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The Aridity conditions in the northwest Mexican region formed by the states located around the Gulf of California are studied The Annual Arid Cover Index (AACI) is defined as the fraction of the studied area with Martonne aridity index values less or equal to 5. The AACI is used to describe variations in the extension and localization of the extremely arid zones during the 1950-1990 period The results show a tendency of the extension of the arid zone to reduce: 30 % in 41 years. A statistically significant explained variance of 32 % between the AACI and the sea surface temperature (SST) of the California Current zone was obtained Correlation between the Southern Oscillation and the Pacific North America indexes show a smaller variance: 17 and 3 %, respectively. The multiple regression model gives a total coefficient of determination of 42 %. The variations in the geographical localization of the extremely arid zones show that the Altar Desert and the meridional zone of the Baja California Peninsula have the more persistent arid conditions in the studied region.