The Trans-Mexican Volcanic Belt is best known for calc-alkaline volcanoes such as Pico de Orizaba and Popocatepetl stratovolcanoes as well as calderas and pyroclastic cones; however it also features scattered alkali basalt volcanism. It lies at an angle to the Middle America Trench unlike the more typical volcanic arcs of Central America; some theories consider the belt to be independent from the trench. In its eastern region lies the Cofre de Perote and a group of volcanoes including the Naolinco Volcanic Field.