Step up in basis for property owned in another state following death

My friends live in CA (a community property state) and own a rental property in CO (a non-community property state).  One of them recently passed away and the survivor is going to sell the CO rental property.  We understand that half of the property will receive a stepped-up basis upon the date of death for CO income tax purposes (when reporting the eventual sale on their tax return).  What we are unsure of is the basis that will be used on their Federal return.  Since they are CA residents, are they able to follow the community property tax laws from the state of residence on their Federal tax return (i.e. receive a full  step-up in basis), or must they follow the laws of the state of CO for the basis to be reported on their Federal tax return?