Hills of Glass (Glass Mountain)

The Vanishing American:  Once more the character of the slope changed. The solid gleaming granite gave way to soft red sandstone; and the long reaches of ledge and short steps to wide zigzags, the corners of which turned on promontories that sheered out over the depths. Marian found the going easier here, and if she had not been worn out she would have climbed well. As it was she dragged her weary feet, slow step after step, up the long slants of trail. (Chapter VII)

Down Into the Desert: Here came the most danger of the trip. These slopes were smooth and bare and steep. They had to be ascended and descended. Hills of Glass! Our horses followed in our tracks, coming too fast uphill, and stepping very shortly and carefully going down. If a horse slipped he would almost of a certainty knock his leader down a slope.