The northern part of Mexico, ir El Norte, including Chihuahua, Coahuila, Durango, Nuevo León, Sinaloa, Sonora and Tamaulipas, is the home of most of the foods that the rest of the world considers to be Mexican, including burritos, nachos and fajitas. Northern Mexico is divided from the rest of the country by deserts and marshes, which prevented the Azrtecs moving this far north, while the mountains of the Sierra Madre Occidental and the Sierra Madre Oriental contain a vast, semi-arid plateau of grassland. The indigenous people were mainly nomadic, searching for food where they could find it and taking their flocks with them. Roast goat is a popular dish as is roast beef as beef cattle thrive in the central high grasslands. Baja California and Baja California Sur in the north west differ from the rest of Northern Mexico as the peninsula is fertile, with an almost Mediterranean climate, and much of the food comes from the sea in the form of fish and shellfish. It was not until the 16th Century that migrants from other areas of Mexico began to arrive, bringing their appetites with them.