Over a 7‐year period from April 1982 to April 1989, integrated samples of rain and snow were collected at 32 sites by oil‐sealed storage gage stations in (and adjoining) the southeast California desert; station elevations ranged from −65 m to 2280 m, and the collection network covered an area measuring about 400 km in each dimension. Deuterium (δD) analysis of 406 samples shows that the average δD of summer precipitation was −56 per mil (‰) whereas winter values averaged −78‰, averaged annual values were close to −69‰ because most of the area is in a winter‐dominated precipitation regime. We found no correlation between wetness or dryness of a season and the δD of its precipitation. The δ18O versus δD plots show that rain samples define a line of slope 6.5, less than the 8 of the Meteoric Water Line, whereas snow samples define a line of slope 9.2. These differences in slope are the result of isotopic fractionation which occurred during evaporation of raindrops but not during sublimation of snow. Trajectory plots of 68 of the major storm events show that all of the winter storms originated in the Pacific, and passed over high mountains before reaching our collection stations. However, 21 of the 30 summer storms had trajectories that originated either over the Gulf of Mexico or the subtropical Pacific and traveled either west or north to reach our stations, without traversing high mountains. The difference in δD between winter and summer precipitation is due to different air flow patterns during those seasons.

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We compare isotopic data on modern groundwater recharge, estimated from a 7‐year collection of precipitation samples, with the isotopic compositions of 82 samples from wells and perennial springs collected in southeastern California. Over half the samples represent recharge that is considerably more depleted in deuterium (δD) than the lightest (winter) precipitation δD values now precipitating in nearby areas. Wells in the vicinity of irrigation canals fed from the Colorado River contain water whose δD resembles that of the irrigation canals, and wells adjacent to the Mojave River are recharged by Mojave River water. The remainder of the samples from the 17 hydrologic units discussed in this paper include one or more whose δD values are depleted in deuterium by at least 10‰ compared to recharge estimated from modern winter precipitation. A plot of δ18O versus δD for 56 wells and 22 springs shows substantial scatter (R2=0.66) and defines a slope of 4.9, which is lower than the slope of the Meteoric Water Line. This slope and the scatter of the data suggest these diverse waters were evaporated to different degrees before recharge, and they may also have exchanged oxygen with solid mineral phases. We interpret the fact that many groundwaters in this region have lower δD values than modem precipitation to indicate that recharge of many of the groundwater basins occurred during an earlier period, probably the late Pleistocene, when winters were colder, evaporation rates were lower, and precipitation was quantitatively greater and isotopically lighter.

The water content of the breccia is 150 to 455 ppm, with a deltaD from-580 to -870 per mil. Hydrogen gas content is 40 to 53 ppm with a deltaD of -830 to -970 per mil. The CO(2) is 290 to 418 ppm with delta (13)C = + 2.3 to + 5.1 per mil and delta(18)O = 14.2 to 19.1 per mil. Non-CO(2) carbon is 22 to 100 ppm, delta(13)C = -6.4 to -23.2 per mil. Lunar dust is 810 ppm H(2)O (D = 80 ppm) and 188 ppm total carbon(delta(13)C = -17.6 per mil). The (18)O analyses of whole rocks range from 5.8 to 6.2 per mil. The temperature of crystallization of type B rocks is 1100 degrees to 1300 degrees C, based on the oxygen isotope fractionation between coexisting plagioclase and ilmenite.

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