Bison and Mormon Row Barn, Grand Teton National Park

Bison are very large (up to 2,000 lbs) and can be very dangerous. I was not far away from this heard of about 50 Bison, but there was a barbed wire fence between us. I was comfortable with them getting as close as about 20' from me. The heard was filing through an opening in the fence about 100 yards/meters away and out into a vast Sage Brush plain. I was busy shooting and enjoying nature when I heard a deep grunt close behind me. I turned to see a large bull coming around my SUV. I quickly went the other way and jumped in the passenger door - and shot from inside the balance of my time there.
 
In this shot, a lone bull approaches a bull tending a cow.