First observation of DST was in 1931, but only for the state of Baja California. It used the "Hora del Centro" from April 1 to September 30, and the "Hora del Oeste" the rest of the year. Until 1996, Baja California was the only Mexican state to officially observe DST every year, coinciding with the observance of DST across the border in San Diego, California. In addition to that, the states of Durango, Coahuila, Nuevo León and Tamaulipas unofficially observed DST in 1988 as an experiment, starting on the first Sunday in April and ending on the last Sunday in October. These states abandoned DST the following year and did not return to it until DST was adopted nationwide.