Hydrologic Unit codes can range from two to eight digits, depending on the size of watershed being referenced. The HUC 1506 refers to the Salt River Basin, of which the Upper Verde watershed is a component. The Salt River Basin, HUC 1506, is 13,700 square miles in size. In contrast, HUC 150602, the Verde River Basin, covers 6,590 square miles within the Salt River Basin. Getting even more specific, the Upper Verde watershed, HUC 15060202, is 2,480 square miles in size, nested within the Verde River Basin.
A clickable map of water resources regions. The hydrologic unit codes, names, and sizes for the progressively smaller watersheds within these regions can be accessed by clicking on this map.
Watersheds provide the physical template for water movement through an ecosystem. The cycling of water through the system is summarized in the hydrologic cycle, to be covered in the next page.