Here are my maps. The higher the percentage of land cultivated, the darker yellow the counties appear.
The increasing amount of land developed into farmland is definitely visually apparent. Generally, farmland spread to the west, but the areas with the very highest proportion of developed land stay more or less the same. Dark yellow is mostly concentrated in eastern Kansas in all three maps. Although westward expansion and the construction of irrigation infrastructure allowed crops to be grown farther west, the best farmland remained in the northeast.
Got it.