Grizzlies are very fast. 56 years ago, I worked in Glacier National Park and we had a bad griz attack on a party of 4; 2 were badly mauled and the third was just mauled on the right leg and back. Fast and strong!!!
little background on this. last fall grandson and i were up north and i stopped on a hill for everybody to take a pee. my dog and him wandered off out of sight. He came back and said there was a lot of "poop" in the trees. I said did it look like a baby ruth. He looked at me funny but said yes. so i went down and took a look, yep, black bear. He had no belt on his pants, wandered out of sight. I told him there was a good and a bad. that was? i said i have more than one grandson and my dog could outrun him, but a bear living there. How do you know that? Well lets see, it's pooping all over the place, there is a rock ledge face for denning not far away, berries on the trees and a water source couple hundred yards away. Does a bear poop in the woods? yes a lot. And a discussion about black bears that normally try to avoid you but then don't. And you are in their front yard. I sent the article to him, i think he got the point. The other thing was i had loaned him a glock that morning, he left it in the glove compartment.
