43 C.F.R. § 10005.13
In accordance with the Act, the Commission has the authority to implement projects throughout the State of Utah. The Commission believes that, to be effective, the plan must be prepared, and evaluated, from a state-wide perspective and that, within the state, an ecosystem-based approach is appropriate. There is no one correct way to define an ecosystem or to approach ecosystem planning. The Commission concludes that, for its planning purposes, the watershed provides the appropriate geographic and ecological reference within which to evaluate proposed projects and otherwise plan its activities. In delineating watersheds, the Commission will be consistent with the best ecological and hydrological science and, to the extent possible, with the ecological and hydrological units currently used by the State of Utah, the U.S. Fish and Wildlife Service, and other applicable Federal agencies. The Commission recognizes that mitigation and conservation projects may vary in scale and that, therefore, one standard set of watersheds is not necessarily appropriate for all projects. For example, a more localized project may best be analyzed from a "watershed within a watershed" perspective. Alternatively, a large-scaled project may need to be visualized from the perspective of a major river basin consisting of several watersheds. The Commission will prepare, and have available for public use, a list or map that identifies major basins, watersheds, and, where appropriate, hydrologic units within watersheds, that the Commission will use to organize its mitigation and conservation activities. This list or map may be revised from time to time as circumstances change.
43 C.F.R. § 10005.13