Caramel, the area was a river, they believe had a great flood and drown many dinosaurs. The larger ones piled together, and eventually as the river slowed, silt and sludge covered them over many eons. This was why mostly large dinosaur bones were found .
This occurred over millions of years. Then, the layers were pushed up vertically by tectonic plate movement, and then erosion uncovered part of the bones. I’m guessing the explorer was looking for gold ore veins, but saw the bones sticking out and started a different discovery path.