My First Summer in the Sierra presents Muir's journal entries from his first long-term adventure in Yosemite and the surrounding area, when he helped drive a flock of sheep through the foothills toward the headwaters of the Merced and Tuolumne Rivers. Muir's vivid descriptions of nature are infused with his characteristic wonder at the magnificence of wilderness, from a single lily "worth going hungry and footsore endless miles to see" to a vista of the luminous Range of Light.