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basin" (Hershey 1902:7). Recent tectonic activity
i
!appears to have created the present southward drainage of

'the upper portion of the basin; there is a strong indica-

,tion that in the past the Piru Creek might have drained

northeastward into the Mojave Desert~ This same tectonic

activity might also explain why there appears to be the

same proportion of slopes facing north as those facing

southe Another possible explanation for the southward

drainage of the basin might be inferred as a rescilt of

faulting activities. The major portion of the basin is

bisected by the northwest trending San Gabriel Fault,

which is a major rift with a large well drained lateral

separation and is further bound in the northeastern part

by the San Andreas Fault, the major structural lineament

of California (Cordova 1956)~

Most of the valley flats along the lower portions of

the Piru Creek are marked along their outtermost rims by

steep mountain walls which give way to intermittenly

gentle slopes and level open benches, these in turn drop

dovm steep embankments t:o the floor of the Piru Creek's

channel. The level areas of most of the benches and

valley flats vary in size between the upper and lower

portions of the basin, however, most are alike in that

they are covered by shallow, irregular stony soils formed

in place by residual weathering of the thick sedimentary

sequences. Typical of these soils is an Altamont Loam,