In 1867, a man by the name of Jack Swilling stopped to rest his horse at the foot of the north slopes of the White Tank Mountains. He looked down and across the expansive Salt River Valley and his eyes caught the rich gleam of the brown, dry soil turned up by the horse's hooves. He invisioned farm land, predominately free of rocks, and in a place out of reach from heavy frost or snow. Lacking only a water source Jack Swilling came back that year and began digging a canal from the Salt River. By 1911 water flowed freely through the canals thanks to the construction of the Roosevelt Dam. Phoenix's explosive growth began during World War II when many airfields were built in Maricopa County and many defense industries followed. The name Phoenix was chosen because the city was built on the ruins of the Hohokam Indian civilization whose farmers dug irrigation canals still in use today. Phoenix today has a diversified economic base. Manfacturing is a leading employer. Tourism is also an important imcome producer, and Arizona has many world class hotels and resorts. Phoenix's surrounding cities have grown greatly due to it's prosperity. Phoenix, Arizona has become the seventh largest city in the nation. Some of Phoenix's surrounding cities are Mesa, Tempe, Glendale, Scottsdale, and Ahwatukee.