There are 4 plaques with interesting information in this area.
At the listed coordinates you will find a boulder with a plaque. Take the last 3 numbers of the year this event started and subtract 559, this will give you the North coordinates .XXX. Subtract 589 from the last 3 numbers of the year for W.XXX. This will take you to another plaque (railroad bridge one).
On the railroad plaque find the date when the wooden trestle was built. Take the last 3 numbers and subtract 411 for N .XXX and 547 for W XXX. This will take you to the final cache.
You can validate your puzzle solution with
certitude.