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City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
wave-cut platform correlated by the majority of geologists with the Bay Point Formation, and by
others with the Nestor Terrace, and are believed to be approximately 120,000 years old. Gaal
and Kuhn (1985) pointed out that the age and correlation of this terrace are controversial and
need to be determined by detailed mapping and dating techniques.
The published regional geologic maps show these deposits as undifferentiated marine and non-
marine (colluvial), poorly consolidated deposits of late the Pleistocene-age (120,000 years old)
Bay Point Formation composed of pale to reddish brown, fine- to medium-grained fossiliferous
silty sandstone (Kennedy, 1975). Kuhn (1977) differentiates between basal marine deposits,
which he describes as unconsolidated, laminated beach sands with pockets of fossil shell
debris, and overlying non-marine deposits varying horizontally from wind deposited dune sands
to alluvial sands and vertically to cemented soils (discussed below).
"Beach Ridge" Type Deposits
Iron oxide-cemented "beach ridge" residual clayey sand deposits may be observed in the upper
bluff capping marine terrace deposits in several parts of Solana Beach. They were described
during the field investigation by Group Delta (1998), and believed to be formed during a period
of tropical to temperate climate associated with increased surface weathering, leaching, and
precipitation of salts and minerals.
Gaal and Kuhn (1985) indicated that these deposits were locally overlain by sand dune deposits
and soil zones, also locally cemented with iron oxide. Sand dunes could be observed on 1954
aerial photographs adjacent to farmlands, but were removed following the residential
development in the 1970s.
Landslide Deposits
Landslides and blockfalls are two main types of the gravity-induced processes modifying the
Solana Beach coastline. The occurrences of landslide and blockfall deposits are greatly related
to the distribution of structural discontinuities (e.g., bedding planes, joints, faults). Landslide
deposits in the study area are primarily rotational slump deposits associated with marine terrace
deposits of the upper bluff. The blockfalls are typical of both the lower seacliff (rockfalls) and
upper bluff. These deposits are episodical and may only be observed for a short period of time
before they get washed offshore or redeposited as beach sediment.  In July 2001, an
approximately 100-foot-long blockfall of the lower bluff was observed in the area below
245 Pacific Avenue. Two areas of recent failures in the upper bluff material were observed
below 327 and 357 Pacific Avenue in October 2001.
Beach Deposits
The modern beach deposits consist of unconsolidated silt, sand, and gravel. In July 2001,
beach sand was placed on the beach from dredging operations as part of the 2001 San Diego
Regional Beach Sand Project (SANDAG, 2000b). Shingle (gravel) beach was observed during
the site reconnaissance from Seascape Surf (567 South Sierra Avenue) to Del Mar Shores
Project No. 323530000
Page 3-9






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