m- ..;t' I 0.. <( :E DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY PREPARED IN COOPERA;riON WITH THE CALIFORNIA DIVISION OF MINES AND GEOLOGY GEOLOGIC MAP OF THE NEWBERRY QUADRANGLE SAN BERNARDINO COUNTY, CALIFORNIA By T. W. Dibblee, Jr., and A.M. Bassett MISCELLANEOUS GEOLOGIC INVESTIGATIONS MAP I-461 -m ..;t' PUBLISHED BY THE U.S. GEOLOGICAL SURVEY I WASHINGTON. D. C. 0.. <( 1966 :E DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP 1- 461 UNITED STATES OEOLOOICAL SURVEY GEOLOGIC MAP OF THE NEWBERRY QUADRANGLE, SAN BERNARDINO COUNTY, CALIFORNIA By T. W. Dibblee, Jr., and A. M. Bassett DESCRIPTION OF MAP UNITS Gravel bar.--Bar of rounded pebbles and coarse sand; deposited by wave action presumably on east SEDIMENTARY AND VOLCANIC ROCKS shore of Manix Lake. Surficial sediments Sand and silt,--Mostly bedded light-gray to light­ bu.ff fine to coarse sand and interbedded light-green­ Unconsolidated valley fill; deposited in valley areas ish-gray silt, clay, and some pebble gravel. Maxi­ and in Mojave River channel; generally undissected. mum total thickness about 40 feet. Grades upward In much of valley area, sediments gradational into into gravel of older alluvium. Deposited probably underlying older surficial sediments; elsewhere un­ in Manix Lake and in part by inflowing streams. conformable on older formations. Age, Recent, prob­ ably in part very late Pleistocene. Composed of the Lake-bed clay.--Light-greenish-gray, faintly bed­ following units: ded, argillaceous to silty clay, and some thin inter­ beds of fine-grained arkosic sands. About 80 feet River sand.--Fine- to coarse-grained arkosic sand in maximum thickness; overlies older gravel; lenses deposited in channel of Mojave River and its tribu­ out westward; grades laterally northward and east­ taries which are incised through alluvium and older ward into, and is overlain by, sand and silt. Yielded surficial sediments. late Pleistocene bird fossils (Howard, 1955). River terrace graveL--Bedded gravel similar to Older surficial sediments older gravel described below. As thick as 50 feet. Deposited on former meander of Mojave River be­ Extensive alluvial gravels and sands that fill valley fore present channel was incised. area; total exposed thickness as much as 250 feet; thickness may be greater in valley area where con­ Windblown sand.--Thin cover and small dunes of cealed under overlying surficial sediments; eroded fine-grained sand composed mostly of quartz and and dissected in areas where exposed and elevated. feldspar, drifted and deposited by prevailing westerly Unconformable on older Pleistocene, Tertiary, and winds on alluvium, clay, and older formations. pre-Tertiary rocks. Age, presumably Pleistocene. Clay.--Light-gray clay or mud; alkaline in Troy Divided into the following units: Lake (usually dry). Older alluvium.--Light-gray, massive to bedded, Alluvium.--Cobble-pebble gravel and sand near cobble-pebble gravel and sand derived mostly from hills, grading outward into sand and silt in level adjacent mountains or hills. Maximum exposed thick­ valley areas; top surface slopes less than 200 feet ness about 90 feet. per mile. Grades downslope into clay. Older graveL--Gray, bedded gravel composed of Alluvial fan graveL--Coarse gravel of unsorted, moderately sorted, rounded cobbles and pebbles most­ subrounded fragments as large as 5 feet in diam­ ly of Mesozoic metavolCanic and Tertiary andesitic eter, derived from adjacent mountains and deposit­ rocks derived from hills to south. Maximum exposed ed as alluvial fans; top surface slopes from 200 thickness about 160 feet. to 350 feet per mile; fragments decrease in size Basalt of Malpais flow downslope as gravel grades into alluvium. Black, hard, vesicular microcrystalline basalt com­ Basalt of Pisgah flow posed of calcic plagioclase laths, pyroxene, olivine, Fresh, hard, black vesicular microcrystalline ba­ finely disseminated magnetite, and very small pheno­ salt composed of calcic plagioclase (partly as laths), crysts of olivine and labradorite; porous, with minute basaltic glass, pyroxene, disseminated magnetite, vugs between grains. Forms several flows with total and small patches of olivine; porous, with minute thickness as much as. 50 feet, thinning northward; vugs between grains. Forms at least one single erupted from Malpais Crater 4 miles south of quad­ ropy lava flow on alluvium and clay; erupted from rangle in late Pleistocene time. Pisgah Crater southeast of quadrangle. Age, Recent, Older fanglomerate and gravel possibly in part Pleistocene. Gray, crudely bedded fanglomerate and gravel com­ Manix Lake Beds posed of poorly sorted, subrounded fragments as large Mostly fine-grained sediments named Manix lake as 2 feet in diameter of pre-Tertiary porphyry com­ beds by Buwalda (1914, p. 444), deposited in a late plex or metavolcanic rocks, plutonic rocks, and Pleistocene lake he called Manix Lake. Well ex­ Tertiary volcanic rocks. Maximum exposed thickness posed 2 1/2 miles east-southeast of Manix; type local­ about 250 feet. In areas north of Mojave River, in­ ity hereby designated from base of lake bed clay ex­ cludes fragments of Tertiary chert and limestone. posed on west bank of Mojave River in NW1/4 sec. In NW1/4 sec. 17, T. 8 N ., R. 3 E., 3 miles south of 15, T. 10 N ., R. 4 E., northwesterly to highway in Newberry, basal 70 feet is buff arkosic sandstone. NW1/4 sec. 4, T. 10 N., R. 4 E. Sediments general­ Unconformable on Tertiary rocks. Age, presumably ly flat lying, but much dissected; conformable on Pleistocene, possibly in part very late Pliocene. older gravel unit. A lacustrine facies of older al­ luvium. Divided into the following units: Sedimentary rocks irregular erosion surface of pre-Tertiary rocks; in Newberry Mountains, within quadrangle, only lower Sequence composed mostly of sedimentary rocks; 6,000 feet of 12,000-foot-thick onlapping sequence maximum exposed thickness possibly 3,000 feet at exposed; in Cady Mountains, within quadrangle, maxi­ south border of quadrangle, less than 2,000 feet else­ mum thickness possibly 5,000 feet. Unfossiliferous. where; unconformable on Tertiary volcanic and sedi­ Age, presumably Miocene or older, on basis of cor­ mentary rocks, especially at south boarder of quad­ relation with rocks of that age in Cady Mountains rangle. Age, Tertiary, presumably late Miocene or quadrangle. Divided into the following rock units as younger. Divided into the following rock units as mapped: mapped: Basalt.--Black, massive, fine-grained to subvitre­ Limestone and claystone.--Light-gray to nearly ous, composed of gray calcic plagioclase and minor white, hard, poorly bedded to massive limestone, in amounts of ferromagnesian minerals and specks of places partly silicified to gray or black chert, and magnetite; commonly contains some small pheno­ interbedded soft greenish-gray claystone. Deposited crysts Of plagioclase and olivine. Forms extrusive in a lake. flows; some flows amygdaloidal. Gradational into Sandstone and claystone.--Light-gray, f ria b 1 e, andesite. In Newberry Mountains, much of basalt locally pebbly, fine- to medium-grained arkosic composed of fine-grained mesh of plagioclase laths sandstone, and interbedded light-greenish-gray clay­ with interstitial pyroxene, olivine, and magnetite, stone or micaceous siltstone. At south margin of commonly with scattered small phenocrysts of plagio­ Cady Mountains contains one or several thin beds of clase and olivine, as seen in thin section; rock porous, white tuff. In sec. 26, T. 10 N ., R. 2 E., north of with minute vugs between grains; friable where weath­ Toomey, yielded late Miocene horse teeth (T. H. ered. In Cady Mountains, much of basalt has sub­ McCulloh, oral communication, 1953). vitreous texture, commonly with.abundant phenocrysts of plagioclase and few of olivine. Volcanic fanglomerate.--Gray, massive fanglom­ erate composed of unsorted subrounded fragments as Basalt breccia and fanglomerate.--Dark-gray to large as 3 feet in diameter of Tertiary andesite, black, massive, in a few places crudely bedded; com­ felsite, and basalt, in matrix of volcanic debris. posed entirely of unsorted angular to subrounded fragments of volcanic rocks as large as 3 feet in Fanglomerate.--In Harvard Hill, dark-gray massive diameter; all or most fragments are of black por­ fanglomerate composed of unsorted fragments, as phyritic subvitreous basalt; in some places are minor large as 1 foot in diameter, mostly of blue-black, admixtures of andesitic fragments. fine-grained mica schist. Near Newberry Mountains, gray massive to very crudely bedded fanglomerate Andesite.--Dark-reddish-brown to gray, massive composed of unsorted, subrounded fragments as large porphyritic volcanic rocks, mostly andesite, but as 5 feet in diameter, mostly of Mesozoic porphyry ranging to latite; most phenocrysts are plagioclase complex and biotite quartz monzonite, some of other (andesine?), in a few places so'me are potassic feld­ plutonic rocks, including hornblende diorite gabbro, spar (sanidine), rarely biotite or quartz; groundmass and few of Tertiary volcanic rocks. Deposited by microcrystalline, composed of plagioclase, some torrential streams as alluvial fans. potassic feldspar, and small amounts of finelydivided hematite and magnetite. In Newberry Mountains, some Bas alt.--Similar to basalt of volcanic and sedimen­ flows in T. 8 N ., R. 2 E., approach basalt in composi­ tary rocks in Newberry Mountains; forms two thin tion; in T. 8 N ., R. 3 E., and in Cady Mountains, some flows in lower part of fanglomerate. of an9_;esite may be