along US Hwy 34.
Just inside this side of the grove of trees on the right, there is a pipeline where the railroad used to be. The treaty line intersects with the county road a little further away, but not as far as the top of the hill in the distance. (Unfortunately I did not go that far to take a look at the exact spot.) The county highway is the boundary between Bureau and LaSalle counties.
Near the southeast corner of Mendota is the intersection of East 4th and North 42nd roads. North 42nd goes off to the right (east). It is almost an east-west road, and follows the Indian Boundary line, as it's called on old plat maps of the county.