Hey Richard, I don't fish the Kern much, but I have been known to be forced into tying on a piece of sin to the end of my dry from time to time. It works particularly well in the early AM when the fish haven't quite started looking up.
On the local water I can sometimes get away with a #18 dry and will use a #16 if the water is faster. I'd imagine this would also work on parts of the Kern, but you may have to up size.
In terms of preferred pattern, my choice would be a hi-vis EHC (just an EHC with a bit of hi-vis shuck placed over the elk hair). This provides a good compromise of see-able fly and also eatable fly.
If the fish aren't picky, you can throw on your biggest stimi or hopper or even a thingamahopper, but this may not be very productive on certain water. If the fish are not eating caddis type stuff, then I would go with a large parachute gnat with hi-vis coloring on the post. Basically, something that has a parachute post for hi-vis, but also has hackle wrapped around the body for more floatatiousness.
This one I didn't seem to parachute, but you get the idea...