Historical ranges for the "columbian whitetail" deer are from the Mouth of the columbia, to about the Boneville area and inland on both sides for several miles.
The #2 columbian whitetail (Oregon Record book... nwbiggame.com) was killed in the St. Helens / Vernonia area in the 40's. The islands on the columbia still have countable numbers. That #2 buck is on the wall in McLagan's Taxidermy in Bend.
Obviously, Roseburg has a bunch, hench the de-listing and the controlled hunts for the past 2 seasons. The Willamette Valley distribution USED to be from Salem all the way to Medford from what we have discovered in research.
The whitetails you see now in the Ochoco's, Maury's, Wallowa's, Union Co., etc are strains of Eastern Whitetail. They've always been in a few counties in NE OR.
As far as cross breeding, as one could linger down the road to say that the occassional "whitetail" looking deer that we see in the NW area might be a genetic throughback....
There is still debate amongst hunters ,and even some bio's as to whether the Columbian Whitetails cross with Mulies or Blacktails. Some swear by it, others defend the genetic difference.
I can say that from years of antler measuring experience that there is incredible evidence to support characterics of cross-breed in the antlers between Eastern Whitetail and Mulies. However, I honestly don't ever see any apparently cross bread Columbian Whitetail/Blacktails on our Roseburg properties that we hunt and guide on. So who knows.