California Family Code Section 2552 generally requires that for purposes of dividing community property that assets and debts be valued “as near as practicable to the time of trial”. If you are settling a case this usually amounts to as close as possible to the date the case is settled.
There are a few exceptions to this rule, pursuant to which a court upon the filing of a proper motion would allow an alternative valuation date.
As an example, if there is a community business in which one spouse actively participates and can have a significant impact on the the value of the business most courts would value that business as of the date of separation. The logic is that if the “in spouse” put post separation efforts into the business, those efforts would result in separate and not community property. This also protects against the “in spouse” driving the business into the ground after separation to lower the value at which it is awarded to them.
It should also be noted that assets that generally will not fluctuate in value except for post separation deposits or withdrawals, such as a checking account, are in all actuality going to be valued as of the parties’ date of separation. This is because presumably post separation deposits would be separate property contributions and a party expending funds from an account post separation would be depleting community property and should be charged with it.
This is different than an investment account which might significantly fluctuate in value from the parties separation until the date of trial. As to those types of assets you are back to the general rule that they are valued as close as possible to trial or separation.