The history of Arizona encompasses the Paleo-Indian, Archaic, Post-Archaic, Spanish, Mexican, and American periods. About 10,000 to 12,000 years ago, Paleo-Indians settled in what is now Arizona. A few thousand years ago, the Ancestral Puebloan, the Hohokam, the Mogollon and the Sinagua cultures inhabited the state. However, all of these civilizations mysteriously disappeared from the region in the 15th and 16th centuries. Today, countless ancient ruins can be found in Arizona. Arizona was part of the state of Sonora, Mexico from 1822, but the settled population was small. In 1848, under the terms of the Mexican Cession the United States took possession of Arizona above the Gila River after the Mexican War, and became part of the Territory of New Mexico. By means of the Gadsden Purchase, the United States secured the northern part of the state of Sonora, which is now Arizona south of the Gila River in 1854. In 1863, Arizona was split off from the Territory of New Mexico to form the Arizona Territory. The remoteness of the region was eased by the arrival of railroads in 1880. Arizona became a state in 1912 but was primarily rural with an economy based on cattle, cotton, citrus, and copper. Dramatic growth came after 1945, as retirees and young families who appreciated the warm weather and low costs emigrated from the Northeast and Midwest. In the Mexican–American War, the garrison commander avoided conflict with Lieutenant Colonel Cooke and the Mormon Battalion, withdrawing while the Americans marched through the town on their way to California. In the Treaty of Guadalupe Hidalgo (1848), Mexico ceded to the U.S. the northern 70% of modern-day Arizona above the Sonora border along the Gila River. During the California Gold Rush, an upwards of 50,000 people traveled through on the Southern Emigrant Trail pioneered by Cooke, to reach the gold fields in 1849. The Pima Villages often sold fresh food and provided relief to distressed travelers among this throng and to others in subsequent years. Paleo-Indian period Paleo-Indians settled what is now Arizona around 10,000 to 12,000 years ago. According to most archaeologists, the Paleo-Indians initially followed herds of big game—megafauna such as mammoths, mastodons, and bison—into North America. The traveling groups also collected and utilized a wide variety of smaller game animals, fish, and a wide variety of plants. These people were likely characterized by highly mobile bands of approximately 20 or 50 members