What is the tax basis in a residential rental property obtained through foreclosure?

Over the past 23 years I loaned my mother amounts totaling $125,000 in principal in a series of loans each secured by a promissory note and related deed of trust which were properly executed and recorded. Last year the value of the notes exceeded the value of the home and she deeded the property to me via "Deed in lieu of foreclosure" (State of Washington). The value of the outstanding notes cancelled in the process exceeded the value of the house by $100,000 largely due to accrued interest. I have rented the property to a third party but am uncertain about how to calculate my basis.