DRECP Subareas were based on logical groupings of USDA Ecoregion Subsections, which created 10 subareas in the DRECP Plan Area. Grouping of the subsections to create the subareas was based on spatial configuration, ecological relationships, and broader USDA Ecoregion Section designations. Grouping of the subsections also reduced the slivers and small portions of subsections that occur around the boundary of the Plan Reas.

This layer contains polygon features of Ecological Units for the state of California as described by ECOMAP (1993),.. "Ecological types are classified and ecological units are mapped based on associations of those biotic and environmental factors that directly affect or indirectly express energy, moisture, and nutrient gradients which regulate the structure and function of ecosystems. These factors include climate, physiography, water, soils, air, hydrology, and potential natural communities."