Cost basis on sale of mineral interest

**i need to find out what my minerals right were worth in 1974 since I sold half of them in 2018 and my CPA needs to know fir tax purposes. Is there a public record site where I can research the value of minerals in Midland county Texas?

Your original cost basis is the price you paid when your purchased. Or it could be the estate value if you inherited. If you received the minerals as a gift, then your basis would that of the donor. Regardless, you must reduce your original basis by the depletion that you have taken over the years. If your cumulative depletion exceeds the original basis, then your basis at the time of sale would be zero.

Thank you for your response. I inherited the mineral rights and the estate had no value on gnoses interests when I inherited them. That’s why I am trying to find out how to determine what their value was in 1974.