The Solar Programmatic Environmental Impact Statement (PEIS), released in July by the U.S. Departments of Energy and the Interior, would allow solar development on 919,705 acres of public lands in California: a bit more than 1437 square miles. That's a larger area than that covered by the cities of Los Angeles, San Diego, San Jose, Bakersfield, Fresno, and Sacramento combined.
Environmental Impact Statements for any program or project generally describe a range of alternatives to the proposed action, often including a "no action" alternative, and compare the projected environmental effects of each alternative. The agency preparing the EIS usually designates a preferred alternative. Under the PEIS's preferred alternative, referred to in the document as the Solar Energy Development Program Alternative, 153,627 acres are included in the state's two Solar Energy Zones (SEZs), while the remaining 766,078 acres are considered so-called "variance zones," on which solar power generating stations may be built provided they pass standard environmental review, and a few extra hurdles imposed by the Bureau of Land Management.
As shown in this map of California SEZs and variance lands, the bulk of California variance lands are to be found within about 40 miles of the Colorado River. Significant additional variance tracts would be defined in the Interstate 40 corridor and the California desert portion of the Interstate 15 corridor, including much of the formerly proposed Pisgah SEZ and a broad swath of the Cadiz area. Abundant areas of checkerboarded variance areas would also be established in the Barstow-Dagget area, the California City area, and a corridor running eastward from the vicinity of Victorville to east of Twentynine Palms.
According to the PEIS, the Department of the Interior intends to guide most solar developers to the SEZs. The PEIS itself constitutes a significant incentive to developers to focus on the SEZs: if they propose a project inside a SEZ, some of their environmental review paperwork has already been done. But as the PEIS says
The variance process provides an opportunity for developers to propose applications outside of identified SEZs and complements the directed development approach in the program alternative. Variances may be needed in the near term because the lands identified as SEZs might be insufficient to accommodate demand for utility-scale solar development or may not have access to adequate transmission capacity to facilitate such development. In addition, there might be market, technological, or site-specific factors that make a project appropriate in a non-SEZ area. The variance process, however, is intended to be the exception rather than the rule.
Of the total proposed California variance lands, 730,616 acres -- 95% of the total -- is within the BLM's California Desert Conservation Area, much of which is covered by the developing Desert Renewable Energy Conservation Plan (DRECP), a state-level program intended to mediate the opposing imperatives to develop the desert for renewable energy and to protect that same desert's ecological resources. That process is still in its scoping phase, and any development on variance zones within the DRECP plan boundaries would have to pass muster under that plan as well.
You can explore the boundaries of California's SEZs and variance areas by using the National Renewable Energy Laboratory's Solar Energy Environmental Mapper.