I inherited farmland from my grandfather but it was a life estate for my mother first. Now that she has passed, when I sell this land do I pay capital gains on the value at my grandfather's death or my mother's death? My grandfather's death was before the unified transfer tax system.

I inherited farmland from my grandfather but it was a life estate for my mother first. Now that she has passed, when I sell this land do I pay capital gains on the value at my grandfather's death or my mother's death? My grandfather's death was before the unified transfer tax system.
In my opinion you have to pay on the value at your mother's death...