IN THE HIGH SIERRA wilderness country that is the climax of what John Muir liked to call the Range of Light, Wright fell in love with the high world even as Muir had, and each summer brought him closer to its forms, its moods, its tones, its light -- and to the thousand textures that unfolded as the trail turned or as a trailess slope opened up on a broad sweep or an intimate glen that no man had seen before.