Eagle may be the only city in the arid American West that was first settled on an island. Four young miners left Idaho's gold fields in 1863 to farm what is today called Eagle Island, between the Boise River's north and south channels. Not easily accessed by Indian raiding parties, the island also allowed ready irrigation of the first croplands. It was an island farming couple, Tom and Mary Aiken, that founded the village of Eagle on the north "mainland" starting in 1895. An interurban trolley in 1907 greatly stimulated the growth of the township, which became a service and food processing...