By the 17th century Father Kino named the river Santa Cruz which means “Sacred Cross” in Spanish. The length of the Santa Cruz River is approximately 184 miles (296 km) long. The river flows southward from the San Rafael Valley to Mexico then reenters the United States just east of Nogales, Arizona. The Santa Cruz River continues northward from the international border, parallel to the I-19 corridor, past Rio Rico, Tumacacori, Tubac, Green Valley, Sahuarita, Tucson, Marana, and Picacho Peak. The Santa Cruz River goes underground south of Casa Grande and meets with the Gila River.