Low-angle infrared aerial photography, in conjunction with conventional aerial photographs and ground truth, has proved effective for locating active faults in the Imperial Valley. Slight differences in soil moisture, which may depend upon faulting, affect the vigor of plants within a field, and plant vigor can be recorded on infrared Ektachrome film. The effectiveness of the method depends on the presence of vegetation, and upon crop type and plant maturity. A rectilinear pattern of fields aids in detecting faults which do not parallel section lines. The method should be useful in other vegetation-covered areas, including alluvial plains and prairie areas blanketed with glacial till.
Oblique infrared photo coverage was obtained at altitudes of 2,000 to 5,000 ft for much of the east and west sides of the Imperial Valley. Two previously unmapped zones of active faulting were located along the eastern side of the valley, and also a probable fault along the southwest side of the Superstition Hills.