The American Southwest—Arizona and New Mexico, plus parts of California, Colorado, Nevada, Texas and Utah—is at once the oldest and newest part of the contiguous United States. Francisco Vasquez de Coronado explored Arizona and New Mexico in 1540, 25 years before his fellow Spaniards established St. Augustine, Fla. Santa Fe, NM, was founded in 1610, a decade before the Pilgrims landed at Plymouth Rock. Yet New Mexico and Arizona—designated the 47th and 48th states in 1912—were the last stars added to the American flag before Alaska and Hawaii. This is the land of the "Old West," where gunslingers from Wyatt Earp to Billy the Kid blazed into legend. Yet it's also where, at Alamagordo, NM, the atomic age was born. Whether your ancestors settled here in Spanish times or came and went with the more recent mining and casino booms, read on to rustle up your Southwestern roots.

Bordered Up
To know where to look for Southwestern ancestors, you'll need a little history. Boundaries in this wide-open country shifted like the desert dunes: Parts of Nevada, for example, once belonged to Arizona, Utah and New Mexico. Western Texas has flown the flags of Spain, Mexico, the Republic of Texas and the Confederate States.

The first Spanish settlements fanned out slowly from the El Paso, Texas, area in the 17th centuray. A Pueblo Indian revolt in 1680 impeded colonization of present-day New Mexico, but the Spanish resettled there by 1693. Penetration into more-remote parts of the Southwest happened more slowly—in Arizona, just the area around Tucson was settled initially. Then in 1821, with Mexican autonomy from Spain, the Spanish settlements in the Southwest briefly became part of the young nation of Mexico.

Mexican dominion over the Southwest began to crumble with Texas' declaration of independence in 1836, then it collapsed after the Mexican-American War. In 1848, the Treaty of Guadalupe Hidalgo ended the war and fixed the US-Mexico boundary at the Rio Grande, the Gila River and the Colorado River. For $15 million, Mexico ceded almost half of its territory, including most of today's New Mexico, Arizona, Colorado, Utah and Nevada, plus California. The 1853 Gadsden Purchase added the rest of southern Arizona and southwestern New Mexico.

Brigham Young, who'd arrived in Utah in 1847, had hisown ideas for the new territory&3151and then some. He and his Mormon faithful dreamed of a state of Deseret that would span Utah, parts of Idaho and Wyoming, and a swath from northern New Mexico and Arizona west to Carson City, Nev., and San Bernardino, Calif.

But the Compromise of 1850 nixed that idea, dividing most of the United States' vast southwestern holdings between the New Mexico Territry, which covered today's New Mexico, Arizona, part of Colorado and the southern tip of Nevada, and a more modest Utah Territory. Besides present-day Utah, it encompassed the rest of Nevada, the western third of Colorado and a corner of Wyoming.

The lure of silver quickly changed that map. The 1859 discovery of the Comstock Lode in Nevada turned that section of the Southwest into a series of boomtowns, attracting adventurers of all stripes, including Mark Twain. Nevada became a separate territory in 1861 and a state in 1864, long before its neighbors. Arizona, which spun off into its own territory in 1863, gave up what had been Pah-Ute County to Nevada in 1866.

The spread-out Southwest states may surprise you with how few counties they contain. Daniela Moneta, genealogy librarian for the Arizona State Library, Archives and Public Records, notes of her state, "Geographically, it is quite large and there are only 15 counties. Several Rhode Islands would fit into one of its counties. This makes travel from one county to the next very time-consuming, especially if you want to visit the historical societies and the county courthouses."