Edward Abbey, Desert Solitaire (1968) — not specifically about Tucson, but his account of a season as a ranger at Arches National Park is the foundational book of the modern Southwest. Abbey lived and died near Tucson; he is buried somewhere in the desert here, the exact location kept secret.
Barbara Kingsolver, The Bean Trees (1988) — Kingsolver's debut novel is largely set in Tucson, where she lived for many years. A young woman from Kentucky drives west, ends up in Tucson, becomes the accidental guardian of a Cherokee toddler, and gets entangled in the sanctuary movement that helped Central American refugees in the 1980s.
Charles Bowden, Blue Desert (1986) and Down by the River (2002) — Bowden was Tucson's great writer of the desert, the border, and the violence underneath both. Difficult, brilliant, essential.
Leslie Marmon Silko, Ceremony (1977) — Silko grew up on the Laguna Reservation and now lives outside Tucson. Ceremony is the great Pueblo novel: a young man returns from the Pacific War to find himself and his land both broken.
Luis Alberto Urrea, The Devil's Highway (2004) — a Pulitzer finalist account of fourteen migrants who died trying to cross from Sonora into Arizona through the Cabeza Prieta wilderness in 2001. Urrea makes the desert and the border feel completely real.