In the southwestern United States, where water extraction is beginning to exceed the limited groundwater recharge, assessing regional aquifers is becoming increasingly important. Ideally, one would like to assess these aquifers over time to determine anthropogenic changes. In general, potable groundwater in the southwestern United States is more conductive than in the eastern or northwestern part of the country due to greater ion content. The latest generation of powerful airborne electromagnetic (AEM) systems can directly image groundwater if it contains some dissolved solids and if it is under conditions of little or no human cultural interference.

The San Pedro River...

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