This is a quick field puzzle. As you approach the bridge from either end, you will see a sign. Your job is to find out what that sign says, and use the answer to help find the cache.
If the signs says:
1. Trail Narrows - then look under the NW corner of the bridge
2. Watch for Pedestrians - then look under the SW corner of the bridge
3. Bridge Ices In Winter - then look under the NE corner of the bridge
4. Trail May Flood - then look under the SE corner of the bridge