containers of low-level radioactive waste were dumped on the continental margin between 1946 and 1970. These drums now litter a large area (1,400 square kilometers) of the sea floor within the marine sanctuary (fig. 2). The exact location of the drums and the potential hazard the drums pose to the environment are unknown. (5) Many faults have been mapped in the Gulf of the Farallones; for example, the San Andreas Fault crosses the Gulf near the Golden Gate Bridge. These faults are a potential seismic risk for the cities in the San Francisco Bay area. (6) Study of the open ocean environment complements ongoing USGS investigations of San Francisco Bay and provides an opportunity to study an estuarine shelf-slope system.

The USGS began this multidisciplinary project by mapping and sampling the continental shelf east of the Farallon Islands. In 1990 the project expanded in scope when the USGS conducted an investigation, sponsored by the USGS, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, U.S. Navy, and National Oceanic and Atmospheric Administration (NOAA), to survey and sample the continental slope west of the Farallon Islands. This cooperative study was designed to provide information about the location and distribution of the drums of low-level radioactive waste and about geologic data on areas being considered as sites for disposal of dredge material from San Francisco Bay.

Data Collection and Results.-A variety of surveying and sampling techniques and technologies are required to sample and measure the many physical products and processes that characterize continental shelf and slope environments. These include but are not limited to geophysical surveys, sediment sampling, bottom photography, and measurements of ocean currents. One valuable surveying tool is sidescan sonar, which allows scientists to characterize the morphology of the sea floor by swath mapping. Sidescan sonar provides an acoustic image, or sonograph, of the sea floor that is similar to a satellite image of the Earth's land surface. As the sidescan sonar instrument is towed behind a ship along previously determined tracklines, the sonar continuously emits pulses of sound that ensonify strips, or swaths, of sea floor. The width of the swaths depends upon the type of sidescan sonar system. Swaths ranged from 200 meters to 5 kilometers in the Farallones study. When constructing a mosaic of the swath images, tracklines are spaced so that adjacent swaths overlap by 10 to 20 percent.

The sidescan data are processed by computers, and a digital gray-scale mosaic of a chosen area of sea floor is progressively built by overlapping and joining adjacent swaths. The shades of gray define the features of the

sea floor and represent varying energy levels of sound returned from the sea floor and, hence, an acoustic image. The differences in the energy of the backscattered sound are related to sediment grain size, surface roughness, hardness, and slope of the sea floor. These sea-floor characteristics reflect the host of geologic processes that have produced the sea-floor environment. The sonographs are used to define the geologic and morphologic setting of the study area, to interpret geologic processes operating on the continental margin, and to provide information relevant to environmental issues.

When information on large areas is required and limited survey time is available, a reconnaissance method is used instead of detailed swath mapping. Data are collected along widely spaced tracklines to obtain an overview of the area. On the continental shelf between Point Reyes and Half Moon Bay, reconnaissance surveys from a high-resolution sidescan sonar system revealed at least four fields of bedforms (ripples and dunes generated by ocean currents). Owing to the widely spaced and non-overlapping sonographs, it was impossible to establish the absolute boundaries and geometric relationships of the bedform fields. Of particular interest were a series of broad (as wide as 2 kilometers), shallow (1-3 meters deep) depressions floored by coarse sand and large wave-generated ripples. To define the pattern and limits of the field of depressions, an 800-square-kilometer area was resurveyed with overlapping swaths and a computer-processed mosaic was constructed on board ship (fig. 1). This study is the first to map and define the field boundaries and thereby establish the geometry and spatial relationships to other shelf features of depressions such as these.

The origin of the depressions is controversial. The intricate pattern of depressions and ripples shows a dynamic and complex sediment transport system that varies with time and space. Information from the mosaic has several practical applications. For example, the evidence of strong currents, as indicated by large ripples in coarse-grained sand, suggests that dredge material and pollutants disposed of at sites on the shelf could be redistributed over large areas. Also, commercial fisherman can use the mosaic to locate substrate preferred by bottom fishes and crabs.

The low-level radioactive waste containers that were dumped in the Farallon Islands Radioactive Waste Dump (FIRWD) may or may not pose a risk to the environment. To evaluate the risk, samples of the sediment, biota, and water must be collected near the concentrations of barrels. However, the exact location of the barrels must be known prior to

sampling. The USGS, in cooperation with NOAA, used sidescan sonar to map two areas within the FIRWD. Total sea-floor coverage was obtained, and computer-processed mosaics were constructed on board ship.

Many small nongeologic targets (barrels) were distributed throughout the survey areas, which covered about 70 square kilometers on the shelf and 125 square kilometers on the slope (fig. 1). Analysis of the sidescan data suggests that many of the targets are 55gallon drums. This interpretation was confirmed at one site by an underwater video and 35-millimeter camera system. Maps of barrel distribution derived from the sonographs are being used to design sampling schemes to evaluate the risk that the levels of radioactivity may have on the biota and environment.

Conclusions.-Geologic Inventory projects such as the Offshore Geology of the Farallones Region are particularly important in ocean areas offshore from major urban centers where human activities have the most impact on the environment and where complex multiple-use decisions are necessary. The data collected during such projects aid in the resolution of geologic and oceanographic questions and critical social problems, such as hazardous waste management and pollution control. Many scientific surveying and sampling techniques, such as the sidescan sonar swath mapping discussed here, are available to help solve environmental problems. Cooperative agency investigations, such as the Farallones Region project, are cost and time efficient. Where feasible, such partnerships can be used to address these important societal and scientific issues.

New State Geologic Maps in New Jersey

By Wayne L. Newell and
Mitchell W. Reynolds

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The USGS and the New Jersey Geological Survey (NJGS), part of the New Jersey Department of Environmental Protection, are completing a new series of geologic maps, which present the distribution and structure of bedrock and earth-surface materials across the State. The cooperative geologic mapping project was begun in 1984. The map information enables Federal and State hydrologists, planners, and engineers to accurately model aquifers, identify other resources, and define strategies for mitigating hazards and targeting resources. The project is one of the initial

geologic mapping projects of the Cooperative Geologic Mapping program element (COGEOMAP) in the National Geologic Mapping Program.

The objective of the National Geologic Mapping Program is to model the geologic framework of the Nation through systematic geologic mapping and analysis of regions. The program provides geologic data necessary to make informed land use planning decisions. Through the COGEOMAP program, State geological surveys and the USGS combine resources to produce geologic maps in areas of mutual interest. During fiscal year 1991, cooperative projects were in progress in 36 States, including New Jersey. Such projects range in scope from quadrangles or counties to entire States and include not only geologic mapping but also geophysical mapping and isotopic and paleontologic geochronology of earth materials. The New Jersey State geologic map project was an early successful model for cooperation between a State agency and the USGS to produce both bedrock and earth-surface materials maps for an entire State.

Two complete maps, one of bedrock and one of surficial geology, provide an overall framework of the geology of New Jersey. Each map includes three panels that portray the north, central, and southern parts of the State at the scale of 1:100,000 (1 centimeter equals 1 kilometer). The bedrock geologic map shows the distribution of (1) Proterozoic metamorphic and igneous rock faulted against Paleozoic cover rock in the State's northern highlands, (2) early Mesozoic basins, which record the initial stages of continental rifting, and (3) a thick, overlapping sequence of unconsolidated late Mesozoic and early Tertiary sand, gravel, and clay, which fill Atlantic Coastal Plain embayments. The surficial geologic map delineates a variable thickness of Pleistocene glacial deposits across the northern part of the State, the weathered regolith on the unglaciated bedrock, and the Miocene to Recent fluvial to marine sediments overlapping older deposits of the Coastal Plain.

The earliest geologic map information for New Jersey was produced by Henry D. Rodgers more than 150 years ago following a brief but comprehensive reconnaissance of the State. Even though the State legislature had recognized early the need for a systematic detailed survey of New Jersey's natural resources, it was not until well after the Civil War that the work was completed with enthusiastic support from the State agricultural society. At the end of the 19th century, a second State geologic map project was initiated using a new, State-surveyed topographic base for geologic field studies. First printed in 1910-12, the map was a forerunner of

modern State geologic maps and has been widely used for 80 years for mineral resources, industrial materials, water resources, and land use planning. The new series of geologic maps, now being prepared for printing, was initiated to provide New Jersey with more reliable geotechnical information to address critical issues concerning water resources, disposal of hazardous wastes, and conflicting interests in land use planning.

Eighty years of progress in geologic research and new uses for geologic information are mandates for compiling new maps. The new State geologic maps are built upon modern concepts, including the collision and rifting of continents, weathering, erosion, the transport and deposition of sediments, climate change, glaciation, and the impact of people on the rates of natural processes. Deep core drilling, seismic profiling, and geophysical maps of the Earth's magnetic and gravitational fields have helped to reliably describe the distribution, shape, and structural configuration of rock types under the surface of New Jersey to depths exceeding several kilometers. This detailed information is essential to understanding the geologic history, the potential for earthquake hazards, and the distribution of resources. Radiometric and paleontologic studies of the ages of the rock units have facilitated the interpretation of the geologic history of New Jersey and aided in such applications as stratigraphic correlations for aquifer modeling.

Beyond the description of rock types and their distribution, the geologic history is an important attribute recorded on geologic maps designed for general-purpose use. Knowledge of the geologic history of New Jersey permits interpretations of the opportunities and limitations presented by geologic processes and environments. Such history permits interpretation of the magnitude and frequency of events such as earthquakes, flooding, climate change, and sea level rise.

Geologic maps and cross sections coupled with an interpretation of the history of geologic processes help map users to predict the suitability of areas for competing land uses. Slope stability, aquifer recharge areas, flood prone areas, eroding coastal areas, and locations along faults can be evaluated using the new geologic maps as a guide. Data from the maps can be computerized and used interactively with other types of spatial data in a GIS to solve many complex earth science problems.

The cooperative project between the USGS and the NJGS has been a pilot for coordinated efforts between State and Federal agencies. The NJGS is responsible for the interpretation of geologic information for

regulating site-specific uses. Realizing a need for more comprehensive map information to fulfill that function, State funds were obtained for the NJGS and the USGS to pursue geologic mapping and basic research in a series of collaborative projects.

The USGS has provided state-of-the-art research skills for geologic mapping. Because the focus of the USGS is national in scope, the collaborative project allows for the geology of New Jersey to be put into a regional perspective across the length and breadth of the Atlantic Coastal Plain, Mesozoic basins, Piedmont, Highlands, and Valley and Ridge provinces of the Appalachians; the project expands the essential national base of geologic information. The NJGS has the detailed knowledge of local geology and extensive archives of information from years of boring for bridges, site investigations, and well logs, which have been essential in developing the overall geologic picture of New Jersey. The involvement of State geologists in the creation and presentation of the new maps ensures that the new geologic data base is most useful and applicable for the NJGS's continuing mandate to apply the information to land use decisions that affect the environment, that provide for responsible use of natural resources, and that impact the well-being of New Jersey citizens.