We are referring to the system, not just the generation assets (which are accessible over many states).
Any connection of Sierra to any central valley specific DER resources excludes the Sierra from the DER system. If you use that summary definition from the brief FERC order, anyone producing solar in the Western Interconnection (1/3 western half of U.S. and Canada) meets such criteria. However I previously understood your argument to be that fully isolated micro-grids could be built from DER systems in the foothills and mountains of the Sierra, but the criteria of a DER system enshrines that it can only exist locally.
DER systems may be either connected to the local electric power grid or isolated from the grid in stand-alone applications...DER systems can provide voltage support and enhance local reliability.
https://www.nrel.gov/docs/fy02osti/31570.pdf
Sierra assets are simply not connected locally to Central Valley resource assets. In a very general sense, distributed renewable generation at any corner of the Western Interconnection could influence use at a distance a couple thousand miles away. But that is a part of the argument for building more long distance interconnects, not severing them.