city, seat (1899) of Santa Cruz county, southern Arizona, U.S. A port of entry on the Mexican border, it adjoins Heroica Nogales (Nogales) in Sonora, Mexico. Divided by International Avenue, the two communities are together known as Ambos Nogales (Spanish: “Both Nogales”). The city was founded in 1880 by a San Francisco merchant, Jacob Isaacson and called Isaactown. Isaacson built a trading post there, and two years later the Southern Pacific Railroad laid a track there, making the first rail connection between the United States and Mexico. At that time the city was given the name Nogales for its black walnut (nogal) trees. It was the scene of fighting between Pancho Villa (Villa, Pancho)'s forces and U.S. national guardsmen in 1916 and between town militia of the two communities in 1918. Nearby are the Tumacacori Mission National Monument and the ruins of the first white settlements in Arizona. Border trade has encouraged the growth of maquiladoras (maquiladora) in Ambos Nogales, and international commerce is the city's principal economic activity. Inc. 1893. Pop. (1990) 19,489; (2000) 20,878.