Although some of the specifics are different, I think you are likely remembering the conclusion of Black Elk Speaks, which is presented as the as-told-to autobiography of Nicholas Black Elk, a spiritual leader of the Lakota nation.
I did not know then how much was ended. When I look back now from this
high hill of my old age, I can still see the butchered women and children lying
heaped and scattered all along the crooked gulch as plain as when I saw them
with eyes still young. And I can see that something else died there in the bloody
mud, and was buried in the blizzard. A people’s dream died there. It was a
And I, to whom so great a vision was given in my youth,—you see me now a
pitiful old man who has done nothing, for the nation’s hoop is broken and
scattered. There is no center any longer, and the sacred tree is dead.
In context, the quote was indeed spoken as a reaction to Wounded Knee, and (currently) appears on this Wikipedia page, https://en.wikipedia.org/wiki/Wounded_Knee_Massacre, making it more likely it was the one you saw. I thought at first you might have conflated several quotes, but I didn't see ones specifically referencing animals and "loneliness."