Calculating cost bases of dock lost in declared disaster

[JJBSR57]

I'm trying to complete my 2020 return. I lost my dock in Hurricane Sally which was declared a Federal disaster. The dock was part of the home when I first purchased the house. So how do I calculate the cost bases of the dock? 

Thanks!

[JillS56]

Do you have any idea what the cost to purchase a dock at that time would be?   How long ago did you purchase the house?   The cost basis of the dock would have been the value of the dock at the time you purchased the house.