DESCRIPTION: “Help Keep Slab City Clean.” The Imperial Valley still attracts migrants, and not just agricultural laborers. Slab City is an informal desert settlement whose population swells with snowbirds in the winter then dwindles to a few year-round residents in the summer. Concrete slabs, remnants of a former WW II training ground, provide platforms for trailers, trucks, and makeshift dwellings, somewhat like the migrant squatter settlements Lange photographed. The site abuts a military bombing range.