Building: Homes on the Range

San Francisco Merchant James Ir vine could hardly have reckoned the size of the legacy he set up back in the 1880s, when he wove three Spanish land grants into a single parcel of Southern California countryside. Rolling 22 miles inland from the Pacific coast, his Irvine Ranch has remained virtually intact as an 83,000-acre spread, nearly six times the size of Manhattan.

Originally devoted to sheep and cattle, over the years the land has been turned to farming (barley, potatoes, wheat) and later to citrus on a vast scale. The real crop...