...Wright Brothers Park. That is the Quadrant III map, which they should figure out by knowing what Quadrants I, II, III, and IV are, mathematically. Then, they get to graph the two equations of the line, they should get something similar to:
This puts them in front of the wall where we like to picnic and watch the planes take off and land. Great fun for us. They went right to our usual location, and it took no time at all to find the clue. Retrieving it was a bit tricky, since I threw the clue over the cliff. It had some fishing line tied to it, so they reeled it in after only a little difficulty. If they look around there, they will find the next clue.