On which page of Into the Wild does the quote about "the core of man's spirit" appear?

On page 57 of Into the Wild, Chris McCandless writes, "The very basic core of a man's living spirit is his passion for adventure." He writes this in a letter mailed from South Dakota to his friend Ronald Franz, and, in the letter, he urges Ron to abandon his safe life in Salton City, California and to hit the road in search of adventure. He tells Ron that there is no comfort in a staid and settled life and that he will begin to enjoy a carefree, adventurous existence once he embraces this type of lifestyle. Though Franz was eighty-one years old, he took the advice of McCandless, who was twenty-four at the time. Franz placed his belongings in storage, outfitted his truck with bunks, and hit the road, heading to the desert (to the same campsite where McCandless had stayed).

McCandless had first met Franz in 1992 when Franz was 80, and Franz drove McCandless from Salton City, California, to Grand Junction, Colorado. When Franz was serving overseas in the army, his wife and only child were killed by a drunk driver, and Franz turned to alcohol. It's likely that Franz saw McCandless as a replacement son figure. They became quite close in the time they spent together.