STA TE OF CA L IFOR N IA R L W R R N G ov e rn or EA A E . DEPAR TMENT OF NATUR AL R ESOURCES W R R N T HA N Di re c tor A E . NUM . DIVISION OF MINES F R R Y B N G SA N FR N C l l E UILDI . A ISCO L F P EN KIN S Chi O A . I . e f SA N FR A NCISCO BULLETIN 1 67 JUNE 1 953 GEOLOGY OF THE OR TIGA LITA PEA K QUA DR A NGLE CA LIFOR NIA By LOUIS I. BR IGGS . IR . LIBR AR Y UNIVER SITY OF CA L IFOR NIA DA VIS L E T TE R OF TR A N SM I T TA L T o His E x c e llen c y The HONORABLE E ARL WARREN Go v ernor of th e S ta t e of Ca liforni a D S IR : h on or n 1 67 Ge olo EAR I have the to t ra smit herewith Bulletin , g y o t h e Or ti a li t a P e a k u a dr a n le Ca liforn i a r e a r ed dir e c f g Q g , , p p under the la n O f . D D tion of P Jenki s , Chief of the ivision of Mines , epartment of N a u ra l t Resources . The report includes colored geologic and econom ic mine ral maps , geologic sections , and many other illustrations . The ar ea mapped lies on the west side of the San Joaquin Valley , lar gely within Merced County, although parts of it ar e in San Benito and F resno Coun it a ties . Since desc ribes lar ge number of important oil field formations , it r is of particula interest to oil geologists . E conomic minerals pr esent in the s area a re magnesite , quick ilver , diatomite , gypsum , lime , sand , gravel , and bentonite . r t h . e a The author , Louis I B riggs , J , p r epar ed map and report as doc t ora t e r r thesis equi ed by the University of California . The publication of the results of this pr oj ect r epresents one of the cooperative undertakings D of the ivision of Mines with the University . Respectfully submitted , W - T H M D ARREN . ANNU , i rector Department of Natural Resources 2 6 1 9 53 Februa ry , . CON TE N TS Page A BSTR A CT IN TR ODUCTI ON Geography STR A TI GR A PHY Jurassic system Franciscan group Cretaceous system Wisenor formation Panoche formation Moreno formation Pet r ography of the Upper C r etaceous sediments Tertiary - Quaternary system Laguna Seca formation Tesla formation K r eye nha gen form ation San Pablo formation Oro Loma formation Tulare formation Stream terraces Recent alluvium Landslides GE OL OGI C S TR U CTUR E Folding Faulting Structural history GE OL OGI C HI STOR Y E CON OMI C R E SOUR CE S Quicks ilver Magnesite Diatomite Gypsum Lime Bentonite Sand and gravel Petroleum BI BL I OGR A PHY I L L U ST R AT I O N S m a t h e rt i a l it a 1 . G O Plate eologic p of g Peak quadrangle , California 2 E Ort i a l i t a . conomic map of the g Peak quadrangle , California G Ort i a l i t a 3 . eologic structure sections across g Pe ak quadrangle , California In pocket 4 G T L S H . eologic map of ertiary formations in the aguna eca ills , Merced County , California In pocket Index map showing location of Or t ig a l it a Peak quadrangle Columnar section of rock in Ort iga li t a Peak quadrangle “ Photomicrograph of typical F ranciscan graywacke from Ort iga lit a Peak area Photomicrograph of F ranciscan ph yll on i t e from Or t ig a lit a thrust zone Photomicrograph of F ranciscan pillow basalt from Miner Creek Photomicrograph of F ranciscan m e t a g re e ns t on e from east slope of Ort ig a lit a Peak Photomicrograph of pegmatoid vein in F ranciscan quartz gabbro sill south of Or t ig a l i t a Peak _ Photomicrogra ph of e x - solution patterns of magnetite - ilmenite altered to leucoxene and quartz Photo showing quartz gabbro sill on north bank of Miner Creek Photo showing slump bedding in silt strata Photo showing gnarly bedding of U pper Cretaceous sandstone Photo showing concretions in U pper Cretaceous rocks Photo showing conglomerate series i n north branch of L os Banos Creek Photo showing sandstone penetrating overlying conglomerate Photomicrograph of U pper Cretaceous s ubg ra ywa c ke _ Histogram of rock types in coarse conglomerate at Or t iga li t a Creek and L os Banos Creek Photo showing concretion in Panoche formation Photo showing diatomaceous shale in Moreno formation Photo showing formations in Rattlesnake Canyon Photo showing outcrop of K reye n h a g e n shale on Oro L o rna Creek Photomicrograph of jarosite and glauconite Photomicrograph of jarosite crystals and clusters Photo showing disconformity separating shale and lower member of K re y e nh a ge n formation K re en h a e n Sa n L Photo showing y g shale , Pablo beds , and Oro oma formation Photo showing view north across Dog L eg Creek _“ Photomicrograph of sandstone from base of S a n Pablo formation Photo showing T ulare formation underlain by Moreno shale in cliff on tributary to Ort iga l it a Creek Photo showing Piedra Azul fault i Ort i a l t a . 1 8 T . 1 2 S R . 1 0 E . Photo showing view down g Creek in sec , Photo showing view north along crest of L aguna Seca Hills Photo showing badl a nd topography in T ulare beds Photo showing Mercy quicksilver mine , southern workings Photo showing remains of Scott furnace of Merc y quicksilver mine GE OL OGY OF THE OR TI GA L I TA PEA K E AL I F R % QUA DR AN GL , C O NIA “ L OU I S I . B S J R . By RIGG . A BST R A CT Or t iga li t a Peak quadrangle is in the Coast R anges bordering the Sa n Joaquin l x 5 L os B . T h e D Va ley , appro imately miles south of anos small part of iablo Range in the southwestern portion of the mapped area is underlain by F ranciscan ( U ppe r i s e r e n Jurassic ) graywacke , chert , and greenstone ntruded by quartz gabbro and p h llon i t e s Or t i a li t a tine , and locally converted to glaucophane schists and p y along the g F thrust , the major structural element of the area . ranciscan rocks have been thrust U northeastward over pper Cretaceous conglomerate , sandstone , and shale , and locally Wisenor shale of L o wer Cretaceous ( Horsetown ) age is exposed beneath the fault T h e U surface . thickest known section of pper Cretaceous rocks in California ( some feet ) underlies the foothill belt to the east of the thrust ; it consists of the Panoche formation ( sandy shale , massive concretionary sandstone , and a coarse con glomerate ) overlain by the Moreno fo rmation ( purplish organic shale and sandstone ) . - Rel atively thin bedded T ertiary s edimen ts fringe the eastern edge of the foothills . T n L S r s h hey i clude aguna eca ( Paleocene ) conc etionary sandstone , siltstone , and ale , n a x i t ic K r e e nh a e n T esla ( a u sand and shale , y g diatomite and glauconitic sandstone E S a n o - e of ocene age , Pabl ( Miocene Pliocene ) bentonitic sandston , shale , and con ' L F - 1 1 P l io glomerate , and Oro oma ( Pliocene ) gravels , sands , and silts . lat lying % 1 are ( Pleistocene ) reddish gravel s and white - weathering silt and marl overlap the old e r L i formations and obscure much of the tilted bedrock series , especially near ttle Panoch e Creek . T h e major uplift of D iablo Range occurred during the upper Pliocene orogeny a long the Or t ig a li t a thrust which forms the eastern structural element of D iablo Range 1 3 0 . D for some miles islocation in the thrust zone near the end of the Jurassic period , D ia bl a n i probably during the orogeny , is ndicated by coeval developmen t of glaucophane h ll on it e s i schists and p y in apparent equilibrium , and was accompanied by intrus on . S t h e n of ultrabasic igneous masses ubsequent to Jurassic deformation , deformi g forces have squeezed the serpentinous ultrabasic rocks into faults a n d fractures of the dis r u t e d F p ranciscan rocks in the thrust zone during the upper Pliocene orogeny . E i conomic resources nclude magnesite , quicksilver , diatomite , gypsum , lime , sand , gravel , and bentonite ; however , sand , gravel , and gypsum are the products success fully exploited from this area to date . At least 7 holes have been drilled for petroleum but all have been abandoned . IN T R ODU CT IO N Ort i a lit a a n g Pe k quadrangle, delimited by meridia s W l est and by paralle s north , lies largely within Merced County, although it extends into parts of San Benito and Fresno Coun ties .