Yellowstone Bison were easy to find in the Hayden and Lamar Valleys. I had two close encounters with the Bison.
While driving back to the hotel after dark, a Bison walked out into the road, forcing me to swerve into the oncoming lane of the two lane road. Everyone was safe, but it was a close call. It was one of those events that you end up responding to using pure reflex, and end up going over and over again in your head as you fall asleep.
The other encounter was a fun one. While crossing the Yellowstone River bridge into Lamar Valley, a few Bison were blocking the road, so I stopped. While waiting, the few Bison became a herd, who then all crossed the bridge. The bridge shook from all the weight and the Bison herd surrounded my car. It was fantastic to be so up close to the herd from the safety of a car.