This means you would use the masculine definite article "el" before it:
* El estado de California (The state of California)
However, you may occasionally see "estado" used with the feminine article "la" in some specific contexts, particularly when referring to a specific state's condition or situation. For example:
* La estado de la economía es preocupante. (The state of the economy is concerning.)
In this case, "estado" is more similar to the English word "state" meaning "condition".
It's important to remember that in most cases, "estado" is masculine, and using "el" before it is the standard practice.