalt and diabase in the Santa Monica Mountains (C. Durrell, personal commu- nication). More than three-fourths, by volume, of the intrusive basalt in the Santa Monica Mountains, east of Topanga Canyon, is present in the Griffith Park area, and most of that in the Ferndell block. From this single fact, it seems likely that the Ferndell block was a major volcanic center during the middle Miocene. Flow Breccia. Numerous small inclusions and a few "beds" of a distinctive red flow basalt apparently repre- sent a stratigraphic marker in the lower member of the Topanga formation. The rock is resistant to weathering and crops out above the enclosing basalt. It consists of flow breccia, bedded tuff, and scoriaceous flows. The tex- ture is intergranular or intersertal. The groundmass con- sists of dark red, nearly opaque chlorphaeite ( ?) . Angular to subangular fragments of crystals of augite, analcitized and albitized andesine, and basalt are set in this ground- mass. Many of the fragments in the breccia are vesicular ; some of the vesicles in the fragments and in the scoria- ceous flows contain a small amount of analcite, natrolite, and chlorite. Alkali Trachyte Tuff. Beds of alkali trachyte tuff, 10 to 15 feet thick, occur in the lower and upper members of the Topanga formation. Casts of small pelecypods show that the beds were deposited in the sea. The beds in the upper member are light cream tuff and gray, sandy im- pure tuff, interbedded with silty clay shale and arkose ; those in the lower member are inclusions in basalt. The tuff is very fine-grained, massive, and much fractured. Laths of albite-oligoclase are the most abundant compo- nents of the rock. A very few grains of quartz and frag- ments of alkali trachyte comprise the remainder of the rock. Boulders of alkali trachyte are present in the basal conglomerate of the Hollycrest formation. Hoots (1931, p. 101) mentions the occurrence of trachyte dikes of probable middle Miocene age in the western part of the eastern Santa Monica Mountains. It seems likely that the alkali trachyte tuff represents an extrusive facies of the trachyte dikes in the Santa Monica Mountains, west of this area. Similar tuff beds are noted by Terpening (1951) on the west side of Cahuenga Pass. Geologic History Order of Plutonic Intrusion. No unequivocal direct evidence of the sequence of intrusion of the plutonic rpcks of this area is available. The sequence is postulated to be as follows : Vermont pluton, Lar pluton, and Feliz pluton. This sequence is based on two assumptions: 1) the rocks of the three plutons are consanguineous and were derived serially from the same parent magma ; and 2) the spatial relations of the three plutons is essentially the same as it was during the period of intrusion. Aplite dikes are very abundant in the Vermont pluton, whereas they are rare in the other plutons. The aplites of Vermont pluton contain much potash feldspar in strong contrast to the aplites of the other plutons. This distribution is readily explicable if the Vermont pluton 16 Special Report 33 ■20 Gneissose Quartz Diorite -« r N- . .. Spotted_L- panga formation is in the Ferndell block and in the Mom Hollywood block on the south side of the Griffith bloc An appreciable thickness of the Topanga formation present in the Cahuenga Pass block, but this part of tl Topanga formation is the easternmost extension of tl Geology of Griffith Park Area, Los Angeles County 17 •!':'■•: i'j ■':::V.i • . 1 18 Special Report 33 more typical rocks of the Topanga formation west of luenga Pass; the deposition of this part of the forma- tion appears to have been independent of the fault block structure of the Griffith Park area. The conglomeratic member of the Hollycrest formation is present only in the Griffith block ; thus it appears to be the product of local conditions of deposition. The Hollycrest formation, in the Cahuenga Pass and in the Cahuenga Peak blocks, ex- tends westward to Coldwater Canyon (Terpening, 1951 and Truex, 1950), but does not seem to be present else- where in the Santa Monica Mountains. Its deposition appears to have been independent of the fault block struc- ture of the Griffith Park area — except for the basal con- glomerate. Three conglomerate beds are mapped : 1 ) Griffith beds ; 2) Cahuenga beds ; and 3) the lower member of the Holly- crest formation. They are easily separable in the field because of the differing lithology of the boulders con- tained in them. The granitic conglomerate of the Griffith beds contains abundant fragments of metamorphic rocks and of rocks that may be identified with outcrops in the Verdugo Hills, on the north side of San Fernando Valley. The source area of the rock types in the conglomerates of the Cahuenga and Hollycrest formations is not known. These conglomerates contain almost no metamorphic rocks. The granitic conglomerate of the Cahuenga beds has abundant pebbles and cobbles of acid porphyries and boulders of a unique vesicular basalt. The conglomerate of the Hollycrest formation contains principally boulders of various granitic rocks and little else. Cretaceous (?) Rocks The oldest dated sedimentary rocks in the Santa Monica Mountains are Upper Cretaceous in age (W. P. Popenoe, personal communication). Such rocks comprise the so-called Chico formation, which crops out in isolated fault blocks in the Santa Monica Mountains. The Chico formation is largely a granitic boulder conglomerate con- taining abundant pebbles and cobbles of acidic porphy- ries, which serve to distinguish it from other boulder ( onglomerates in the Santa Monica Mountains. Except for the lower member of the Hollycrest formation, no granitic boulder conglomerates, younger than the Cre- taceous, are known in these mountains. Principally for this reason, the Cahuenga beds in the Griffith Park area are assigned to the Cretaceous ; correlation with the Chico formation is not suggested because of differences in de- tailed lithology. For the same reason, the Griffith beds are tentatively assigned to the Cretaceous. Structural evidence indicates that this unit is older than the Cahuenga beds. Two or three boulder conglomerate formations underlie the "Chico" formation in the Santa Monica Mountains west of this area. A red boulder conglomerate, probably a cor- relative of ???, (Terpening, 1951; Truex, 1950), crops out in small patches along the basement contact from Cahuenga Pass to Stone Canyon. In Nichols Canyon (Terpening, 1951) near the Encino Reservoir (Neuer- burg, 1951c), and in Forest Lawn are pre-Chico granitic boulder conglomerates that have been derived almost en- tirely from the underlying basement rocks. None of the Chico and pre-Chico conglomerates seem to be likely lithologic correlatives of the Griffith or of the Cahuenga beds. Unfortunately, the general absence of invertebrate fossils in the pre-Tertiary sediments of the Santa Monica Mountains and the isolated occurrences of the rocks do not lend encouragement to the hope that their stratig- raphy will be elucidated. Fish scales in the Cahuenga i and Griffith beds offer some hope, once the use of fish scales for age determinations of early and pre-Tertiary forms' are adequately documented. Griffith Beds The Griffith beds are exposed in a fault block within and near the eastern end of the Griffith block. The unit is in fault contact with sediments of the Topanga and Holly- crest formations on all sides. On the basis of lithology, the- beds are separable into four units or members not sepa- ( rately mapped because of lack of exposures. The lowest member, about 500 feet thick, consists predominantly of thick-bedded medium-grained arkose with thin beds of silty clay shale, siltstone, and pebble conglomerate. The second member consists of thick beds of cobble conglom- erate and of arkose ; a few thin beds of platy, sandy shale are present. This member is about 150 feet thick. The third and fourth members are not easily separated; both members are composed of boulder conglomerate. The third member has about 20 percent arkose matrix as compared to 30 to 40 percent in the fourth member. The fourth member shows much variation in grain size, whereas the size of the boulders in the third member is more uniform.' The arkose is massive, medium to coarse-grained, and angular to subangular. Small rock fragments are abund- ant. The cement is'calcite. The massive arkose and the arkosic matrix of the conglomerates are weathered to a soft, friable, yellow brown mass ; the fresh rock is greenish gray. Thin-bedded, white to tan silty clay shales are inter- bedded with thin beds of siltstone and of fine and medium- grained arkose. Fish scales are uncommon in the shale they are evidence for calling the two lowest members marine. The boulders are subangular to rounded and have rough surfaces. Boulders 3 and 4 feet in diameter are common ii the fourth member. About 70 percent of the boulders con sist of gray, medium-grained granitic rocks. Also present are boidders of acidic porphyries, basalt, diabase, anortho. site, sandstone, alaskite, quartz diorites (some from tin Vermont pluton), metadiabase, metabasalt, mica schist augen gneiss, banded gneiss, quartzite, hornfels, marble and aplite. The distribution of the different rock types ii the conglomerates of the Griffith beds is not uniform. Meta morphic rocks are most abundant in the third and fourtl members; acidic porphyries predominate in the conglom erate beds in the lowest member; boidders of metamor phosed basic igneous rocks and the associated Verinon quartz diorite are common in the lowest member. Tin other rock types are fairly evenly distributed. Only the boulders from the Vermont pluton and m associated metamorphic rocks could be identified wit! the basement rocks in this area. Many of the other boul ders are similar to rocks exposed in the Verdugo Hill and in the San Gabriel Mountains on the north side o San Fernando Valley. Anorthosite crops out over a larg' area in the San Gabriel Mountains (Miller, 1934). Ai unusual schist containing large porphyroblasts of feld spar is identical, in hand specimen, with a rock exposei in the San Gabriel Mountains, near Olive View Sana Geology op Griffith Park Area, Los Angeles County 19 •ium. The assumption that much of the material in i Griffith beds is derived from the San Gabriel Moun- ns is based on the similarity of these rocks. The texture the third and fourth members is like that of the present uvial fans on the south flank of the San Gabriel Moun- ns. For this reason, it is suggested that the greater rt of the Griffith beds is a fanglomerate. Because of the occurrence of the Griffith beds in an lated fault block, it is impossible to find direct evidence its stratigraphic position in the Griffith Park area, lerefore the term "Griffith beds" is used for conven- it reference without raising this unit to formation itus. The rock types present in the conglomerates are ferent from the rocks in other conglomerates in this ;a; no similar formation crops out elsewhere in the nta Monica Mountains. The southern part of the Grif- i beds is tightly folded ; the fold axes trend east-west, e axes are at an angle to all other axes of deformation the Griffith Park area, and, unlike these other axes, >se folds are unrelated to the fault block structure of s area. The deformation is more intense than in the ier sedimentary formations in this area. The trend the fold axes and the intensity of deformation in the iffith beds are a basis for suggesting that this is the est unmetamorphosed sedimentary rock in the Griffith rk area. iuenga Beds The Cahuenga beds consist of five units or members; pse are 1) a basal sedimentary breccia; 2) a coarse dy boulder conglomerate; 3) a lens of conglomeratic dstone; 4) a sandy pebble conglomerate; and 5) a 1 1-bedded conglomeratic sandstone. Except for the i ilder conglomerate, these rocks are confined to the iuenga Peak block. A small amount of the boulder glomerate is exposed in the southwestern part of the '-. ffith block and in the Ferndell block. The Topanga i nation rests unconformably on the conglomerate in 1 Cahuenga Peak block and in the Ferndell block. A l'k section of Cahuenga beds is missing at the base I he Topanga formation. The Cahuenga beds are folded i» a broad anticline in the Cahuenga Peak block. '■ edimentary Breccia. The sedimentary breccia crops on barren slopes or on slopes with a thin cover of that supports a sparse chaparral cover. The rock is sive ; it consists of poorly rounded and angular frag- its. The largest number of fragments consist of quartz ite microbreccia and of blue andesite porphyry de- d from the underlying microbreccia and andesite. A well rounded pebbles of fine-grained quartz diorite quartzite are present in the breccia. The fragments •an ion, but not abundant. The weathered rock is brown, fii e, and contains no cement. The fresh rock is bluish rcf and is cemented by calcite. In every place that it is ; I ed, a 1- to 2-foot layer of fault gouge is present Figure 12. Fragments of a shell limestone bed in intrusive basalt. Griffith Park Road. Photo by John Be Grosse, 1950. along the contact between the arkose or the basalt and the underlying basement rocks. A discontinuous 4-foot bed of shell limestone is present in the central part of the lower member. On the east side of the Ferndell fault, the shell limestone rests unconform- ably on intrusive and extrusive basalt and on arkose. In the western part of the Ferndell block it occurs as inclu- sions in intrusive basalt. The rock is very resistant to weathering and forms bold though small outcrops above the surrounding basalt. It is composed of oriented and distorted shells of oysters ; a few distorted foraminifera are present. The rock analyzes 97 percent calcium car- bonate ; foreign material consists of fragments of crystals of hornblende, orthoclase, quartz, biotite, augite, analcite, zircon, and apatite. Numerous veinlets of calcite traverse the rock ; the shell fragments are only slightly recrystal- lized. Contacts with intrusive basalt and inclusions of shell limestone consist of a pasty mixture of limestone and basalt. Where the lower member of the Topanga formation is relatively undisturbed, the shell limestone appears to com- prise a stratigraphic zone. Also, the brick red basalt flow breccia appears to comprise another stratigraphic zone about 50 feet above the shell limestone. The deposits of arkose and the accumulations of basalt below the strati- graphic horizons defined by the limestone and the flow breccia thicken very rapidly to the west and southwest into the Ferndell block and to the north of the main ridge in this area. The lowest arkose bed increases in thickness from a knife-edge to 100 feet under Mount Hollywood to about 1,000 feet at the southern end of the Ferndell block. This suggests that the Ferndell block was a rapidly sink- ing trough during the formation of the lower member of the Topanga formation. Further reason for believing that the Ferndell block was a mobile trough during the depo- sition of these rocks is the concentration of intrusive ba- salt in the northern part of this block ; intrusive basalt is not common either in the southern part of the block or in the Cahuenga Peak and in the Cahuenga Pass blocks. The area of most intrusive basalt is close to the exposure of the Special Report 33 rtz diorite microbreccia, which therefore may have channeled the intrusion in the Ferndell block. The occurrence of discontinuous beds of arkose and shell limestone that are interbedded with extrusive basalt and that are not inclusions in intrusive basalt suggests that deposition of these rocks was in isolated, small basins or that numerous minor unconformities are present in this member ; probably both hypotheses are true. West of Cahuenga Pass, the lower member of the To- panga formation of the Griffith Park area is underlain by lenticular conglomerates, sandstones, and shales that have a basal white arkose, which is present throughout much of the eastern Santa Monica Mountains (Terpening, 1951 ; Truex, 1950). Middle Member. The middle member is composed of interbedded mudstone, conglomerate, conglomeratic sand- stone, sandstone, and sandy shale. The composition is unusual ; it is a dark chocolate brown, weathered rock, con- taining mostly basaltic detritus. I call this rock basaltic graywacke. Graywacke is probably a misnomer from the standpoint of composition (Petti John, 1949, p. 245), but it is an apt name insofar as texture is concerned. Figure 13. Basaltic graywacke of the middle member of the To- panga formation. Griffith Park Road. Photo by John De Grosse, J950. The formation is ill-sorted for the most part, and it exhibits rapid textural variations from shale to a boulder conglomerate that contains boulders up to 3 feet in dia- meter in places. In a few places, the rock is fairly well bedded, but in general it is poorly bedded to massive. In one exposure a thin flow having pillow structure is present ; this is the only crystalline basalt in this mem- ber. Small angular to subrounded fragments of various types of basalt are set in a matrix of dark brown, opaque, claylike material that has a waxy luster (chlorophaeite ?). Mineral fragments consist of andesine, oligoclase, quartz, and augite, with minor amounts of myrmekite, analcite, biotite, and zircon. The boulders and cobbles consist primarily of augite basalt and olivine basalt, Figure 14. A filled river channel in granodiorite at an elevation i 1,000 feet. Griffith Park Road. Photo hi, John De (}i ossc, 1950. with a few boulders and pebbles of pink granite, quart diorite, quartzite, acidic porphyries, and arkose. Thj arkose is like that in the lower member of the Topangl formation. Large boulders and smaller fragments of tl brick red basalt from the lower member are common i the lower parts of the basaltic graywacke. The unconformity at the base of this member represen considerable erosion : three separated areas of this roc are present in Griffith Park. The area at the souther end of the Ferndell block and the area at the norther end of the block rest unconformably on the lowest be of arkose in the lower member of the Topanga formatio:: The area underlying the main ridge east of the Bru.': Canyon fault rests unconformably on. a bed of brick rt basalt that is several hundred feet above the base of tl lower member at this point. The basaltic graywacke confined to the Mount Hollywood and Ferndell bloci The three exposures, from south to north are respective 1 700 feet thick, 300 feet thick, and 1,400 feet thick. Upper Member. The upper member of the Topan,' formation consists mostly of ill-sorted, coarse-grained co glomeratic arkose. Locally small lenses of medium-grain; arkose and of coarse-grained arkose are present. A fe beds of thin-bedded siltstone, sandy shale, and alki trachyte tuff are present in the conglomeratic arkose. Tj rocks are well indurated and crop out above the und<- lying basaltic rocks of the lower and middle members. Tl weathered rock is light tan to brown ; fresh specimens a; bluish gray. Sorting is poor and the grains are subangul' to subrounded. The mineral fragments are quartz, oli<- clase, albite, orthoclase, biotite, sphene, zircon, apati, and epidote. The pebbles are well rounded and siiioci fragments of acidic and basic porphyries, quartzite, gr«| ite, quartz diorite, basaltic graywacke, scoriaceous bra red flow basalt, and alkali trachyte ( ?). Acidic porphvr< and quartzite are the commonest and most abundant p« bles in the exposures of this member in the Mount Hoi - wood block. Basaltic rocks predominate among the pebb^ in the conglomeratic arkose in the Cahuenga Pass bloc Except for a sill that is intrusive in one place along tfe base of this member, basalt is not present in this nienib • Geology of Griffith Park Area, Los Angeles County 23 ^he upper member has a maximum thickness of 1,000 t in the Mount Hollywood and Ferndell blocks and of i feet in the Cahuenga Pass block. The unconformity he base of this member represents considerable erosion, it rests on the lower member in Cahuenga Pass and on h the lower and middle members in the Mount Holly- )d and Ferndell blocks. A small exposure of conglom- tic arkose, surrounded by alluvium, is present in the tern end of the Griffith block, where it presumably lerlies the Hollycrest formation. ige. The only invertebrate fossils that were found in Griffith Park area are from the Topanga formation. ?se fossils are poorly preserved casts and shells in ose, trachyte tuff, and in shell limestone. The localities m which fossils were collected are shown on the geologic P (pl. 1). Table 3. Fauna of the Topanga formation (middle Miocene).* Upper member 2303 Loner member 2302 2306 2301, nun a ?rtebrata tropoda ulla sp. c incellaria sp. x inns sp. x uritella ocoyana Conrad x cypoda miantis sp. x irdium (Trachycardium) quadrage- narium Conrad c x ementia sp. ? x x ementia (Egesta) pertenuis conra- diana (Anderson) x varicella cf. dentata var. eburnea Reeve x isinia cf. ponderosa Gray x da ochsneri Anderson and Martin c icinisca cf. nuttalli Conrad x Ueonia sp. c trea sp. c x cten sp. x cten cf. andersoni Arnold c cten cf. saneta-ludovici Anderson I and Martin x ropeeten cf. miguelensis Arnold x c .| ropecten crassicardo Conrad c c . ncoides sp. c c c lacoides (Miltha) sanctaecrucis Ar- iiold e c c ' Una sp. x I present ; c = common. fossils are deposited in the collection of the Depart - of Paleontology, University of California, Los Ange- riie locality numbers are those of the University of 'omia, Los Angeles. . P. Ponenoe offers the following comments on the age is fossil assemblage : Of the forms specifically identified in the above list (table the dementia and the I'haeoides occur in both Lower and Idle Miocene faunas in California, but apparently range ler than Middle Miocene; on the other hand, Cardium drigenarinm and Lyropecten craxsicardo are found in both die and Upper Miocene strata, but apparently do not occur he Lower Miocene; the common occurrence of these species, i the added occurrence of Turitella ocoyana thus fixes the of the assemblage very clearly in the Middle Miocene, so- 'd 'Temblor Horizon' of the California Tertiary. The gen- aspect of the compared species in the check list is in full ■I'd with this age assignment. The presence of Diraricella is of interest in suggesting rela- | ships of the fauna with that of the Caribbean. The genus is If known in California only in the Coyote Mountain 'Latrania' formation (Hanna, G. D., 1926, p. 454-455, 464-165, pis. 20, 26) and in the Altamira shale member of the Monterey shale in the Palos Verdes Hills (Woodring, W. P., Bramlette, M. N., and Kew, W. S. W., 1946, p. 28). The Altamira shale is probably slightly younger than the beds carrying Diraricella in the Santa Monica Mountains; the age of the Latrania sand is determined by some authors as Miocene ; by others, as Pliocene." Hollycrest Formation The Hollycrest formation consists of thin-bedded, light brown, medium- and fine-grained arkose and white to gray silty clay shales. The arkose-shale ratio is about 5 : 1. The arkose is well-sorted and has graded bedding. The rock weathers to a soft clayey mass of sand containing numer- ous shale chips. A thick pebble-boulder conglomerate comprises the basal member of this formation in the Griffith block. About 40 percent of the rock is a medium- to coarse- grained subanoular arkose that weathers to a light tan friable mass. The pebbles and boulders are predominantly grandiorite, quartz diorite, pink granite, and diorite. A very small proportion of the boulders are brick-red basalt (from the lower member of the Topanga formation), al- kali trachyte, andesite, dacite, and quartzite. A few, thin, persistent lenses of coarse-grained arkose and sandy clay shale are present in the conglomerate; these lenses are most abundant near the base of the shale. The contact be- tween the sandstone and the conglomerate is conformable and oradational ; thin beds of conglomerate are present in the lower 50 feet of the sandstone. The formation is exposed in the Griffith, in the Cahuenga Peak, and in the Cahuenga Pass blocks. A small sliver of the conglomerate, resting unconformably on the upper member of the Topanga formation is present on the south side of the Griffith fault in the Mount Hollywood block. A small area of the conglomerate rests unconformably on granodiorite and is overlain by the Modelo formation in the northeast corner of the Mount Hollywood block. The conglomeratic member of the Hollycrest formation is con- fined to the Griffith block and to its near vicinity. The base of the sandstone, in the Cahuenga Pass block, is almost conformable with the underlying Topanga formation, but the shale continues east across the Cahuenfra fault zone into the Cahuenga Peak block, where it rests unconformably upon the lower member of the Topanga formation and upon the conglomerate of the Cahuenga formation. Age. The only exposure of a contact between the Hol- lycrest formation and the overlying Modelo formation in this area is in the northeastern corner of the Mount Holly- wood block, where the Modelo formation rests on the Hol- lycrest conglomerate. The nature of this contact is not certain ; it may or may not be a fault, as shown in plate 1. For this reason, the possible significance of this contact must be ignored. West of Cahuenga Pass, the Hollycrest formation is conformably overlain by the Modelo formation and uncon- formably overlies the Topanga formation, locally with an angular discordance of 90°. Near Coldwater Canyon, the lower part of the Modelo formation is middle Miocene (R. Orwig, cited by Terpening, 1951, p. 22). This then fixes the age of the Hollycrest formation as middle Miocene. The Hollycrest formation is lithologically distinct from both the Topanga and Modelo formations. Hoots (1931), Truex (1950), and Terpening (1951) have included it as Special Report 33 member of the Topanga formation, principally because he lack of the characteristic siliceous shales of the Mo- delo formation. However, the formation is conformable with the Modelo and not with the Topanga formation. The name Hollycrest is taken from the highest point in Cahuenga Pass, where the formation is well exposed. Modelo Formation The Modelo formation in the Griffith Park area is con- fined to a crumpled monocline on the east end of the Mount Hollywood block, where it rests unconformably on the Feliz piuton and on a thin sliver of the Hollycrest conglomerate. The lithology is distinct from that of other shales in this area. The formation is predominantly dark gray laminated calcareous organic siltstone and shale, with which a few beds of fine- to medium-grained orange and brown arkose and thin beds and discontinuous lenses of fine-grained orange limestone are interbedded. The rocks weather to a light tan color. Fragments of fish scales, wood, and leaves are abundant in these rocks; the wood fragments are most abundant in the siltstone and shale beds and appear to be absent in the limestone. A zone of gouge, 1 foot to 2 feet thick, is present between and paral- lel to the contact between the Modelo formation and the Feliz granodiorite in every place that it is exposed. The lithology is not typical of the rest of the Modelo formation in the Santa Monica Mountains nor of that in the foothills east of the Los Angeles River; no siliceous sediments are present. Hoots (1931) collected foramini- fera of upper Miocene age in this formation along the west bank of the Los Angeles River a few hundred feet south of Los Feliz Blvd. (Hoots' loe. 9) ; he mapped this occur- rence as "lower Modelo." Quaternary Alluvium Two formations of alluvium are present in stream can- yons and in the alluvial fans that are on the north, south, and east sides of the Griffith Park area. The older alluvium is exposed on the sides of canyons in their lower reaches and in the upper parts of the alluvial fans ; an abandoned stream channel filled with poorly indurated conglomeratic alluvium is exposed at an elevation of 1,000 feet in grano- diorite on the south flank of Mount Hollywood. The older alluvium is eroded. The younger alluvium fills canyon bot- toms and is a thin veneer on the surface of the alluvial fans. The older alluvium is poorly indurated ; the younger alluvium is not indurated. Both formations consist of angular to subangular fragments, up to 10 feet in diam- eter, in an unsorted matrix of sand grains, silt, and clay. No bedding is evident. The fragments in the alluvium are derived from the underlying and surrounding rocks. The texture differs according to the rock types surrounding the alluvium ; in the granitic rocks the alluvium is an unsorted coarse-grained, argillaceous arkose. In areas of sediments, the alluvium consists of a secondary conglom- erate derived from older conglomerates or of a mixture of fragments of all rock types found in the surrounding sediments. The two alluvial formations are probably both Quat- ernary, in view of their lack of induration — a fair criterion in southern California. STRUCTURE The structure of the Griffith Park area is dominated by high angle faults; folding, igneous activity, and sedi- mentation are clearly related to and controlled by the faults. These faults appear to have been active throughout the formation of all of the rocks in the area. The Cahuenga Peak, the Griffith, and the Ferndell blocks are the princi- pal local basins in which the greatest thicknesses of sedi- ments accumulated. The stratigraphy and structure of the area provide evidence of nine periods of major orogenic: activity, and of several periods of minor orogeny. The Griffith Park area is a discordant structural anc stratigraphic element in the eastern Santa Monica Mourn tains. The structure of the eastern Santa Monica Moun tains is succinctly described by Hoots (1931, p. 127) : ". . . forces of uplift recurrently active in the eastern part of i the Santa Monica Mountains from the Jurassic period to the present have resulted in a pronounced, somewhat asymmetrical anticline. During the first periods of deformation . . . uplift was concentrated in the central granite-slate area and produced a fold that plunged rapidly to the west and also to the east. The middle Miocene uplift of the central area appears to have pro- duced several and possibly many major high-angle tension faults along the borders of the active area. . . . Some of these faults were accompanied by intrusions of basalt ... In consequence of these recurrent periods of deformation the Santa Monica anti- cline is no longer a simple fold. Much of it has been disrupted by faults and basalt intrusions, and the southeastern limb of the fold is lost from view . . . covered with alluvium." The basement rocks of the Griffith Park area are diffet cut from and apparently unrelated to the basement rock: west of Cahuenga Pass ; the presence of rocks of th Nichols piuton in Forest Lawn (Neuerburg, 1951c) sug gests that the anticlinal structure of the eastern Sant Monica Mountains may continue east of the Los Angele River, but offset to the north. The major lines of discor tinuity that separate the discordant Griffith Park are! from the normal Santa Monica Mountains structure ar the Cahuenga fault zone and the Los Angeles River faul Faults Most of the faults are not geometrical planes, bi| warped surfaces. These warped surfaces probably are pr, mary, because most of the rocks, where they intersect tl- faults, do not show any deformation that might be attril uted to folding of the fault surfaces. This is surprising inasmuch as no fault, with one exception, has a zone < ; gouge and breccia more than 1 foot thick. The faul probably originated as warped surfaces as a result j refraction in passing from one rock type to another ar, from one structure to another. Such behavior of faults wj well established by Knopf (1929, p. 24) in the Moth-! Lode system of California, where it is possible to measu the index of refraction between slate and greenstoii Major changes in attitude — e. g., the Brush Canyon far — probably resulted in passing from such incompete rock, as brecciated or soft rock, to hard massive compete! rock like the granitic rocks. The major faults in the Griffith Park area that we most important in the structural and stratigraphic evol,- tion of the area are the Cahuenga fault zone, the Brnl Canyon fault, the Ferndell fault, the Griffith fault, tj Hollister fault, and the Los Angeles River fault. T; Cahuenga fault and the Brush Canyon faults define tj Cahuenga Peak block, and the Hollister and the Griffil faults define the Griffith block. These two blocks contait Geology of Griffith Park Area, Los Angeles County 25 ! greatest thickness of sediments in this area; micro- tia may underlie the sediments for the full extent of ;h of these blocks. Jah uenga Peak Block. The Cahuenga fault zone trends rthwest by north along its northern exposed half, where 'orms the contact between the Hollycrest formation and ! Cahuenga beds. This part of the fault is on the south- it side of Dark Canyon where it approximates the line sudden change in slope from the Cahuenga Peak hog- :k to Cahuenga Pass. The southern half of the fault is eries of subparallel, en echelon faults that separate the huenga formation from the Hollycrest formation, and ! Hollycrest formation, where it overlaps the Cahuenga mation, from the Topanga formation. The fault zone [icates that the Cahuenga fault curves to strike approxi- tely north along its southern half. rhe Brush Canyon fault follows the winding Brush nyon on the south slope of the main ridge, where it lerally strikes north. A few hundred feet south of the ge, the fault begins to curve toward the west, and on north side of the main ridge, it strikes approximately 60° W. The strike of the shear planes in the micro- ccia of quartz diorite on the west side of Brush Canyon ws no systematic orientation ; no relation to the Brush lyon fault is apparent. Joth of these faults are offset by numerous faults hav- a few hundred to a thousand feet horizontal movement. 1 displacement along the Cahuenga and Brush Canyon Its is indeterminate. Both faults probably have about same absolute displacement ; the Cahuenga Peak block . sedimentary unit that probably was thrust up as a rle block. In no place is the displacement less than )0 feet. Extrapolation of the structure of the Cahuenga Is in the north part of the block to the surface of the ?ment rock would indicate a displacement on the order ,000 to 8,000 feet. I'hese faults were probably initiated with the breccia- . of the quartz diorite. Later movement occurred be- an the deposition of the Cahuenga beds and Topanga '■ nation, between the deposition of the Topanga and 'lycrest formations, and after deposition of the Holly- i t formation. The last movement probably was not r he direction of movement of the Cahuenga fault and Brush Canyon fault, except for the last movement Big the Cahuenga fault, is not apparent. It is difficult i mceive of the curved trace of the Brush Canyon fault (ing originated other than by vertical movement. The uenga Peak block was a graben during the deposition f he Topanga formation; it has been a horst since the e nning of the deposition of the Hollycrest formation. riffith Block. The Griffith block strikes about N. 60° /'and is situated in the northeast corner of the area. The » ^rn suballuvial extension of this block is probably I cated by the Los Angeles River fault ; the western ex- ■ ion either truncates or is truncated by the Cahuenga It. The block is bounded by the Griffith fault on the ) h side and by the Hollister fault on the north side ; i ;wo faults, the block, the fold axes in the Hollycrest 3 lation in the block, and the foliation and the shear M in the Lar pluton are subparallel and have approxi- i? ly the strike N. 60° W. ; the average dip is between 0,ind 80° NE, although the faults are more nearly ver- tical. The average strike and dip of the Nichols pluton (Neuerburg, 1951c) and the older rocks on the north Hank of the Santa Monica anticline and the foliation and inclu- sions in the granitic rocks northeast of Griffith Park in the San Rafael Hills are about the same as in the Griffith block. This strike and dip would appear to be the regional atti- tude of the basement rocks in these contiguous areas. A number of minor faults offset the Griffith and Hollis- ter faults by a few hundred feet. The trend of the two faults is not a straight line ; only a small part of the irreg- ularities can be attributed to topography. The general direction of dip is to the north, but locally the Hollis- ter fault dips to the south. The Griffith block is a graben except near the eastern end, where a rhomboid horst of the Griffith formation is present. Like the Cahuenga Peak block, the displacement on the boundary faults and the direction of movement are indeterminate. Were the Holly- crest formation the only sedimentary rock in the block, the displacement would be on the order of 1,500 feet, but if it is assumed that a complete section of the Topanga formation and Cahuenga beds and the minimum vertical component of the thickness of the Griffith beds underlie the Hollycrest formation, the minimum vertical displace- ment would be on the order of magnitude of 10,000 feet. The Griffith block appears to have formed as a result of the shearing stresses that caused the foliation in the Lar pluton and that produced the zone of breccia and mylonite in the southern part of the Riverside block. Although, sub- sequently, the Griffith block was an important local trough of deposition, it does not appear to have been a topo- graphic low during the deposition of the Griffith beds. The fold axes in the Griffith beds are the only axes of de- formation in this area that are wholly unrelated to the fault block structure ; the Griffith fault truncates these fold axes. Apparently the Griffith block remained inactive until after the deposition, folding, and perhaps erosion of the Griffith beds, when the block was downdropped to form a structural graben and a topographic trough. The block appears to have been a sinking trough throughout the deposition of the Topanga and Hollycrest formations. This condition probably accounts for the local accumula- tion of a basal conglomerate member in the Hollycrest for- mation. Ferndell Fault. The Perndell fault and the southern part of the Brush Canyon fault appear to define a block on the southwest corner of the Mount Hollywood block that was an important, rapidly sinking trough during deposition of the lower and middle members of the To- panga formation. The thickness of the lower member of the Topanga formation rapidly increases away from the core of granodiorite on the east side of the Ferndell fault into the Ferndell block. Further evidence for the existence of this block as a structural unit is the presence of an over- turned syncline in the Topanga formation that is appar- ently confined to this block. Stratigraphic reasons for suggesting that a fault line scarp was present along the trace of the Ferndell fault at the beginning of deposition of the Topanga formation were given in a previous sec- tion. The Ferndell fault is a hinge fault according to its present outcrop. The southern end of the fault has a mini- mum displacement of 1500 feet. The fault cannot be traced north of the Tunnel fault ; the shell limestone beds are not 26 Special Report 33 offsel oss any inferred continuation of this fault to the north. Two explanations are possible: 1) the fault is a hinge fault with no displacement at the north end where the distortion of faulting would be absorbed by the incom- petent extrusive basalt accumulations in this area; or 2) the Perndell fault is an old fault along which no recurrent movement has occurred and that is accidentally exposed by erosion. The only evidence favoring the first alternative is the truncation of the axis of the overturned syncline in the Ferndell block. This evidence is not conclusive for two reasons that suggest that this syncline is a frame fold con- fined to the Ferndell block. The axis of the syncline paral- lels the axis of the sedimentary-igneous wedge in the Ferndell block. The fold is not reflected in the older sedi- ments on the west side of Brush Canyon, a condition which should prevail were the folding not confined to the Fern- dell block. The second alternative finds confirmation of a sort in three features. A hypothetical, concealed extension of the Ferndell fault on a line curving around to intersect the Brush Canyon fault just north of the point where it is off- set by the Mount Hollywood fault (pi. 1), coincides with the approximate northern limit of the chaotic inclusion structure of the northern half of the Ferndell block. This line is also the axis along which the thickness of the lower member of the Topanga formation abruptly increases, and it probably represents the northernmost limit of the Ca- huenga formation in the Ferndell block. Northeast of this line, the fold axes in the lower member of the Topanga formation trend northeast by east ; south of this line, the fold axes strike about N. 45° W. Furthermore, the differ- ences in stratigraphy along the exposed length of the Ferndell faidt are much too large to be explicable on the basis of the apparent amount of movement shown by the Ferndell fault. These observed and inferred phenomena provide a sound basis for the hypothesized concealed ex- tension of the Ferndell fault to intersect with the Brush Canyon fault, and for considering the Ferndell fault to be a branch of the Brush Canyon fault. Were the second al- ternative true, the displacement along the southern part of the Ferndell fault that involves Topanga rocks has taken place as a result of the folding of the rocks in the Ferndell block, but not as a result of active faulting. Los Angeles River Fault. The existence of the Los Angeles River fault is based largely on the distribution of basement rocks (Neuerburg, 1951b and 1951c). The remarkably uniform trend of the structural planes and intrusive contacts in the Nichols pluton on the north flank of the Santa Monica anticline is assumed to hold true for the southeastward extension of this pluton under the alluvium. If this assumption is true, the presence of the Nichols pluton in Forest Lawn and the presence of spotted slate of the Santa Monica formation in the Seaboard well near the intersection of Figueroa Ave. and San Fernando Blvd. are conclusive evidence of the existence of the Los Angeles River fault. The truncation of the structure of the Griffith Park area along the Los Angeles River and the abrupt ending of the Santa Monica Mountains along this same line, and the failure of appearance of the struc- tures and rocks of the Griffith Park area east of the Los Angeles River are further evidence for the existence of the fault. The position of the fault that is shown on the accom- panying plate is arbitrary; the true position is inde- terminate. The strike of the fault that was chosen is als( arbitrary, but it cannot be much different than the actua strike. It is based on the trend of the topographic line o< truncation of the Santa Monica Mountains, on the positioi of the rock types, and on the fact that the igneous anc metamorphic rocks in the San Rafael Hills are closely similar to the Nichols pluton. Movement on the fault i"i : predominantly horizontal ; it is a left lateral fault wit! a displacement of the order of magnitude of 6 miles. Other Faults. Only a few of the numerous less impor tant faults in the Griffith Park area merit brief mention The Tunnel fault was so named by Klecker (ca. 1935), be cause the tunnel north of the Griffith Observatory wa< driven entirely in the fault gouge of this fault. This is thj only fault in the area with a thick zone of gouge ; the zon, is about 40 feet thick at this point ; elsewhere it is less thai 2 feet thick. The Mount Hollywood fault has no vertical component of direction of movement. The direction of di^ placement of contacts by this fault requires that the mov^ ment was horizontal ; the fault is a left lateral fault. Mu' lion structure and slickensides provide supporting evi dence for this kind of movement. Figure 15. Fault scarp and tunnel in fault gouge along the Tunr fault. Vermont Ave. Photo by John De Grosse, 1950. Folds Three principal axes of folding are present in this are; The oldest of these axes are represented by the tight fob. in the Griffith beds. These folds are the only folds that <: not appear to be related to the fault-block structure this area. Furthermore, the east-west strike of the fo axes is unique among the major folds in the eastern San Monica Mountains. The folding in the Griffith beds confined to the relatively incompetent lower bedded par.; folding is not detectable in the massive upper congloi! erate. The thick, massive fanglomerate forms the northe . limb of the northernmost anticline. The next youngest axis of folding is the northeastwa trending anticlinal axis in the Cahuenga beds in tl Cahuenga Peak block; this axis is also present in tl Mount Hollywood block, north of the Ferndell block. TJj anticline was formed prior to the deposition of the T- panga formation for the lower member of this formatii unconformably overlies the Cahuenga conglomerate i Geology of Griffith Park Area, Los Angeles County 27 ith flanks of the anticline, where the Topanga formation mprises a less tightly folded anticline. Rejuvenation of is anticline after deposition of the Topanga formation mduced an anticline in the Mount Hollywood block in e Topanga formation. As a result of this rejuvenation, e Topanga formation slid down the flanks of the anti- inal core of basement rock to produce a gouge zone along e contact that is mapped as a low angle normal fault ■1.1). The third group of fold axes trends northwestward, lese are closely related to the trends of the major fault >cks that were troughs of deposition. The synclinal fold- g in the Cahuenga Pass block may be partly a result of jvement along the Cahuenga fault zone. The overturned ncline in the Griffith block probably resulted in large rt from the down-faulting of this block. The overturned ncline in the Perndell block reflects the axis of major tokening in the Topanga formation, which roughly rallels the Griffith block. The overturned synclines dip r ay from the center of the area ; for this reason, a north- st-trending anticlinal axis, not reflected in the remain- >■ sediments, may be inferred in the central part of the ?a. The trend of this third group of fold axes parallels major trend of folding in the eastern Santa Monica tuntains. Uplift of the Griffith Park area after the deposition of > Modelo formation resulted in tilting the Modelo to the it along a north-south axis on the eastern end of the liint Hollywood block. The Modelo formation slid along contact with the Feliz pluton to form a low angle mal fault with a thin zone of gouge and to cause some impling of the strata along irregular axes that trend •th -south. The axis of tilting is related to no structural ture of the eastern Santa Monica Mountains ; it may be ated to the Los Angeles River fault, which it probably allels. Numerous minor folds are present in and related to the jor folds in the area, such as drag folds in the over- ned syncline in the Griffith block. GEOMORPHOLOGY 7 he principal topographic feature in this area is the b-trending main ridge that is continuous with the main ' ?e of the Santa Monica Mountains and separated from ^•y the low gap that is Cahuenga Pass. This ridge does i, appear to be controlled by geologic structure, for it is i| parallel to the regional strike and is everywhere north ) :he tectonic axis of the eastern Santa Monica Moun- ;« is. The range is asymmetric, being steeper on the north ; |: is largely a result of the greater rainfall on the south i; of the mountains. 'ahuenga Pass is underlain by soft shaly rocks and is ) .veen two areas of hard resistant rocks. Ridge-forming I 1st ones of the Topanga formation are on the south - ft t side of the pass. The hard sandstones of the Cahuenga b' s crop out on the east side of the Cahuenga fault zone, B^eh is on the east side of the pass. Thus Cahuenga Pass p.oably owes its existence to the presence of the soft n! ;s of the Hollycrest formation sandwiched between two U is of resistant rock. The Los Angeles River conceivably n • have flowed through this pass prior to the last uplift R le Santa Monica Mountains. he minor topographic features of the Griffith Park I are closely related to the geologic structure, more so fin is true elsewhere in the eastern Santa Monica Moun- tains. Many stream canyons follow fault contacts between locks of unlike resistance to weathering ; the best example is Brush Canyon which follows the southern part of the Brush Canyon fault. To an extent this close relation is surprising, inasmuch as gouge and breccia zones along faults in this area are very thin. The south side of the main ridge, east of Mount Holly- wood, is a compound fault-line scarp. The escarpment on the south side of Cahuenga Peak may be a fault-line scarp in part. The hogback containing Cahuenga Peak owes its existence to the underlying resistant Cahuenga conglom- eratic sandstone and sandy conglomerate. GEOLOGIC HISTORY The following sequence of events seems a probable ex- planation of the evolution of this area. 1. Plutonic intrusion of gabbro into unknown rocks. 2. Hypabyssal intrusion of basalt and diabase into the gabbro. 3. Intrusion of the Vermont pluton, in two stages, into the older basic igneous rocks, and metamorphism of these older rocks. 4. Intrusion of the Lar pluton under shearing stress in the north- ern part of the area. 5. Shearing and brecciation of the basement rocks between the Lar pluton and the Vermont pluton as a result of the same forces that caused the foliation of the Lar pluton, and brecciation of the Lar pluton in the Cahuenga Peak block. This period of oro- genic activity probably resulted in the formation of the Ca- huenga, the Brush Canyon, the Griffith, and the Hollister faults, and in the formation of the troughs that controlled deposition of the sediments. 6. Intrusion of the Feliz pluton ; the region of intrusion was con- trolled in part by the zones of breccia in the older rocks. 7. Brecciation of the part of the Felix pluton that was intruded along the site of the Griffith block. 8. Shearing of the quartz diorite microbreccia in the Cahuenga Peak block. 9. Intrusion of malchite in the Lar pluton in the Riverside block. Intrusion of andesite porphyry dikes into the quartz diorite microbreccia in the Cahuenga Peak block, under near surface conditions. 10. Erosion and partial subsidence of the area. 11. Deposition of the Griffith beds on the planed surface of base- ment rocks ; the lower part was deposited in the sea ; the upper part grades up into a fanglomerate derived from the Verdugo Hills, which were emergent at this stage. 12. Folding of the Griffith beds, and downfaulting of part of the folded rocks into the Griffith block. 1.3. Erosion to an area of gentle relief, followed by gradual subsid- ence. 14. Deposition of the Cahuenga beds. If). Folding of the Cahuenga beds into a gentle anticline, and then down faulting into the Cahuenga Peak, the Ferndell, and the Griffith blocks. 16. Erosion of the area, with the formation of a highland area of basement rocks in the Mount Hollywood block, east of the Fern- dell fault-line scarp. 17. Subsidence of the area with the Ferndell and Griffith blocks forming rapidly subsiding troughs. 15. Deposition of the lower member of the Topanga formation ; volcanic activity concentrated in the Ferndell block and along the southern side of the Griffith block ; volcanoes of basalt in the Riverside block and in the eastern end of the Mount Holly- wood block. 19. Uplift and deformation along the northeast-trending anticlinal axis. 20. Erosion, followed by subsidence and deposition of the middle member of the Topanga formation. Very little volcanic activity. The areas that were eroded were underlain principally by basalt. 21. Uplift and deformation along the northeast-trending anticlinal axis. 22. Erosion,* followed by subsidence and deposition of the upper member of the Topanga formation ; explosive eruption of alkali trachyte ash. 23. Uplift and deformation along the northeast-trending anticlinal axis. 28 Special Report 33 24. Erosion, followed by subsidence and deposition of the Holly- crest formation. Local deposition of a basal conglomerate in the Griffith block, which was a rapidly subsiding trough. 25. Uplift and deformation of the area to produce northwest-trend- ing synclines. 26. Erosion, followed by complete subsidence and deposition of the Modelo formation. 27. Uplift and deformation. (Direction of deformation being con- trolled by movement along the Los Angeles River fault?) 28. Erosion and deposition of alluvium in stream canyons and in alluvial fans. 29. Uplift, followed by erosion of the older alluvium and deposi- tion of the alluvium now accumulating in the bottoms of can- yons and on alluvial fans. ECONOMIC GEOLOGY Quarries Three quarries are present on the east slope of Brush Canyon in Miocene basalt, Quarrying- was begun by the Los Angeles Stone Company (Merrill, 1916, p. 486). The product was crushed stone, used mainly for concrete ag- gregate. The capacity of the plant was 1,000 tons per day. A large tonnage was removed ; stockpiles, now overgrown with brush, are present in several places near the quar- ries. Some of this stone was used in home construction in the surrounding area. In 1921, the quarry was purchased by the Union Rock Company (Tucker, 19*21, p. 322) ; this company increased the capacity to 2,000 tons per day in 1926 (Tucker, 1927, p. 342). The quarries were abandoned in 1929 (?), and are now used occasionally for a movie location. A small quarry is on the west side of Brush Canyon in the quartz diorite microbreccia ; it is abandoned. On the eastern slope of the canyon west of Brush Canyon, the remains of a screening plant, obviously used in connec- tion with this quarry, is present, Some of the material from this quarry was used by local residents for retain- ing walls. Information on this quarry was not available. The Los Angeles Park Department is quarrying and crushing the Lar quartz diorite on the north side of the Riverside block and west of Hollister Drive for use in surfacing park roads and playgrounds. Mines A 100-foot adit is present in the Cahuenga breccia in a small canyon on the west side of Brush Canyon. Local tra- dition has this mine being an old Spanish gold mine. A short adit is present in basalt on the east side of Brush Canyon east of the above-mentioned mine. The adit is ru- mored to be an abandoned copper prospect, but no copper minerals were to be found. The Mexicans dug a lime kiln in the side of a bill on the north side of the Riverside block, just east of Hollister Drive. Calcite was obtained from thick veins along faults in the Lar biotite quartz diorite nearby and in the Holly- crest conglomerate in the small hill, about a wile west of the kiln. Blocks of shell limestone were also brought from the south side of Mount Hollywood for calcining. Hollywood Lake The reservoir called Hollywood Lake is a part of the Owens River aqueduct system, and was built as an im- pounding reservoir to serve Hollywood and the surround- ing area. The dam is named Mulholland Dam and was built in 1924-25 by the Los Angeles Department of Water and Power. The dam is located in Weid Canyon east of Cahuenga Pass ; it is 210 feet from foundation to crest 933 feet long and 16 feet wide at the crest. Following the failure of the St, Francis Dam in 1928 public opinion forced numerous investigations of the Mul holland Dam to be made to determine the safety of th< structure (Anonymous, 1934, p. 558). Despite repeatec assurances from the investigating boards that the struc ture was safe, it was finally necessary to construct ar earthfill on the downstream face of the dam. This con struction was admittedly for the psychological effect : Filling the canyon below the dam and planting shrub: and trees would change the apparent menace to a pleasing view carrying no suggestion of a dam. " A small dam wa: subsequently built in the northern part of Hollywoot Lake to provide additional reservoir capacity. Engineering Geology At one time, the City Council of Los Angeles considers the possibility of providing further access to San Fer nando Valley by tunnels through the Griffith Park are (Jessup, 1933) ; seven alternate routes were suggested. A present the City of Los Angeles is preparing to drive ai. aqueduct tunnel from Brush Canyon to Hollywood Lak( REFERENCES Anonymous (1034) Mulholland Dam backed by earth fill again* downstream face : Engineering News Record, vol. 112, p. 558-56( Campbell, I., and Sehenck, E. T. (1950) Camptonite dikes nea Boulder Dam, Arizona : Am. Miner., vol. 35, pp. 671-692. Elam, J. G. (1948) Geology of the Seminole quadrangle, Los Angek County, California : Unpub. M.A. thesis, University of Californi at Los Angeles. Hanna, G. D. (1926) Paleontology of Coyote Mountain, Imperii County, California : Cal. Acad. Sci., Proc. ser. 4, vol. 14, p. 247-50: Hazenbush, G. C. (1950) Geology of the eastern parts of the Dr Canyon and Las Flores quadrangles, Los Angeles County, Cal fornia : Unpub. M.A. thesis, University of California at Los Ai. geles. Hoots, H. W. (1931) Geology of the eastern part of the Sanl Monica Mountains, Los Angeles County, California : U. S. Gee Surv. Prof. Paper 165-C, pp. 83-134. Hoots, H. W. (1932) Generalized geology of the eastern part of tl Santa Monica Mountains in Guide Book 15, 16th Internat. Gee Congr., pp. 40-43. Jessup, .1. J. (1933) Report on Griffith Park Tunnel plan, City i Los Angeles, February 1933, to the City Council of Los Angele Klecker, J. B. (cal 935) Geologic map of Griffith Park, Unpu Senior Problem, University of California at Los Angeles. Knopf, A. (1929) The Mother Lode system of California: U. Geol. Surv. Prof. Paper 157. Kuenen, Ph. H., and Migliorine, C. I. (1950) Turbidity currents; a cause of graded bedding : Jour. Geol., vol. 58, pp. 91-127. McGill, J. T. (1948) Geology of a portion of the Las Flores and P Canyon quadrangles, Los Angeles County, California. Unpu M.A. thesis, University of California at Los Angeles. Merrill, F. J. H. (1916) Mines and mineral resources of Los Angel County, Orange County and Riverside County : California Mi Bur. Rept. 15, p. 486. Miller, W. J. (1934) Geology of the western San Gabriel Mountai of California : Univ. California Publ. Math, and Phys. Sci., vol. pp. 1-114. Neuerburg, G. J. (1951a) Minerals of the eastern Santa Moni Mountains, Los Angeles City : Am. Mineralogist, vol. 36, p. 15 159. Neuerburg, G. J. (1951b) Evidence of a major fault truncating t eastern end of the Santa Monica Mountains, California: (abst Geol. Soc. America Bull., vol. 62, p. 1509. Neuerburg, G. J. (1951c) Petrology of the pre-Cretaceous rocks the Santa Monica Mountains, California: Unpub. Ph. D. thes University of California at Los Angeles. Petti John, F. J. (1949) Sedimentary rocks, Harper and Brothe: New York. Stepper, A. W. (1931) Geology of the Glendale-Eagle Rock distric Unpub. Senior Problem, Univ. California, Los Angeles. Geology of Griffith Park Area, Los Angeles County 29 iening, J. N. (1951) Geology of part of the eastern Santa Monica Tucker, W. B. (1921) Los Angeles field division, Los Angeles Hintains : Unpub. M.A. thesis, University of California at Los County: California Min. Bur. Kept. 18, p. 322. lgeles. Tucker, W. B. (1927) Los Angeles field division, Los Angeles x, J. N. (1950) Geology of the' northern part of the Santa County: California Min. Bur. Rept. 22, p. 342. onica Mountains between Beverly Glen and Laurel Canyon Woodring, W. P., Bramlette, M. N., and Kew, W. S. W. (1946) mlevard : Unpub. M.A. thesis, University of California at Los Geology and paleontology of Palos Verdes Hills, California : U. S. lgeles. Geol. Surv. Prof. Paper 207. Printed in California state printing office « 4-53 2M 1 B o„ 1 «"■ I' ■' >:':j ; -i§;v^Jov 1 sjzW&TPV^T: o ° «~\ w \ oo^^r * GEOLOGIC MAP AND STRUCTURE SECTIONS OF THE GRIFFITH PARK AREA LOS ANGELES COUNTY, CALIFORNIA Geology by George J. Neuerburg, 1945-1949