In John Schewey's book he recommends crayfish fly patterns, woolly-buggers w/rubber legs, hellgramite patterns. Also match the local hatch if there's a big one (Hexagenia, if you happen to be on a river with a hatch.) Sizes of hooks are roughly size #4, but it varies (2-10.)
Poppers would probably be good in the evenings.
I assume the bigger the fly the bigger the fish it catches, on average.
Clousers good too I bet.
I love ifish.net. I'd also try a SEARCH for "Umpqua" on
www.westfly.com, and you'd probably get more info than you can handle.