Yours truly made the chart above from data contained in a report by the National Center for Educational Statistics. (I was pointed to the report by Inside Higher Ed.) The chart comes from Table 15 of the report. For California, it suggests that the pool of [public school] high school grads in California will shrink in the coming years. I found some anomalies in the data projections elsewhere in the report for California and am not an expert in this area. Of course, for UC, the pool of potential undergrad admits is not limited to California or to public schools.
Nonetheless, if there are any experts in this area that can interpret the data, they are encouraged to comment.
The table is at
The full report is at