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Why is this study important?
The report applies multiple lines of evidence to examine contributions to the baseflow of the upper Verde River. It concludes that the Little Chino aquifer provides approximately 14 percent and the Big Chino aquifer system provides between 80 and 86 percent of the Verde River baseflow measured at the Paulden stream gauge.
Wirt, Laurie, DeWitt, Ed, and Langenheim, V.E., editors, 2005, Geologic framework of aquifer units and ground-water flow paths, Verde River headwaters, north-central Arizona: U.S. Geological Survey, Open-File Report 2004-1411. Multiple lines of evidence indicate that the major source of groundwater to the upper Verde River is the Big Chino aquifer at its groundwater outlet near Paulden (80 to 86 percent) with the Little Chino aquifer providing about 14 percent of 17,000 acre-ft/yr. Flowpaths from the Big Chino basin-fill aquifer and its underlying carbonate aquifer converge north and east of Paulden. The Big Chino basin-fill aquifer and D-C zone of the carbonate aquifer are strongly connected between Paulden and upper Verde River springs. Here, the D-C zone of the carbonate aquifer acts as a conduit for outflow from Big Chino Valley and provides as much as 15 percent of ground water attributed to the Big Chino basin-fill aquifer. Distinctive water-chemistry changes along the Big Chino outlet flowpath are largely caused by dissolution of silicate minerals, leaching of trace elements, and mixing with ground water from the D-C zone of the carbonate aquifer. Inverse modeling constrains the potential contribution from the M-D sequence of the regional carbonate aquifer north of the upper Verde River to less than 6 percent of base flow at the Paulden gauge. Numerous stratigraphic and structural features influence ground-water flowpaths and the location of springs supplying base flow to the upper Verde River. Prominent features that provide preferential flow in the regional carbonate aquifer include karst openings, faults and fractures (including the horsetail splays at the terminus of the Big Chino Fault), joint sets parallel to monoclines (such as the Limestone Canyon Monocline), and a basalt-fill paleochannel that straddles the basin-fill aquifer boundary near Paulden. Basalt flows have high-overall permeability and sometimes provide important flowpaths, owing to extensive columnar fractures and rubble zones. Igneous and metamorphic basement rocks usually have very low permeability and define the bottom and edges of the basin-fill aquifers. Groundwater movement within the basin-fill aquifers is from the valley margins and tributaries toward the valley center and then down the longitudinal axis of the valley toward the basin outlet. Elongate basin-fill deposits tend to narrow and thin toward their topographic outlets, resulting in low-altitude springs that correspond spatially with the distal end of the aquifer. Major buried obstacles to ground-water movement include resistive volcanic plugs and shallow basement rocks in northern Little Chino Valley and a playa deposit in central Big Chino Valley. In lower Big Chino Valley, a basalt-filled paleochannel straddles the basin boundary between the basin-fill aquifer and the carbonate aquifer, offering an intermediate conduit between alluvium and carbonate aquifer units. Synthesis of independent data from a variety of geological, geophysical, hydrological, and geochemical sources provides a more detailed conceptual understanding of the geologic framework, the aquifer units, and major ground-water flowpaths in the Verde River headwaters. CLICK HERE TO READ THE FULL REPORT
