Blackjack Country

We noted today that Elmore, Arkansas, is -- according to O. Henry -- located in "blackjack country." From the context of "A Retrieved Reformation" we understand that the phrase connotes a backwoods, out-of-the-way place. With a little research I found that 18th century farmers

recognized the poorer soils in the blackjack country of the eastern uplands, so called because of the predominance of blackjack oak, a small, scrubby, thick-barked tree especially suited to poor soils.

The upshot: observant farmers would not settle in blackjack country because the soil was poor; thus "blackjack country" is typically a sparsely populated region -- or, at least it was in the early 1900's.