I received these pictures from a good friend who lives up in Montana. They are pretty amazing. I love big burly animals. The next couple of paragraphs explain where, what and when.
The pictures were taken in Fountain Flats, which is about 10 miles from Old Faithful. The buff-griz encounter is one of the coolest things that I have seen during the 15 years that I have lived in the park.
The pictures appear in chronological order. The bear walked across the road in front of me and started chasing the buffalo herd across the field. Eventually one of the cows challenged the griz and ran him off. The last picture shows how the cow and bear were running in parallel circles around the herd, with the bull on the inside track.
These photos and more can be seen on http://www.yellowstoneecology.com/, which is where the photos oiginated.