The upper and middle Verde River watersheds in central Arizona are primarily in Yavapai County, which in 1999 was determined to be the fastest growing rural county in the United States; by 2050 the population is projected to more than double its current size (132,000 in 2000). This study combines climatic, surface-water, ground-water, water-chemistry, and geologic data to describe the hydrogeologic systems within the upper and middle Verde River watersheds and to provide a conceptual understanding of the ground-water flow system. The study area includes the Big Chino and Little Chino subbasins in the upper Verde River watershed and the Verde Valley subbasin in the middle Verde River watershed.
The Big Chino subbasin, in the upper Verde River watershed is 1,850 square miles in area. Within the subbasin, Big Chino Valley and Williamson Valley encompass about 570 square miles excluding the surrounding mountains and the western part of the Coconino Plateau. The valleys are filled with alluvial deposits eroded from adjacent uplands and interbedded basalt flows. Median thickness of the combined alluvial deposits and basalt flows is about 435 feet. The estimated volume of saturated basin-fill deposits within the valleys is about 155 million acre-feet. Beneath the basin-fill aquifer is a sequence of water-bearing Paleozoic formations that receive recharge where they crop out along the western boundary of the subbasin.
