A view of the Verde River, north of Clarkdale, Arizona. Red, well bedded rocks in background are nearly horizontal beds of the Supai Formation.
Analysis of aeromagnetic and gravity data provides new insights into the geometry of geologic structures of the upper and middle Verde River watershed, Yavapai County, Arizona. Magnetic anomalies reveal hidden volcanic rocks lying at shallow depths beneath the ground surface in Williamson, Little Chino, Big Chino and Verde Valleys in the upper Verde River watershed, Yavapai County, Arizona. Concentrations of shallowly buried volcanic plugs or centers are located down-gradient of springs (Del Rio) and perennial flow (Williamson Valley), suggesting that these volcanic centers or plugs may retard ground-water flow. Magnetic data also map paleo-channels filled with 4-6 Ma basalt as Big Chino Valley formed and subsided during late Tertiary time. The magnetic data reveal a predominantly northeast- to north-striking structural grain within Proterozoic basement rocks, in contrast to the generally northwest strike of late Tertiary faults in this region. The magnetic grain may serve as a proxy for fracturing and faulting, an important source of permeability in these generally impermeable rocks. Magnetic and gravity data also delineate exposed and concealed faults within the study area. The Big Chino fault and Verde fault zone have the largest amounts of vertical throw of any fault in the study area based on gravity, magnetic, and limited well data. These faults bound deep (1-2 km) basins in Big Chino and Verde Valleys. The geophysical data also reveal concealed faults in Williamson Valley that bound a previously undiscovered basin with approximately 1 km of Cenozoic fill inferred from inversion of gravity data. Little Chino and Lonesome Valleys, including the upper reach of the Agua Fria basin, are characterized by basin fill which nowhere exceeds 1 km and has a more irregular distribution with local, north- to northwest-striking pockets of thicker sediment. A 15- to 20-km-long northwest-striking magnetic lineament that passes through Page Springs in Verde Valley can be used to project a fault 5-10 km northwest and southeast of its mapped trace. The colocation of the lineament, mapped fault, and the spring suggests structural influence on the location of this large spring.
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For questions about the content of this report, contact Vicki Langenheim.
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