The Toluca Valley is a broad highland valley located immediately west of the Valley of Mexico. It is one of the highest valleys in Mexico with an average elevation of 2,570 meters above sea level ("masl"). The valley is part of the Trans-Mexican Volcanic Belt, with its soils of volcanic origin mostly dating from the Upper Cenozoic. Mountains sides have tertiary volcanic rock, mostly basalt and andesite along with pyroclastic matter and breaches. The valley floor is composed of lacustrine and sedimentary materials . The valley covers an area of about 700 square kilometres, running north south with a length of 35 km. Its width is about 20 km. Its northern border is marked by the Guadalupana Volcano, the Cerro el Aguila and the Sierra Monte Alto. Its southern extension is marked by the Tenango and Zempoala Volcanoes. Its eastern boundary is marked by the Sierra de Las Cruces and La Iglesia mountains and the west is defined by the Nevado de Toluca and the Sierra Morelos. These mountains, along with the elevation of the valley in general cause the area to experience cooler temperatures than the rest of the region.