Preliminary geologic map and engineering geologic information, Oakland and vicinity, California

Map and map database of susceptibility to slope failure by sliding and earthflow in the Oakland area, California

“…Terrain forms and material deposits created by landsliding (Varnes, 1978) are prominent in the hills in and east of Oakland (Radbruch and Weiler, 1963;Radbruch and Case, 1967;Radbruch, 1969). Most of the large landslide deposits that have been mapped in the area (Nilsen, 1975) are presumed to have resulted from earthflow and translational or rotational sliding.…”

“…In the San Francisco Bay region, the varied prevalence of landsliding with rock type and geologic structure is well documented (Cleveland, 1971;Brabb and others, 1972;Nilsen, Taylor, and Dean, 1976;Bechini, 1993;Haydon, 1995). This control is evident in the greater Oakland area (table 1), for example, where landslides are conspicuous in two major geologic units with high clay content, the Miocene Orinda (Tor) and Briones (Tbr) Formations, but rare in two other major units, the Cretaceous Oakland Conglomerate (Ko) and the Redwood Canyon Formation (Kr) (Radbruch and Case, 1967;Radbruch, 1969;Keefer and Johnson, 1983;Bechini, 1993).…”

“…Which intervals to designate safe or dangerous is subjective and remains a matter of interpretation, as no direct means of calibration is available at this time. However, from field study that has long identified such geologic units as the Briones and Orinda Formations (Radbruch and Case, 1967;Radbruch, 1969;Keefer and Johnson, 1983;Bechini, 1993) as highly likely to fail (their mean spatial frequencies are 0.27-0.28, table 1), it appears that susceptibility values at least as low as 0.20 (yellow on the map) indicate areas of potential instability-depending on the strength and duration of triggering events. Dense clusters of values exceeding 0.30 (light orange on the map) are likely to contain areas of concern.…”

Mapping time-dependent changes in soil-slip-debris-flow probability

“…The selection of shear resistance categories was aided by G.F. Wieczorek (written commun., 1992) who, with coauthors (Wieczorek and others, 1985), developed a categorization of shear strengths for analysis of regional slope instability during earthquakes. In the Oakland hills area, categorization of shear resistance was assisted by the observations of Radbruch (195 7), Radbruch and Case (1967), and Nilsen (1975), and by descriptions of hillside materials units provided by S.D. Ellen and C.M.…”

Digital database of microfossil localities in Alameda and Contra Costa Counties, California

“…The purpose of the associated digital database is to provide a quick and easy means of accessing micropaleontologic data, locality information, and a summary of the interpretations. Data for this study are derived from microfossil samples in the U.S. Geological Survey collections, including new samples collected during field work related to the production of U.S. Geological Survey Open-File Reports and Miscellaneous Field Maps (Blake and others, 2000;Graymer, 2000;Graymer and others, 1994aGraymer and others, , b, 1996Graymer and others, , 2002aHelley and Graymer, 1997a, b) and samples that were collected to support earlier mapping efforts (Hill, 1983;Radbruch-Hall, 1957Radbruch and Case, 1967). The older samples were reviewed for consistency with modern biostratigraphic understanding and revisions made as appropriate.…”