Community property is everything that isn’t separate property. There is a presumption that all property in a marriage is community unless the separate property can be traced by clear and convincing evidence.
Depending on the type of property, you may not be able to prove your separate property claim. Besides bank statements and brokerage statements, you may also use other documents proving your claim, like a prior divorce decree, an estate tax return, real estate deed records, prenuptial agreements with a schedule of separate property, gift tax returns, and other types of documents.
Mixed property – both community and separate – arises when separate property and community property are mixed. The easiest example of this is a 401k. If you had been contributing to a 401k prior to marriage, that is separate property. As community dividends and interest are reinvested after the marriage, the 401k becomes a mix of separate and community property. Also, as continued deferrals from community property earnings are invested, the account becomes even more mixed.