The Zapotecs (Zoogocho Zapotec: Didxažoŋ) are an indigenous people of Mexico. The population is concentrated in the southern state of Oaxaca, but Zapotec communities exist in neighboring states, as well. The present-day population is estimated at approximately 800,000 to 1,000,000 persons, many of whom are monolingual in one of the native Zapotec languages and dialects. In pre-Columbian times, the Zapotec civilization was one of the highly developed cultures of Mesoamerica, which, among other things, included a system of writing. Many people of Zapotec ancestry have emigrated to the United States over several decades, and they maintain their own social organizations in the Los Angeles and Central Valley areas of California. There are four basic groups of Zapotecs: the , who live in the southern Isthmus of Tehuantepec, the , who live in the northern mountains of the Sierra Madre de Oaxaca, the southern Zapotecs, who live in the southern mountains of the Sierra Sur, and the Central Valley Zapotecs, who live in and around the Valley of Oaxaca.