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Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 5
It should also be noted that the depression in the coastal bluff in this area, i.e.,
within the upper terrace surface, represents an excavation made in the late 1920s to
provide a visual and recreational amenity in this North County community, and is
not of geologic or geomorphic origin. Prior to the excavation, however, this area
did originally drain to the coastal bluff, with its small upland watershed extending
easterly to Pacific Coast Highway.
2.1.3 Groundwater
Although limited amounts of groundwater likely exit the coastal bluffs in this area,
the topographic relief, with upwards of 20 feet of fall from the coastal bluff to Pacific
Coast Highway, and then ample gradient to San Elijo Lagoon to the north and
Fletcher Cove to the south, likely limits the volume of initial infiltration as a
groundwater source. Additionally, unlike the more impervious Eocene formations
further north, the underlying Torrey Sandstone does not create an impermeable
perching horizon, which would encourage groundwater to exit the bluff face along
the contact between the coastal terrace deposits and the underlying cliff-forming
Eocene-age formation. Although surfacing groundwater is often a problem within
other North County coastal areas, the Solana Beach coastline appears to be
relatively immune to this subaerial process, with the possible exception of the
Pleistocene fluvial deposits underlying Fletcher Cove.  Typical sources of
groundwater would include: 1) natural groundwater migration from highland areas
to the east of the terrace, and 2) infiltration of the terrace surface by rainfall, and by
agricultural and residential irrigation waster (Turner, 1981). During our field
investigative work, groundwater was only observed at the back of the sea cave below
205 Pacific Avenue and along the Pleistocene contact within Fletcher Cove, where it
may have contributed to the increased differential marine erosion in this area.
2.2
Geologic Structure
The geologic structure of the Solana Beach coastline is the result of faulting and folding in
the current tectonic regime, which began approximately 5,000,000 years ago when the
Gulf of California began to open in association with renewed movement on the San
Andreas fault system (Fisher and Mills, 1991). The nearest member of the fault system is



 


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