The four locks in question are right in a row to enable the canal to gain some serious height in a very short distance. Purpose was to get the canal elevated quickly to cross a narrow neck of land: the approx half mile distance plus the four locks eliminated some 4 miles of canal building around a loop of the Potomac River.
Here are some shots of each of the four locks:
Lock 47, again looking upriver. This lock was collapsing inward so the National Park service filled it in to prevent that from happening. Lock 48 is visible beyond.
Lock 48, nicely preserved, looking upriver to Lock 49 beyond. The "pockets" on either side show up nicely here. This is where the open lock gates would be tucked so they would not interfere with the passage of the canal boats. The little bridge is a modern tourist convenience--it was not there during canal operations.
Lock 49, looking upriver, with an original mule barn in the distance. This lock is also in great state of preservation.
You can imagine why running here is such a treat. Not only are you largely in the woods on a gravel trail, you get to see all this great historic archeology.