" I’m trying to figure out how it got the name to begin with...."
A "niggerhead" is a big rock you hit when digging a ditch.
Just a guess.
There is a type of prolific daisy wildflower native to that part of Texas. It has had several colloquial names over the years, including “Balck-Eyed Susan, Yellow or Ox-Eye Daisy, Nigger-Head, Golden Jerusalem, and Purple Cone-flower.” See the following link:
http://www.nature-and-flower-pictures.com/black-eyed-susan.html From my experience as a native Texan, the name “Nigger-Head” was the most common.
It seems reasonable to me that the hunting lease was named after the flowers found on it, which is a common way to refer to fields or other areas within a large parcel of land.