When I lived in Tucson a few years back, I often wondered why a city even existed there. Modern Tucson is completely dry, save a few artificial ponds propped up for the golfing set. The few desert washes that pass through town are bare sand most of the time, filling only briefly during the heaviest monsoon rains. It's not the sort of place any sane person would think to plant a city.
Yet, historical photographs of the area tell the true story. Photographic archives are a tremendous resource for anyone with an interest in how landscapes change. Old Tucson, it turns out, was founded on the banks of the permanently flowing Santa Cruz river, nestled in the shade of cottonwood trees. Only with development was the river pumped into a memory.