Several articles state he was an agent. Agent wrote the land lease contracts for the mineral rights. Their pay was often delayed compensation from future well production. One freeper said one tenth of one percent. See if you can find the 1950 census!
If he had formed a trust the income may have gone into the trust. Living frugally was a pattern an entire community nearby exhibited. But those who knew the truth knew they had holdings worth millions kept for future rainy days or their ancestors. (early shares of Xerox IIRC) How would similar assets show up in census?
FREEPERS: Doing the work the mainstream media refuses to do.
The 1940 census is last one that was just released. 1950 census not available for another 10 years.