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considered to be on the order of 200 feet (Slade, 1988). Quaternary terrace deposits

capping mesa areas along the Santa Clara River valley are of similar composition as
alluvium, but not considered to be part of the regional aquifer system since they occur above
the regional water table (Slade, 1988).

The Saugus Formation (Figure 12), predominantly consisting of conglomerate, sandstone,

and alluvial deposits, is generally under confined (artesian) conditions within the Eastern
Hydrographic Subunit (Slade, 1988). The maximum thickness of water-bearing Saugus
deposits containing fresh water varies from 1,500 feet to 5,500 feet within this region,
depending on the relative location with respect to faults (specifically, the San Gabriel and
Holser faults).

In a hydrogeologic assessment of the Saugus Formation, Slade (1988) suggested that based
on well log analysis, the Pico Formation underlying Saugus deposits may be fresh-water
bearing south of the Holser and San Gabriel faults. However, the study did not specifically
evaluate the hydrogeology or potential aquifer characteristics of the Pico Formation. In
other areas of the Eastern Hydrographic area, the Pico Formation contains brackish water

and would not be considered a productive or potentially productive aquifer (Slade, 1988).

Sylmar Basin Subarea: Water-bearing deposits within the Sylmar Basin Subarea consist of
Holocene alluvium, older alluvium (Pleistocene-age alluvium and terrace deposits), and the
Saugus Formation (Oakeshott, 1958; Brown, 1975). Holocene alluvium has been derived
from erosion of materials in the San Gabriel and Santa Susana Mountains and is comprised
of unconsolidated fine to very coarse-grained deposits of clay, silt, sand and conglomerate.

These materials vary according to source and proximity of the parent terrane (e.g.,
crystalline basement versus fine-grained sedimentary units), and are on the order of 50 to
60 feet thick. Older alluvium, which is up to 300 to 500 feet thick in the Sylmar Basin
Subarea, is lithologically similar to Holocene alluvium, typically only locally consolidated
(Brown, 1975). The Saugus Formation is a poorly sorted, loosely consolidated conglomerate

and coarse sandstone, with layers and lenses of clay and clayey gravel. The Saugus
Formation is as much as 6,400 feet thick in the Syhnar Basin Subarea (Brown, 1975).

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