Summer (June–September) is the high season, with the steam train running daily, rivers in good shape for rafting, and the mountains accessible for hiking. Days are warm, nights cool — Durango is at 6,500 feet — and afternoon thunderstorms are common in July and August.
Autumn is arguably the best season — golden aspens light up the surrounding mountains from mid-September to mid-October, and the crowds have thinned. Winter brings deep snow to Purgatory Mountain, 25 minutes north, and the town slows down but keeps its restaurants and breweries running. Spring is mud season; not the best time to visit unless you are skiing the late snow.