I know when my daughter started college 5 years ago, the dean was up front that there was a demographic cliff coming up, I wonder how much of the decline is that.
what's a "demographic cliff"?
Presumably, the school was built / staffed for a certain regular enrollment that reflected some percentage of the people in state.
For California specifically:
https://data.census.gov/profile/California?g=040XX00US06
You can see the peak of 25-30 somethings, and then it drops off.
When you start looking out at the 15-19s there are 400,000 fewer than the 25-29s (roughly 3M -> 2.6M). That then means that enrollment is going to drop and things will need to be cut.
The school that I went to for grade school was built for baby boomers. It was large, and the next town over likewise had a large school. When I went it was a bit empty, not too bad though. It picked up again with the echo.
The towns have recently closed half of each school and combined classes because there isn't enough students to keep two sets of classes running at reasonable funding levels (having a class of five 3rd graders and six 4th graders is great for student to teacher ratios ... not so much the budget of a small rural school).