In early August, Bob Bennett and I left the parking lot at about 6:00 a.m. to hike west into the Hayden Valley past Sulfur Mountain. We planned to watch the bison activity in the back country and have a nice long hike through the open, rolling sagebrush and grassland stretching for miles to the west toward Mary Mountain. About one and a half miles in we came upon a small herd of about 25 bison cows and calves. We stopped about 300 yards from them and watched for a few minutes. They were pretty quiet; so I changed direction a little to go around them. We walked 50 yards or so over a small rise and to our left about 60 yards away I saw a bison bull carcass lying in the sage. The feet were extended toward us, and the carcass was still nearly intact. I stopped and pointed it out to Bob, who had a pair of binoculars. He wasn’t familiar with using them, and while I speculated that the bull may have been killed by another bull during the rut, he found the bison in his binoculars. We were not going any closer since we were in bear country. Many times a bear will claim a carcass, and when it is not actively feeding, it will lie nearby to protect it from other scavengers. I did not see any sign of a bear from our perspective 60 yards away. After a couple of minutes we started to walk to the southwest in the same line of travel in which we were originally going, which would take us away from the carcass past the small bison herd. After taking about six steps I saw a grizzly bear’s head pop up between the legs of the bison carcass. It was looking toward the belly of the bison, so it didn’t see us. I pointed to the bear and said quietly, “Bob, we gotta get out of here.” He started to look with his binoculars, and I said, “No, we gotta get out of here.” I now went west directly away from the bear and toward the small bison herd. I was going to use them as a shield from the bear if I could get to them. Watching over my shoulder I could see the bear had not seen us as we started for the bison herd. Again Bob stopped and turned to look with his binoculars, I immediately stepped back to him and told him to stop looking and follow me. We walked only about fifty more yards from where we had first seen the bear when it saw us, jumped up, and started to run around the carcass throwing dirt on it, becoming very agitated. I decided we should look as non-threatening as possible so I stopped, set my tripod and 700 mm lens down and kneeled behind it. Bob kneeled right beside me. We didn’t say much, but I was thinking, “This is going to hurt.” Shortly after we had kneeled down, I realized this was a female bear because she woke up her three cubs of the year. Now I knew it was even more serious because the most dangerous time to be near a bear is when she has cubs or when she has a carcass. This had some sort of geometric increase in risk. The sow stood on her hind legs a couple of times to get a better look at us and swung her body back and forth, huffing and popping her jaws, which meant she was upset and warning us away. Maybe we should have stood up again and walked away some more, but I wanted to continue to be as non-threatening as possible. While I was waiting to see if this really was going to hurt, I made a couple of photographs. About eight seconds after I made this photograph, she dropped onto all four feet and charged us, running straight at us as fast as she could through the sage, the three little cubs running after her, trying to keep up. When she started towards us, I stood up, now to look as big as I could. Bob stayed right beside me. When she started toward us, I planned to stand my ground and if she got within 50 yards, raise my arms in the air and look as tall as I could, and if she was still coming at 10 yards away, to drop to the ground, curl up in a ball with my knees up to my stomach to protect my belly and my hands behind my neck to protect my spine, and hope she chewed on Bob. She was running very fast, but it seemed as though things were happening in slow motion at the same time. She got about 50 yards away from us and then spun around, running over her three cubs, and headed straight back towards the carcass. The three cubs scrambled up and took off after her again. They ran past the carcass and off to the east up a hill about an eighth of a mile away and over it out of sight. I don’t think I breathed until she had disappeared, and I knew I was going to live. Bob and I exchanged words of relief and after a couple of minutes walked on to the south west around the small bison herd. At lunch, after we had thought about our experience while hiking through the valley, Bob asked me, “What would you have done if I hadn’t been there?” I said, “I would have gotten farther away,” because I wouldn’t have stopped to look through binoculars before she saw me. I don’t know if I would have reached the bison herd, if I had been on my own. If I had been there alone, I would have looked a lot smaller than I did with Bob standing right beside me.