It sounds like a six gill from the description, and the proximity to the Canyon makes it plausible - according to a reference book I have, they are believed to undertake nightly "vertical migrations" into shallower water for feeding. This is typically seen in areas where deep water abuts shallower water (like Monterey, Puget Sound, etc).
Very cool sighting!
I've had seven gill sharks steal fish from my stringer while fishing the kelp beds during the day (including chomping off a 35" WSB right behind the gills in one bite), and that is scary enough - I can only imagine having it happen at night repeatedly!
