Hi Tom,
First, sorry for your loss. You might want to contact an attorney in your state to determine how this might impact you and to explore the question further. Here are my thoughts: If the property still belonged to your son, then it may need to be reported on an estate tax return. If title transferred to you, then it would be your asset to report on your tax return. If the son's property reverted to you, you would determine the sale based on the stepped up basis as of the date of his death and what it sold for. Make sure to account for the expense of sale.
Thanks,
Dirk