and U.S. Army
Earth Science Applications, National Training Center, Fort Irwin

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Applying geology to understanding water resources

Faults provide information on potential conduits and barriers to groundwater flow

Earthquakes grind up rock in the fault zones, and this ground rock decomposes to clays in many cases; it is known as fault gouge. The broken rock in some cases acts as a good conduit for the flow of water, and in other cases the gouge acts as a dam to water flow. For these reasons, it is common to stripes of unusually green vegetation and even springs along faults. Fault locations therefore are targets for unusual habitats in the desert.

Topography provides clues to regional groundwater gradients

Elevations are highest overall in the northeastern part of the NTC at the Avawatz Mountains, and elevations generally decline to the south and west. This regional topography implies that present regional runoff and subsurface recharge of water is derived from that northeastern area. Local smaller mountains provide some rounoff and recharge, as well. Relatively little precipitation occurs now and in historic time (the last several decades), and records from surface materials (such as alluvium) deposited over the last 10,000 years indicates that the area was dry for the entire time. This dearth of precipitation and runoff means that recharge to the water stored in subsurface sediment is minimal. Subsurface water now being pumped from sediment basins probably dates from glacial ages, when the area was much wetter and cooler.

Gravity and aeromagnetic mapping lead to evaluation of basin size and thickness of water-bearing sediment

Shaded relief maps

Topographic maps

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