If a property is purchased while married but only one is on deed, is it still community property in a divorce in CA?

Assuming the house was bought during marriage with community funds, and the Married Woman's special presumption does not apply ( it only applies to a very limited set of circumstances), the fact that only one name is on the deed does not preclude the presumption that the house would be community property.

Property purchased during the marriage is presumed community property. The person who is on title and who is claiming the property is separate property must rebut the presumption. If h/she purchased the property using separate property assets then it may be separate. However, if any community assets were used then it will not be found to be separate (no use of income from wages can be used to pay the mortgage or make improvements).

Probably it depends on whether the buyer used separate money to buy it or community money.