The meteorologic characteristics and isotopic composition of precipitation events in the Southern High Plains, Texas and New Mexico, were monitored during 1 full year to estimate the natural recharge potential of the region's major aquifer. Precipitation events during spring and summer derive their moisture from the Gulf of Mexico. Temperature effects account for the isotopically enriched rainwater during this period, offsetting possible amount effects. During fall and winter, precipitation events acquire moisture from the eastern Pacific Ocean. Temperature as well as continental and altitude effects produce isotopically depleted precipitation during this period. Precipitation during events throughout the year that lasted for several days became depleted in both chloride concentration and isotopic composition, thus displaying a front effect. ¿ American Geophysical Union 1990