science for a changing world U. S. DEPARTMENT OF THE INTERIOR OPEN-FILE REPORT U. S. GEOLOGICAL SURVEY 00-175 GEOLOGIC MAP AND DIGITAL DATABASE OF THE COUGAR BUTTES 7.5′ QUADRANGLE, SAN BERNARDINO COUNTY, CALIFORNIA Version 1.0 SUMMARY PAMPHLET: LATE CENOZOIC DEPOSITS OF THE COUGAR BUTTES 7.5′ QUADRANGLE, SAN BERNARDINO COUNTY, CALIFORNIA By Robert E. Powell1 and Jonathan C. Matti2 2000 Prepared in cooperation with Mojave Water Agency California Division of Mines and Geology This database is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. U.S. Geological Survey 1 904 W. Riverside Avenue, Spokane, WA 99201-1087 2 520 N. Park Avenue, Tucson, AZ 85719 Open-File Report 00-175, The Geologic Map and Digital Database of the Cougar Buttes 7.5' Quadrangle, San Bernardino County, California, and this summary pamphlet have been approved for release and publication by the Director of the U.S. Geological Survey. The geologic map, digital database, and summary pamphlet have been subjected to rigorous review and are a substantially complete representation of the current state of knowledge concerning the geology of the quadrangle, although the USGS reserves the right to revise the data pursuant to further analysis and review. This Open-File Report is released on the condition that neither the USGS nor the United States Government may be held responsible for any damages resulting from its authorized or unauthorized use. Open-File Report 00-175 is available on the Web at http://geopubs.wr.usgs.gov. 2 INTRODUCTION the north piedmont of the San Bernardino Mountains and the Cougar Buttes inselberg. The Southern California Areal Mapping Structurally and geomorphically, Lucerne Valley Project (SCAMP) of Geologic Division has is a closed desert basin that is flanked to the undertaken regional geologic mapping south by the San Bernardino Mountains and investigations in the Lucerne Valley area co- ringed to the north by highlands in the Mojave sponsored by the Mojave Water Agency and the Desert, including the Granite Mountains, San Bernardino National Forest. These Sidewinder Mountain, Stoddard Ridge, the Ord investigations span the Lucerne Valley basin Mountains, and Cougar Buttes. The basin has from the San Bernardino Mountains front evolved in conjunction with uplift of the San northward to the basin axis on the Mojave Desert Bernardino Mountains and with displacement on floor, and from the Rabbit Lake basin east to the right-lateral faults of the Mojave Desert. Old Woman Springs area. Quadrangles mapped Climatic fluctuations and tectonism have led to include the Cougar Buttes 7.5' quadrangle, the an evolving landscape and have generated a wide Lucerne Valley 7.5' quadrangle (Matti and variety of Quaternary surficial deposits others, in preparation b), the Fawnskin 7.5' associated with various landforms in and around quadrangle (Miller and others, 1998), and the Lucerne Valley (Powell and Matti, 1998a,b). Big Bear City 7.5' quadrangle (Matti and others, Geomorphically, Lucerne Valley is a bolson in preparation a). The Cougar Buttes quadrangle with a central playa fed by alluvial fans has been mapped previously at scales of emanating from the surrounding bedrock 1:62,500 (Dibblee, 1964) and 1:24,000 (Shreve, mountain ranges. Intervening between the 1958, 1968; Sadler, 1982a). principal fans are broad piedmont slopes covered In line with the goals of the National by thin veneers of Pleistocene and Holocene Cooperative Geologic Mapping Program deposits. These veneers, including slopewash (NCGMP), our mapping of the Cougar Buttes and alluvium, mantle pediments beveled across quadrangle has been directed toward generating tilted Pliocene and early Pleistocene sedimentary a multipurpose digital geologic map database. strata onto underlying igneous and metamorphic Guided by the mapping of previous rocks. These surfaces are most prominent on investigators, we have focused on improving our Cougar Buttes, a granite inselberg encircled by a understanding and representation of late Pliocene pediment apron, but are present on the piedmonts and Quaternary deposits. In cooperation with the of all the ranges around Lucerne Valley, Water Resources Division of the U.S. Geological including the San Bernardino Mountains. Survey, we have used our mapping in the Cougar Inselbergs on the north piedmont of the San Buttes and Lucerne Valley quadrangles together Bernardino Mountains include the bedrock ridge with well log data to construct cross-sections of on the east margin of the Cougar Buttes the Lucerne Valley basin (R.E. Powell, quadrangle south of State Highway 247 and the unpublished data, 1996-1998) and to develop a bedrock ridge just southeast of the town of hydrogeologic framework for the basin. Lucerne Valley in the Lucerne Valley Currently, our mapping in these two quadrangles quadrangle. Moreover, parts of the range-front also is being used as a base for studying soils on itself just south of the Cougar Buttes quadrangle various Quaternary landscape surfaces on the appear to rise at the upper margin of a piedmont San Bernardino piedmont (Eppes and others, erosion surface that is rather like a pediment. 1998). In the Cougar Buttes quadrangle, we have Structurally, the Lucerne Valley basin endeavored to represent the surficial geology in a originated as part of broad trough that developed way that provides a base suitable for ecosystem coincident with uplift of the San Bernardino assessment, an effort that has entailed Mountains during late Pliocene and Quaternary differentiating surficial veneers on piedmont and time. The trough extends eastward through Fry pediment surfaces and distinguishing the various and Johnson valleys and westward to the San substrates found beneath these veneers. Andreas fault near Cajon Pass, where it accumulated deposits of the late Pliocene upper Geologic setting Crowder Formation (Phelan Peak deposits of Meisling and Weldon, 1989) and the Pleistocene The Cougar Buttes 7.5′ quadrangle is located Harold Formation and Shoemaker Gravel along the southern margin of the western Mojave (Dibblee, 1967a; Foster, 1982; Meisling and Desert province (fig. 1). The quadrangle Weldon, 1982, 1989). The trough formed as a straddles the east half of Lucerne Valley between downwarp in the basement that accompanied the 3 117° 30' 117° 15' 117° 00' 116° 45' 116° 30' Sto S dd t 0612mi ar a d t Rid e ge Mountains 01020km Ord D E S E R T s Sidewinder n i H a t Mountain i g n h E w u V a o J A y M O 2 4 M 7 s Victorville ain t Camp un Cougar Buttes 7.5' o e M ak y L Quadrangle r Apple Valley e F rn te e i c ° n u ° 34 30' R 34 30' S ra L F ta G o ry te c C k o V u a Rabbit ga l r le Lake Lucerne Pickaninny B y Soggy u Lake Butte tt es J Lucerne Valley R oh Hesperia o ns Valley H a Stat on ig d Blackhawk e V hw Landslide all ay Old Woman ey 18 Springs C Highway 247 u Creek s Blackhawk Cushenbury h S e Canyon Springs C n b A a u n r y y Cajon N o n Pass Arrastre B E R S N A N R D A I I N O M O U N T ar Lake 34° 15' Big Be 34° 15' 117° 30' 117° 15' 117° 00' 116° 45' 116° 30' Figure 1. Index map for Cougar Buttes 7.5' quadrangle and vicinity uplift of the San Bernardino Mountains. As it cycles of weathering and erosion, perhaps grew, the trough received sediment from the extending as far back in time as the Cretaceous rising mountain range to the south and the (Vaughan, 1922; Dibblee, 1967a; Meisling and highlands in the Mojave Desert block to the Weldon, 1982, 1989). Granitic rocks were deeply north. The development of the trough represents weathered beneath the erosion surface; a major paleogeographic change from the metamorphic rocks were not as deeply weathered Miocene, when fluvial systems transported and uphold some of the inselbergs in and around sediment southwestward from highlands in the the Cougar Buttes quadrangle. As described by Mojave Desert across the future location of the Oberlander (1972), the weathering profile from San Bernardino Mountains (Foster, 1980; the surface down consisted of (1) argillaceous Meisling and Weldon, 1982, 1989; Sadler, red soil (argillic red B-horizon), (2) uniformly 1982c). The trough is segmented where it is saprolitic granitic rocks (~ 40 ft thick), (3) transected by various right-lateral faults of the saprolitic granitic rocks with corestones of less Mojave Desert province, including the Helendale altered granitic rock, and (4) jointed granitic and Old Woman Springs faults. Faults of this rock. Near Old Woman Springs just east of the system control the position of the modern bolson Cougar Buttes quadrangle, Oberlander describes in Lucerne Valley. a complete profile beneath Miocene basalt. In the Cougar Buttes quadrangle, however, we have Mapping approach observed saprolitic granitic rocks and reddened arkosic sandstone beneath basalt, but no argillic Late Cenozoic deposits in the Lucerne B-horizon. The erosion surface was broadly Valley area have accumulated in a basin that planar, especially where developed on granitoid developed along the boundary between the rocks. Transverse Ranges and Mojave Desert As the crust was flexed with the growth provinces. The basin has evolved in response to of the San Bernardino Mountains, the Miocene tectonism associated both with uplift of the San erosion surface was deformed. Where Bernardino Mountains and with movement on downwarped, the surface lies buried beneath the right-lateral fault system of the Mojave younger basinal deposits; where upwarped it has Desert province.