Depreciation and land / structure cost basis breakdown

Last year I converted a primary residence to a rental, and am trying to estimate the breakdown of land / structure % for the cost basis.

 

The appraisal from back when I bought the property does not have a breakdown. My property taxes split the cost at 50% - 50%, which sounds high for the land and low for the structure (this is in San Francisco).

 

Questions:

- If I use this 50-50% split (leading to potentially-low depreciation), then in the future sell the property, is there any risk the IRS could argue that I should have used a higher cost basis, and that they recapture more than I depreciated?

- Is there another accepted way to estimate the %, other than the property taxes?