The Monterey deep-sea fan is an arcuate wedge of sediment that occupies 100, 000 square kilometers of the floor of the Pacific Ocean at the base of the continental shelf off the coast of central : .:. California. The slope of the fan surface gently decreases radially from an axerage 6f 28' at the apex of the fan, at a depth of 3000 meters, to an average of 07' at the outer edge of the fan, at depths about 4500 meters. Two parallel submarine channels (Ascension and Monterey east), which flow respectively out of the mouths of the Ascension and Monterey canyons, cut into the smooth surface of the fan and extend approximately 300 kilometers to the outer edge of the fan. Hydraulic functions (Leopold and Maddock, 1953) calculated for these channels O. 38, (2) D = 0. 39 Q 0. 34 are: (1) W = 17. 3 Q 0. 26 , and (3) V = 0.19 Q . The hydraulic functions indicate that the energy of the current, which ' forms the channel, is concentrated at the base of the current. Bankfull mean velocities calculated from a modified Chezy-Manning equation (Hurley, 1964) decrease downstream from about 8. 5 meters per second, near the apex of the fan, to 1. 0 meters per second at the outer margin of the fan.

Turbidity currents, which flow down the submarine canyons and out the submarine channels, seem to be the major agency for transporting 'material to, and distributing material on the fan. The hydraulic functions suggest that thin- dense currents (Stoneley, 1957) carve the channels. Thick, relatively les s dense currents (Plapp and Mitchell, 1960) that are subject to lateral spreading may distribute sediment to regions away from the submarine channels. Repeated migrations of the submarine channels, analogous to the migrations of stream channels on alluvial fans, resulting in the shift of the areas of maximum deposition probably produce the half- cone shape of the Monterey fan. Low velocity bottom currents of undetermined origin probably play a minor role in redistributing sediments and modifying the shape and surface of the fan.

Forty- six gravity cores and three piston cores of sediments from the upper surface of the Monterey fan and adjacent regions are the primary sources of data for lithologic and mineralogic studies of the fan. The sediments from the surface of the fan are chiefly green-gray mud (silt and finer material) occasionally interbedded with thin (approximately one to two centimeters) dark very fine sand layers, which have a muddy matrix. Cores taken near the submarine channels generally have sediment that is coarser and contains a higher percentage of sand than sediment taken at a distance from the channels. BP 10, a core from the Monterey east channel 274 kilometers from the head of the Monterey canyon, has a 1. 8 meter thfck. unit of a poorly sorted mixture of pebbles, granules, sand and mud, with pebbles up to 50 millimeters long.

The light mineral suite of the sand fraction is characterized by a low quartz-feldspar ratio, and high mica and altered rock fragment content. The heavy mineral suite of the sand fraction consists chiefly of green and brown hornblende, "cockscomb" pyroxene, chlorite, and manganese coated rock fragments. The composition and immature aspect of the sand fraction and the high content of mud matrix in the sand layers indicate that most of the sands on the Monterey deep-sea fan are the modern equivalents of graywackes.

The heavy mineralogy of the sand fraction for beach samples reported by Sayles (1966) and 10 new offshore samples from South Monterey Bay was determined optically. For each sample the percentage of the more diagnostic transparent minerals is plotted graphically in order of persistence: zircon, garnet, biotite, apatite, clinozoisite and epidote, lawsonite, green hornblende, oxy-hornblende, glaucophane, sphene, zoisite, augite, jadeite, hypersthene, enstatite, and tremolite & actinolite. Additional data on accessory transparent minerals, composite grains (rock fragments) and opaque minerals are listed with each graph. An updated bibliography is presented to include all new work on the geology and sediment of Monterey Bay.

The following work is part of a continuing study of the sediments and sedimentary processes of the continental shelf of central Califor nia done in cooperation between the University of California, Berkeley, and the Coastal Engineering Research Center, U. S. Army Corps of Engineers. Sediment analyses of the samples were done at the Univer sity of California, Berkeley, utilizing the facilities of the Depart ments of Civil Engineering and Geology and the Institute of Marine Resources. The results of this study will be presented in three separate reports:

Part A Introduction and Grain Size Data (this volume) Part B Mineralogical Data Part C Interpretation and Summary of Results

The first two reports, Parts A and B, will be presented with little or no interpretation. In Part C the authors' interpretation of the data plus background information and previous work in the study area will be given.

The area covered by this report extends from Pigeon Point in the north to Sand Hill Point in the south. With the completion of this report a complete section of the continental shelf of California from Russian River to Monterey Bay will have been studied. The methods of sediment analysis employed in the overall study are grain size analysis followed by heavy mineral analysis and interpretation.

The following work is part of a long term study of sediment trans port on the Continental Shelf of Central California. In particular, it is hoped that the data presented here will be useful also to the general study of the factors that influence the natural environment of Bolinas Lagoon now being conducted as a cooperative effort involving the University of California, Berkeley; the U. S. Corps of Engineers; the U.S. Geological Survey; the Department of Agriculture, Soil Conservation Service; and consultants for the Bolinas Harbor District.

The analyses of the marine sediments of Bolinas Bay were done at the University of California, Berkeley, utilizing the facilities of the Departments of Civil Engineering and Geology and the Institute of Marine Resources. The results of the marine study will be presented in three separate volumes:

Part A — Introduction and Grain Size Data Part B — Mineralogical Data Part C — Interpretation and Summary of Results

Grain s i z e , heavy mineral, and o r g a n i c c o n t e n t a n a l y s e s of 43 marine and 9 i n t e r t i d a l and f l u v i a l samples p l u s d a t a from 28 marine samples from a previous study by Sayles (1965) form the d a t a i n t e r p r e t a t e d in t h i s r e p o r t f o r the area landward of 90 meters depth (50 fathoms) from P i l l a r Point t o Pigeon P o i n t , C a l i f o r n i a , between t h e Golden Gate and Monterey Bay.

This study i n d i c a t e s : ( 1 ) ' The grain s i z e of t h e sediment decrease off shore except f o r a nose of c o a r s e r sediment from -36 t o -50 meters extending from the north t o the l a t i t u d e of Half Moon Bay. (2) The heavy mineralogy is dominated by hornblende w i t h v a r y i n g amounts of a u g i t e and hypersthene. F r a n c i s c i a n m i n e r a l s a r e found only i n t r a c e amounts. (3) Three major source areas f o r t h e s u r f a c e sediment a r e apparent (a) a great v a l l e y- Sierran source r e l a t e d t o the sediments of t h e present San Francisco o f f s h o r e b a r ; (b) a l o c a l source r e l a t e d t o the drainage basins now emptying d i r e c t l y i n t o the area off s h o r e ; (c) a q u a r t z d i o r i t e source presumably montara t o t h e north. (4) The major d i s t r i b u t i o n p a t t e r n of the sediment may be explained (A) from -90 t o -20 meters by the superimposition o f l o c a l stream drainage on the s h e l f on r e l i c t sediment from the north during lower stands of sea l e v e l w i t h l i m i t e d reworking and mixing of sediments a t province boundaries during t h e l a s t rapid r i s e of sea l e v e l ; and from -20 meter t o present sea l e v e l by p a r t i a l homogenation of l o c a l sediment during a slow rise i n sea l e v e l .

17 of intertidal and stream samples from Monterey Bay - Point Sur Area are analysed for grain size properties. These samples were taken to provide source area information for the study of the offshore sediments of the Central California Continental Shelf. The data are presented graphically as cumulative weight percent curves and histograms with respect to grain size. The statistical parameters median~ sorting coefficient, skewness and kurtosis are calculated for each sample.

The heavy mineralogy of the sand fraction for 44 offshore, 9 beach, and 3 stream samples for this region is determined optically. For each sample the percentage of the more abundant or more diagnostic transparent minerals is plotted graphically in order of persistence and additional data on accessory transparent minerals, opaques, and composite grains (rock fragments) are listed.