The horn growth pattern definitely resembles whitetail.I shot a similar deer about 10 years ago in an area of Western WA that is not supposed to contain any whitetails. It was about amile north of Minot Peak near Elmaand in 40+ years of hunting here, no one in my entire family has ever seen a deer that looked like a whitetail other than this one. There is a rumor that years back, someone released some whitetails into the area and they cross-bred with the blacktails.The deer I shot had blacktail marking, but the ears were not exactly right for a backtail and the horns were definitely not right for a blacktail.

You'll have to decide for yourself what you think it is.