The War Department marker for Anderson’s Brigade is on the north side of Mansfield Avenue. (Mansfield Avenue tour map) It shows the location where the brigade spent the night before opening the fight the next morning in the Battle of Antietam.

From the marker:

U.S.A.
First Army Corps
Anderson’s Brigade of Meade’s Division bivouacked in this low field on the night of September 16, 1862.

Its outposts were established in the south edge of the wood in front and beyond the Hagerstown Pike to the west.