"Muir was racist. It's all right there in his own writing" is the only quote highlighted on the back cover of this book. I picked it up cautiously, ready to have yet another admirable historical figure become tainted.
But though this quote comes from the foreword, though it's highlighted so prominently, it doesn't seem well-supported to me. He certainly doesn't consider native people to be "Noble Savages" entirely above reproach as is fashionable in many quarters, but nothing in this volume (claiming to compile his worst writings) indicates racism.
Of negroes (as everyone called them at the time, as Booker T Washington called them, as Martin Luther King called them). He rides a while with an old negro man, and after a short description of their conversation comments "Many of these Kentucky Negroes are shrewd and intelligent, and when warmed upon a subject that interests them, are eloquent in no mean degree." Given that this story takes place only shortly after the Civil War (which his conversational partner lived through), I think it's fair to say that Muir's attitudes were ahead of his time, and quite acceptable by even strict modern standards.
Of the Eskimo: "They are better behaved than white men, not half so greedy, shameless, or dishonest... These people inspire me greatly, and it is worth coming far to know them, however slightly... But there was a response in their eyes which made you feel that they are your very brothers." If we grade on a curve remembering that Muir was writing in a much more racist time, this is truly impressively not-racist. If we don't grade on a curve, this is still better than the vast majority of us moderns seem to do on race relations.
Outside the question of racism, I'd say the book was good but not great. I learned that before his life as a conservationist, Muir was an inventor, and a rather prodigious one at that. I also finally read his account of climbing a great tree during a windstorm, an essay I've heard described secondhand several times and was delighted to find the original even more compelling. His theories on the glacial formation of the steep valleys of the high Sierra were I think fairly innovative at the time, and have since been vindicated.