predominant climates in the region are tropical savanna (primarily in the south) and tropical monsoon (primarily in the north). There are also small central areas with a temperate climate due to elevation. The annual rainfall on the Atlantic or northern slope is 3,960 mm (156 in) and the maximum temperature about 35 °C (95 °F) in the shade. The Pacific slope has a light rainfall and dryer climate. The narrowness of the isthmus, and the gap in the Sierra Madre, allow the trade winds from the Gulf of Mexico to blow through to the Pacific. Normally, these winds are not particularly strong, but periodically, a surge of denser air originating from the North American continent will send strong winds through the Chivela Pass and out over the Gulf of Tehuantepec on the Pacific coast. This wind is known as the Tehuano. The region has one of the best wind resources in Mexico, with several wind farms. People and culture In the Oaxaca half of Tehuantepec, the population is composed mostly of indigenous Zapotec peoples. The women are the traders in the Oaxacan Tehuantepec area and do little menial work. Known as "Tehuanas", these women are known throughout Mexico for their colorful dresses, assertive personalities, and relatively equal relations with men, leading some to characterize them as "matriarchal." Cuisine The cuisine of the region is based upon traditional foods and ingredients. Dishes may range from simple to elaborate; most dishes incorporate maize and moles. Common items include tamales made with iguana, chicken, beef or armadillo; guetabingui (fried balls of rice and shrimp); garnachas topped with dried queso Oaxaca; and pozol, a maize-based drink. Tehuantepec route Since the days of Hernán Cortés, the Tehuantepec isthmus has been considered a favorable route, first for an interoceanic canal, and since the 19th century for an interoceanic railway. Its proximity to the axis of international trade gives it some advantage over the Panama route. The Isthmus of Panama, however, is significantly narrower, making for a shorter traversal, even if the canal is farther from trade routes. The 1854 Gadsden Purchase treaty included a provision allowing the U.S. to transport mail and trade goods across the Isthmus of Tehuantepec via a plank road and railroad. The 1859 McLane–Ocampo Treaty, which Benito Juárez signed but was never ratified by the United States Congress, would have given the U.S. extensive transit rights along the same route. When the