3.5 Cultural Resources
SO-9
The dredge area footprint covers a complex but elongate-shaped region, oriented with its long axis in a
beach-parallel direction (4,000 feet) and with its short axis beach-perpendicular and of varying width
(1,000 to 1,500 feet). The water depth varies from 45 feet along the northeast edge to 58 feet along the
southwest edge. A maximum dredging depth of 10 feet below the sea floor is proposed. The geophysical
survey data collected at this site cover approximately 90 percent of the dredge site footprint. Geophysical
data were collected on two occasions. In January 1999 a survey grid with both side-scan sonar and sub-
bottom profiling was collected, consisting of four survey lines perpendicular to the beach direction, and
eleven survey lines parallel to the beach direction. A total of 12 vibracores were also collected, primarily
in the northeast portion ofthe borrow site, and five of these vibracores fall within the proposed dredge area.
The deepest core penetration was 17 feet, occurring in the northern portion of the grid. During a previous
beach replenishment study conducted by the Army Corps of Engineers (1993) three additional cores were
collected in the presently proposed sand dredging site. In January 2000, additional side-scan sonar data
were collected in a rectangular region overlapping and slightly shoreward of the previous survey grid.
Geoarchaeological Results
According to recent search results conducted for the proposed project, no prehistoric offshore
archeological sites have yet been recorded in or near this borrow site. Based on available data, the SO-9
area is located along the southern margin of the offshore paleochannel of the Santa Margarita River, near
its junction with the offshore paleochannel of the San Luis Rey River. The side scan sonar data collected
for the present study (Sea Surveyor 1999) reveal a smooth featureless bottom texture at SO-9, suggesting
that silt rather than sand is the dominate surface sediment. The sub-bottom profiles reveal a complex
stratigraphy, with a prominent paleochannel oriented perpendicular to the current shoreline. At the bottom
of the profile are pre-transgression fluvial sediments at depths of 10 to 17 feet. Overlying are intertidal,
lagoonal and offshore sediments to the west and only intertidal and offshore sediments to the east.
Evidence for the fluvial sediments is the presence of gravel and other coarse sand near the bottom of
several cores. Likewise, evidence for the intertidal, lagoonal, and offshore environments comes from the
presence of diagnostic shells.
The potential for occurrence of archaeological sites within SO-9 grid appears to be high. The location is
ideal for prehistoric settlement: at the junction of two river channels near the shore. Site preservation may
be problematic, however, since cultural materials would be present within fluvial sediments, the uppermost
Regional Beach Sand Project EIR/EA
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