These arrows don't point to the Fortress of Solitude. In fact, they point east and west (well, some of them do). A cool story of a quickly-obsoleted solution.
More at http://goo.gl/b73MB2, http://goo.gl/vnfHZw, http://goo.gl/NhoHuo, http://goo.gl/vyTfba
(h/t Mary)
These Really Exist: Giant Concrete Arrows That Point Your Way Across America
Every so often, a hiker or a backpacker will run across something puzzling: a ginormous concrete arrow, as much as seventy feet in length, just sitting in the middle of scrub-covered America. What are these giant arrows? Jeopardy champ Ken Jennings solves the mystery.