Prepared in cooperation with the SAN BERNARDINO VALLEY MUNICIPAL WATER DISTRICT, U.S. FOREST SERVICE OPEN-FILE REPORT 01-173 U.S. DEPARTMENT OF THE INTERIOR (San Bernardino National Forest) and the CALIFORNIA DIVISION OF MINES U.S. GEOLOGICAL SURVEY Version 1.0 AND GEOLOGY 117 30' 117 22' 30" OLDER SURFICIAL DEPOSITS—Sedimentary units that are moderately small, poorly formed feldspar phenocrysts. Foliation defined by oriented CORRELATION OF MAP UNITS consolidated and slightly to moderately dissected. Older surficial deposits have 34 15' 34 15' hornblende and biotite, commonly as dark, multi-grained, flattened inclusions. upper surfaces that are capped by moderately to well developed pedogenic soils Contains large septa of marble, gneiss, and schist, the latter two incorporated in (A/AB/B/Cox profiles and Bt horizons as much as 1 to 2 m thick and have maximum varying degree into the tonalite; some rock contains scattered garnets having hues in the range of 10YR 5/4 and 6/4 through 7.5YR 6/4 to 4/4 and mature Bt kelyphytic rims. Along southeast side includes: horizons reaching 5YR 5/6). Includes: Ktm Mylonitized tonalite of San Sevaine Lookout (Cretaceous)—Mylonitized Qw 1 2 Qof Old alluvial-fan deposits (late to middle Pleistocene)—Unconsolidated to well tonalitic rocks. Homogeneous, gray, porphyroblastic mylonite zone 200 to 400 Qaf Qw Qf Qc Qt Qsw Qls consolidated alluvial-fan deposits of coarse-grained sand to bouldery alluvium. m in width. Mylonite is tonalite composition, but ranges to diorite and Qw1 Qf ? ? 1 These old fans have moderately to well dissected surfaces. Includes from monzogranite composition locally. Very fine grained to aphanitic, having youngest to oldest: porphyroclasts of plagioclase, quartz, and most notably porphyroclasts or Qyf Qya 5 5 Qof Old alluvial-fan deposits, Unit 3 (late Pleistocene)—alluvial-fan deposits having Holocene 3 porphyroblasts of hornblende as much as 3 cm in length. Most elongate moderately dissected surfaces and stage S4 soils porphyroclasts or porphyroblasts show strong preferential orientation down dip. Qyf4 Qya4 Qof2 Old alluvial-fan deposits, Unit 2 (late Pleistocene)—alluvial-fan deposits having Includes dark-gray to black, aphanitic mylonite and ultramylonite layers Qyw Qyf Qyf3 Qyt Qyls well-dissected surfaces and stage S4 to stage S3 soils (psuedotachylyte) approximately 3 cm thick. Qof1 Old alluvial-fan deposits, Unit 1 (middle Pleistocene)—alluvial-fan deposits Schist and gneiss (Paleozoic)—Well foliated schist and gneiss exposed on Qyf2 having well-dissected surfaces and stage S3 soils Penstock Ridge and areas west of Lytle Creek. Composition of schist and QUATERNARY Qoa Old alluvial-valley deposits (late to middle Pleistocene)—Low terraces of gneiss is variable, but most is biotite-bearing Qyf1 gravelly sand Schist, gneiss, monzogranite and granodiorite (Paleozoic)—Schist and gneiss Qoa1 Old alluvial-valley deposits, Unit 1 (middle Pleistocene)—Low terraces of ( ) mixed with large proportion of monzogranite and granodiorite (Kg) Qof gravelly sand Schist, gneiss, and tonalite (Paleozoic)—Schist and gneiss ( ) mixed with large 3 CENOZOIC Qols Old landslide deposits (late to middle Pleistocene)—Dissected slope-failure proportion of tonalite of San Sevaine Lookout (Kt) Qols Qof Qof2 Qoa deposits that consist of unconsolidated to moderately consolidated, massive to fz Pleistocene m Granulitic gneiss, mylonite, and cataclasite (Proterozoic?)—Prograde granulitic crudely stratified rock debris and rubble. Deposits are probably inactive under gneiss that is largely retrograded to amphibolite and greenschist grade mylonite Qof Qoa 1 1 current climatic conditions and moderate to strong ground-shaking conditions and cataclasite. Granulitic gneiss includes quartz-feldspar gneiss, garnet- VERY OLD SURFICIAL DEPOSITS—Sediments that are slightly to well quartz-feldspar gneiss, amphibolite, garnet-pyroxene rich rocks, and spinel- Qvof 2 consolidated to indurated, and moderately to well dissected. Upper surfaces are pyroxene rich rocks. Gneiss includes layers of coarse-grained marble (m) that Qvow Qvof Qvols capped by moderate to well developed pedogenic soils (A/AB/B/Cox profiles having are progressively more mylonitic southward in unit. Includes: Qvof1 Bt horizons as much as 2 to 3 m thick and maximum hues in the range 7.5YR 6/4 m Granulitic gneiss, mylonite, and cataclasite, unretrograded and 4/4 to 2.5YR 5/6) Pliocene and (Proterozoic?)—Same protolith as retrograded rock ( ), but most of Tc Tc Ts 1 Miocene Qvow Very old wash deposits (early Pleistocene)—Unconsolidated to slightly prograde mineralogy and texture is preserved. Unit is compositionally layered, consolidated coarse-grained sand to bouldery alluvium but unfoliated garnet-pyroxene-plagioclase rock. Includes small areas of Td3 Ta Miocene TERTIARY Qvof Very old alluvial-fan deposits (early Pleistocene)—Unconsolidated to well- mylonitized rocks and pods of white, mylonitic marble (m) consolidated alluvial-fan deposits of coarse-grained sand to bouldery alluvium. gnm Cataclastic gneiss (age unknown)—Cataclastic and mylonitic biotite gneiss Many very old fans are characterized by extremely dissected surfaces. Includes intruded by granitic rocks which have also been mylonitized. Gneiss is layered, Ttp Ttd Oligocene from youngest to oldest: intensely folded, and contains amphibolite grade mineral assemblages. Qvof2 Very old alluvial-fan deposits, unit 2—alluvial-fan deposits having extremely Restricted to Scotland area in northwestern part of quadrangle. Gneiss contains dissected surfaces and stage S2 soils scattered pods of white, coarse- to very fine-grained, mylonitic marble too m Qvof1 Very old alluvial-fan deposits, unit 1—alluvial-fan deposits having extremely small to show at map scale. Includes: MESOZOIC dissected surfaces and stage S1 soils Chloritized, cataclastic granitic rock (age unknown)—Cataclastic biotite Kmg Kgm Kg Kgc cgm1 CRETACEOUS Qvols Very old landslide deposits (early Pleistocene)—Well dissected slope-failure gneiss containing large proportion of cataclasized, chloritic granitic rocks. deposits that consist of moderately consolidated, massive to crudely stratified Restricted to Scotland area in northwestern part of quadrangle, adjacent to Kt Ktm1 rock debris and rubble. Deposits are probably inactive under current climatic cataclastic gneiss unit (gnm) conditions and moderate to strong ground-shaking conditions PALEOZOIC fz Crushed rock in fault zones (Holocene to late Tertiary)—Gouge and crushed and brecciated rock developed along Lytle Creek and San Jacinto Fault zones GEOLOGIC SUMMARY Conglomerate (Pliocene and Miocene)—Moderately indurated, gray, massive to m m PROTEROZOIC (?) Tc1 Tc moderately well bedded, non-marine boulder conglomerate. Contains some The Devore quadrangle straddles part of the boundary between two major physiographic interbeds of coarse-grained, moderately indurated sandstone. Found along San provinces of California, the Transverse Ranges Province to the north and the Peninsular Ranges gnm cgm1 AGE UNKNOWN Gabriel Mountain front where conglomerate unconformably underlies units Province to the south. The north half of the quadrangle includes the eastern San Gabriel Mountains Qof2 and Qvof2 and is overthrust by granulitic gneiss ( ). Locally contains and a small part of the western San Bernardino Mountains, both within the east-central part of the conglomerate (Tc1) which has sparse clasts of argillic-altered, silicic volcanic Transverse Ranges Province. South of the Cucamonga and San Andreas Fault zones, the extensive rocks alluviated area in the south half of the quadrangle lies within the upper Santa Ana River Valley, and Ts Arkosic sandstone (Pliocene and Miocene)—Well indurated, indistinctly bedded, represents the northernmost part of the Peninsular Ranges Province. pebbly, tan, arkosic, non-marine sandstone found within the San Andreas fault There are numerous active faults within the quadrangle, including right-lateral strike- zone. Contains abundant 10 to 20 cm-diameter clasts of thouroughly fractured slip faults of the San Andreas Fault system, which dominate the younger structural elements, and NOTE: Subscripts of Quaternary unit lables on map denote grain size granitic rocks and subangular, olive-brown volcanic rocks. Most of unit appears separate the San Gabriel from the San Bernardino Mountains. The active San Jacinto Fault zone characterizing the unit within individual polygons. (e.g. Qyf ) b to be highly deformed, but retains a massive appearance projects toward the quadrangle from the southeast, but its location is poorly constrained not only lg- large boulders s - silty Td Olivine diabase and gabbro (Miocene)—Texturally zoned small pluton consisting within the quadrangle, but for at least several kilometers to the southeast. As a result, the b - boulder gravel c - clayey 3 of aphanitic to fine-grained olivine diabase near margins, grading to coarse- interrelation between it, the Glen Helen Fault, and the probable easternmost part of the San Gabriel g - gravel (cobble through m - marl grained olivine gabbro near its center. Intrudes Oligocene granodiorite of Fault is intrepretive. Thrust faults of the Cucamonga Fault zone along the south margin of the San granule gravel) p - peat Telegraph Peak (Ttp) between Cajon and Lytle Creeks. Contains late- Gabriel Mountains, represent the rejuvinated eastern end of a major old fault zone that bounds the a - arenaceous (very coarse crystallizing, non-discrete pegmatitic clots which are characterized by large south side