Continuing south on the main highway, there’s little between El Rosario and the 28th parallel, where an enormous metal monument marks the border between the states of Baja California and Baja California Sur; you’ll have to set your watch forward an hour when you cross. GUERRERO NEGRO, just across the border, offers little in the way of respite from the heat and aridity that has gone before (winters, however, can find the town quite chilly). Flat and dust-blown, it was only established in the 1950s as a supply centre for Exportadora de Sal, the world’s largest salt manufacturer, and is surrounded by vast saltpans and drab storage warehouses. At most times of year you’ll want to do little more than grab a drink and carry straight on, especially if you don’t have a car – it’s a dispiriting place to navigate on foot. In January and February (and, peripherally, Dec & March–April), however, Guerrero Negro is home to one of Mexico’s most extraordinary natural phenomena, the congregation of scores of grey whales just off the coast.