I'm not particularly familiar with 401(a) plans in general and CalPERS in particular. The following investopedia webpage on 401(a) plans in general suggests that it's the employer's choice whether contributions are pre-tax or after tax, but I don't know if that would be applicable to CalPERS. If made pre-tax they would be excluded from box 1 of the W-2. If made after tax they would be included in box 1 of the W-2 and would need to be tracked by the plan as after-tax-basis that would not be taxable when later distributed.
https://www.investopedia.com/terms/1/401a-plan.asp
