Abstract A major debris flow occurred on January 4,1982, in the Oddstad Boulevard area of Pacifica, California. The flow emanated from a previously unrecognized colluvium-filled swale (one of many making up first-order drainages in the region), moved down a 21°, 172-m-long slope, and extended into an urban area. The failure involved the upper 4.5 m of a 6.1-m-thick colluvial section in the upper of two bedrock basins underlying the swale. Soil-stratigraphic measurements show that upper-basin colluvium accreted slowly to form a cumulic soil profile, characterized by thick surface (mollic epipedon) and subsoil (argillic) horizons. An approximately 500-yr-old mean residence time (MRT) radiocarbon date from the prefailure mollic epipedon indicates that the average sedimentation rate was about 0.6 m/1,000 yr and, accordingly, that colluviation began at least 8,000 to 10,000 yr ago. In contrast, the lower basin is characterized by at least four pre-1982 slide deposits. These deposits emanated almost wholly from within the lower basin, and are distinguished by clast lithology and angularity, and by the local presence of capping buried paleosols. Radiocarbon MRT dates of approximately 2 to 3 ka for the upper, older debris flows, and the presence of a moderately developed argillic horizon on an underlying flow, suggest that lower basin failure recurrence is on the order of 1,000 to 4,000 yr. A simple, three-stage evolutionary model for the Oddstad swale is postulated for engineering-geologic comparisons with swales elsewhere: (1) initial basin incision by fluvial processes in late Pleistocene time; (2) change of climatic regime and resultant colluvial filling of the upper basin in Holocene time; and (3) exhumation and renewed fluvial incision of the upper basin following the 1982 debris flow.

Abstract This site is located adjacent to the California coast in northern San Mateo County, about 15 mi (25 km) south-southwest of downtown San Francisco (Fig. 1). From San Francisco, take 1–280 south to its intersection with California 1, then follow California 1 southward for approximately 9 mi (15 km) to San Pedro Avenue in Pacifica. From the central San Francisco Peninsula, take California 92 westward to its intersection with California 1 in Half Moon Bay, then proceed northward on California 1 for approximately 10 mi (16 km) to San Pedro Avenue in Pacifica. From the southern San Francisco Peninsula or Santa Cruz County, take California 1 north to San Pedro Avenue in Pacifica. The Shelter Cove locality (Stop 1) can be reached by taking San Pedro Avenue west for three blocks from California 1, turning north on Danmann Road, and proceeding two blocks north to Shelter Cove Road. At present (July 1986), Shelter Cove Road is a privately maintained access that has sustained substantial landslide damage and is passable only on foot. The property at Shelter Cove is private, and permission to enter must be obtained from the owners (Telegan Realty, Pacifica, California). Roadcuts along California 1 are located south of San Pedro Avenue. Stop 2 is located 0.7 mi (1.1 km) to the south on the northwest side of the highway. Stop 3 in the Devil’s Slide area is located 0.6 mi (1 km) farther south along California 1 and Stop 4 another 0.7 mi (1.1 km) to the south. Stops 2,3, and 4 are subject to heavy traffic and have limited parking along a narrow, twisting, and dangerous roadway. Exposures are close to the roadway, so great caution should be exercised.

Abstract This site is located adjacent to the California coast in northern San Mateo County, about 15 mi (25 km) south-southwest of downtown San Francisco (Fig. 1). From San Francisco, take 1–280 south to its intersection with California 1, then follow California 1 southward for approximately 9 mi (15 km) to San Pedro Avenue in Pacifica. From the central San Francisco Peninsula, take California 92 westward to its intersection with California 1 in Half Moon Bay, then proceed northward on California 1 for approximately 10 mi (16 km) to San Pedro Avenue in Pacifica. From the southern San Francisco Peninsula or Santa Cruz County, take California 1 north to San Pedro Avenue in Pacifica. The Shelter Cove locality (Stop 1) can be reached by taking San Pedro Avenue west for three blocks from California 1, turning north on Danmann Road, and proceeding two blocks north to Shelter Cove Road. At present (July 1986), Shelter Cove Road is a privately maintained access that has sustained substantial landslide damage and is passable only on foot. The property at Shelter Cove is private, and permission to enter must be obtained from the owners (Telegan Realty, Pacifica, California). Roadcuts along California 1 are located south of San Pedro Avenue. Stop 2 is located 0.7 mi (1.1 km) to the south on the northwest side of the highway. Stop 3 in the Devil’s Slide area is located 0.6 mi (1 km) farther south along California 1 and Stop 4 another 0.7 mi (1.1 km) to the south. Stops 2,3, and 4 are subject to heavy traffic and have limited parking along a narrow, twisting, and dangerous roadway. Exposures are close to the roadway, so great caution should be exercised.

Abstract A storm that occurred January 3-5, 1982 in the San Francisco Bay area precipitated a host of mitigation schemes to provide protection against the now-perceived widespread debris flow/avalanche hazard. These procedures are now being designed and constructed in the Bay area. Removal of colluvium and loose bedrock in the source area mitigates the hazard of debris flows—a costly measure requiring access for equipment. Reinforcement of oversteepened slopes with rock riprap has proven to be an economical and expeditious means of supporting the oversteepened head scarp and flanks of a source area scar. In seismically active regions, the use of riprap for repair of source areas should be carefully scrutinized, especially when considered for critical structure sites. Retaining walls are in common use to support unstable slopes in the source area. Their design is based on at-rest earth pressures that can range from an equivalent fluid pressure of 7,070 N/m 3 to as much as 12,570 N/m 3 . Free-standing baffles of timber or steel, embedded in the main track of a confined debris flow/avalanche, reduce velocity but allow deposition to occur in an area accessible to maintenance equipment. Baffles can be spanned by heavy-gauge chain-link or gabion wire to provide a similar effect. Impact walls capable of arresting and containing more than 150 m 3 of debris, after sustaining an instantaneous impact load of at least 19,640 N/m 3 , are constructed on or at the hillside base. Deflection walls can be designed to direct flows to a specified depositional area. Sites positioned on fans or within drainages of limited area are protected by earthera basins designed for impact and containment of debris. Free drainage of a portion of the downstream face mitigates potentially adverse conditions that can develop due to captured runoff. The embankments are designed for an impact force of at least 19,640 N/m 3 , unless constructed with an upstream baffle system. Lessons learned since 1982 in the San Francisco Bay area have changed the thinking of geotechnical consultants on new hillside development. Numerous sites have been protected by one or more of these engineered mitigation schemes. Thousands of hazardous sites remain, however, that are likely to be impacted by future debris flows/avalanches.

ABSTRACT Summer and winter distribution of foraminifera are similar in Tomales Bay, a long narrow embayment, 64 km north of San Francisco, California. Using three different numerical techniques (cluster analysis, multiple discriminant analysis, and multidimensional scaling), three groups of foraminifera were distinguished. One group including Glabratella ornatissima, Rotorbinella campanulata, and Cribrononion lene characterizes the nearshore turbulent zone near the mouth of the bay, an area of direct marine influence in which wind-driven waves impinge upon the shoreline. Two estuarine groups occupy the bay proper: a middle bay group is composed of Bulimina denudata, Fursenkoina pontoni, Hopkinsina pacifica, Nonionella basispinatus, N. stella, Quinqueloculina ackneriana, and several species of Brizalina; and a group at each end of the bay is composed of Buliminella elegantissima, Buccella tenerrima, Elphidiella hannai, and other less common species. Nearshore turbulent conditions at the northern mouth of the bay grade to estuarine conditions towards the south. Several of the species present in the middle bay group are more characteristic of warmer waters found in southern California and Baja California; these may represent a relict fauna from a time of warmer coastal waters or incursions of species brought by El Nino conditions. In contrast, most species found in the rest of the bay are typical of the colder-water Oregonian Province that reaches from Point Conception in the south to Vancouver Island in the north. The only apparent environmental factor that distinguishes the middle bay from the bay ends is the fine-grained sediment size of the middle bay region. Summer and winter samples showed similar foraminiferal composition and abundance, except in some stations where certain species dominate at one season or the other. The winter middle bay is dominated by Hopkinsina pacifica and Bulimina denudata. Glabratella ornatissima dominated the summer samples in the northernmost turbulent zone at the mouth of the bay.

A comparison of foraminiferal faunal trends in pristine and impacted regions on the continental shelf and slope of the Southern California Bight, as well as variations in the temporal foraminiferal distribution patterns from 1955 to 1998, suggest that the benthic microfaunal communities have been greatly affected by the presence of contaminated sediment near the major outfall sites. Six species were most impacted: Trochammina pacifica, Bulimina denudata, Eggerella advena, Buliminella elegantissima, Nonionella stella, and Nonionella basispinata. The silver contaminant-tolerant and organic-waste indicating species Trochammina pacifica and Bulimina denudata dominated the outfall regions in the mid-century but declined in abundance in the 1990s after sewage treatment and sludge disposal activities improved. Over the same time period, the abundance of Eggerella advena, a pioneer colonizer of formerly impacted waste-discharge sites tolerant of most trace-metal and organic contaminants, increased dramatically on the shelf, whereas Buliminella elegantissima, a nitrogen-favoring taxon, dominated the nearshore regions except at the pristine site. In contrast, the contaminant-sensitive species Nonionella stella and Nonionella basi-spinata dominated the shelf assemblages in pristine to low-impacted areas in the late 1950s and early 1960s but were rare to absent near the outfalls, even after remediation efforts were put into effect. Although most other species patterns, as well as the amphipod survival and sea urchin fertilization tests, show that the enhanced sewage treatment programs improved sediment conditions, the inability of Nonionella stella and Nonionella basispinata to reinhabit formerly colonized areas suggests that not all faunal trends have returned to pre- or early-outfall levels even with remediation. The sensitivity of foraminifers to the presence of contaminated sediments suggests that they are a useful tool in evaluating the impact of anthropogenic contamination on microfaunal communities.

ABSTRACT One hundred and fifty-seven samples from the sea floor off San Diego, California, were studied for both living and total (living plus dead) populations of Foraminifera. Seven benthonic Foraminifera depth assemblages are recognized on the basis of the living distributions and abundances. The boundaries are at depths of approximately 13, 45, 100, 250, 350, and 450 fathoms. Based on the Scripps Institution’s study of hydrography it appears that the 13-fathom boundary may be interpreted as approximating the base of the turbulent zone, the 45-fathom boundary the bottom of the seasonal thermocline, the 100-fathom boundary the bottom of the California Current, the 250-fathom boundary the top of the permanent thermocline, the 350-fathom boundary the oxygen minimum layer, the 450-fathom boundary the bottom of the permanent thermocline. The shallowest assemblage is divided into two facies and difference of sediment types may be one of the principle causes of such differentiation. Comparison of depth ranges of living and empty tests of 95 species shows that some of the tests of almost all species are transported toward deeper water after death. Total population counts are valid in defining the general composition and distribution where little or no displacement of sediment is expected, but generally these counts are not indicative of distribution of living specimens. Maximum abundance of living benthonic Foraminifera occurs between 55 and 150 fathoms and approximately coincides with the greatest number of species and genera. Temperature, food, and sediment type are considered important factors for depth distribution and size of population of living benthonic Foraminifera. Ratios of living to total populations from sediment samples appear to be indicative of the rate of sedimentation. The ratios support the suggestion of Dietz (1952) that sediments from the land are deposited either nearshore or on the lower part of the continental slope and in basins, bypassing the outer shelf and upper continental slope. Rates of sedimentation calculated from an assumed rate of reproduction of Foraminifera are 97 years per centimeter of sediment in the San Diego Trough and 0.36 years per centimeter in the nearshore area. Three methods of calculating the amount of sea-level change by using benthonic Foraminifera are discussed. Five to ten fathoms of deepening is suggested at some time later than the Pleistocene. The presence of shallow-water Foraminifera and Pleistocene Foraminifera in sand layers of a clayey silt core, and in sandy silt on the surface of the floor of the San Diego Trough, where clayey silts usually are found, proves displacement of sediments from shallow to deep water. Siltstones were cored at three stations in and near Loma Sea Valley and Coronado Canyon, and are Miocene in age based on assemblages of Foraminifera, diatoms, and Radiolaria. One hundred and sixty species of benthonic Foraminifera are figured, of which seventy species are discussed as to their ranges of variation of forms and/or synonymies. Two new genera are described: Paradentalina and Recurvoidella; thirty-four new species are described: Ammomarginulina sandiegoensis, Arenoparrella oceanica, Asterigerinata pacifica, Bigenerina hoeglundi, Bolivina peirsonae, B. subargentea, Buccella angulata, Cassidulina bradshawi, C. subcarinata, Cassidulinoides waltoni, Cibicides phlegeri, Cornuspira lajollaensis, Eggerella scrippsi, Epistominella sandiegoensis, Globobulimina hoeglundi, Gyroidina quinqueloba, Haplophragmoides neobradyi, H. Quadratus, Involutina hoeglundi, Karreriella parkerae, Nonion lankfordi, N. parkerae, Nonionella (?) fragilis, Recurvoidella parkerae, Spiroloculina fragilis, Spiroplectammina bathyca, Textularia sandiegoensis, Trochammina chitinosa, T. discorbinoides, T. labiata, T. rhumbleri, Virgulina apertura, V. delicatula, V. sandiegoensis.