plant suggestion to stem bank erosion

Does anyone know of any plants that would be fast to establish
themselves and good at holding soil (gravely clay) on a vertical bank? 
I recently  visited a friend's place in Sonoma county, California, who
asked my advice about a problem with stream erosion next to his access
road.  There is a 12 foot (3 meter) perfectly vertical stream bank that
is gradually eroding at the top, which will eventually wash away the
road. It is in deep shade most of the day, and it is a year round
stream, although not large.  There are a few redwoods (Sequoia
sempirvirens) growing in the vicinity.  I know redwoods would grow
there, but am concerned that if the bank were further undermined
(eventually it has to be, even though the erosion is very gradual, since
it is at the outside of a slight meander) the redwood, when it toppled,
would pull a very large chunk of the top of the bank with it.  I have
seen madrones (Arbutus menziesii) growing on vertical banks, with roots
apparently growing down the surface of the bank, but I wonder that they
might take a very long time to establish themselves.  I have also seen
Paulownias growing along streamsides with massive surface roots.  This
is a climate of heavy winter rains, moderate frosts in winter (28 F),
and little rain from late spring through fall.  There is obviously water
at stream level, but, being 12 feet below, it would take any plant's
roots some time to grow to reach it.  Does anyone have any experience
with these or other trees in such a situation?  Are there any perennial
herbaceous plants that would grow in the vertical clay stream bank? 
Someone once mentioned Hypericum as a bank erosion control (do not know
which species), but I wonder if it would do well in such deep shade.
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