After "years on years" of working "their way through the high meadows and mountain drainages, horse-packing into the Big Horns, Medicine Bows, south end of the Gallatins, Absarokas, Granites, Owl Creeks, the Bridger-Teton Range, the Freezeouts and the Shirleys, Ferrises and the Rattlesnakes, Salt River Range, into the Wind Rivers over and again, the Sierra Madres, Gros Ventres, the Washakies, Laramies, " Jack found it hard to remain equanimous when he discovered that even that life was getting harder to schedule.
def - Of an even, composed frame of mind; of a steady temper; not easily elated or depressed.