Can someone please help me out on this subject. I have seen this explained by so many people in many different ways. Yes, I know that I5 in California is the cut off for the true Blacktail and the so called crosses. What I am looking for is real hard DNA proof in a published journal of sicence that the Blacktail and Mule deer are two different spicies. From what I have found, no one has done a study to prove that the deer in the Sierra Nevada foothills are a cross. If you can please provide a link, I would love to read about it.