Rio Arriba County, New Mexico: History
The county was one of nine originally created for the Territory of New Mexico in 1852. Originally extending west to the California line, it included the site of present-day Las Vegas, Nevada. The county seat was initially sited at San Pedro de Chamita, and shortly afterwards at Los Luceros. In 1860 the seat was moved to Plaza del Alcalde. Since 1880 Tierra Amarilla has been the county seat.
The Battle of Embudo Pass took place in the southern part of the county during the Mexican–American War in January 1847.