I came across natureserve.org and found some very interesting data presented by them with regards to biodiversity across the United States. They had couple tables ranking the states such as the top-ranking states when it came to diversity and states ranked with regards to levels of rarity and risk. Oregon is listed as number 2 and Washington as number 4 on the risk table for amphibians interestingly.
Looking at the table for top-ranking states in diversity Oregon is in the top 5 with regards to plants and mammals but something else pretty striking is that Oregon is located in 8th place in the very last table of this document that lists all 50 states in terms of the # of species present.
Take a look here for the full ranking a more information: http://www.natureserve.org/library/stateofunions.pdf