Which of the following cities is NOT part of the Solar Plan?

The Solar Plan is an initiative aimed at increasing the use of solar energy within specific regions, often focusing on cities that have made commitments to sustainability and renewable energy sources. In this context, the cities involved are typically those with ongoing solar projects or legislative support to develop solar infrastructure.

San Bernardino, Riverside, and Los Angeles are actively participating in such solar initiatives, demonstrating efforts to enhance renewable energy production and sustainability within their jurisdictions. On the other hand, San Diego, while known for its own active solar initiatives, has historically not been a part of the same Solar Plan framework as the other listed cities in many contexts.

Thus, in this multiple-choice question, San Diego can be identified as the city that is not included in the specific Solar Plan referenced, making it the correct answer. This distinction is vital for understanding regional energy policies and the specific initiatives each city undertakes in striving for greater renewable energy utilization.