By John A. Izbicki and Robert L. Michel
U.S. GEOLOGICAL SURVEY
Water–Resources Investigations Report 03-4314
Sacramento, California 2004
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Tritium and carbon-14 data in water from wells in the Mojave River and the Morongo ground-water basins in the western part of the Mojave Desert show recent recharge focused in the floodplain aquifer along the Mojave River. Older ground water was present in parts of the regional aquifer that surround and underlie the floodplain aquifer. Movement of water between the floodplain and the regional aquifers occurs near on the upgradient side of faults as water from the regional aquifer discharges to the floodplain aquifer and on the downgradient side of the faults where water from the floodplain aquifer recharges the regional aquifer. On the basis of carbon-14 ages, corrected for mineralogic reactions with aquifer materials, water from some wells was recharged more than 20,000 years ago. Geochemical data show ground-water recharge has gradually decreased as the climate changed since that time.
Purpose and Scope
Background and Previous Studies
Carbon-14 and Carbon-13
Sample Collection and Analyses
Mojave River Ground-Water Basin
Morongo Ground-Water Basin
Carbon-14 and Carbon-13
Areal Distribution of Carbon-14 Activities
Carbon-14 Activities Along Selected Geologic Sections in the Mojave River Basin
Sections A-A', B-B', and C-C'
Section D-D' and E-E'
Interpretation of Ground-Water Age Along Selected Flow Paths
Initial Carbon-14 Activity
Interpretation of Carbon-14 Ages Along Selected Flow Paths
Flow Path 1: Surprise Spring Basin
Flow Path 2: Upper Part of the Mojave River Basin to the East of the Mojave River
Flow Path 3: Upper Part of the Mojave River Basin to the West of the Mojave River
Limitations on Carbon-14 Interpretations
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