Determine mineral values at inheritance

I inherited my minerals with my mom’s death in 2020. I am now considering an offer to sell them. but I would really like to know my position from a capital gain or loss.

I tried the CAGI website for my account, but they only go back to 2022. And those values looked really low for the revenue they were generating as compared to today.

So is there a way a mere mortal can ascertain the value I would use as a base for my minerals near Toyah in the Alpine High?