The location of the coast survey map makers 1854-1855 astronomical observatory on the east point of Hurricane Island was listed as LATITUDE 30 degrees 4 minutes 23 seconds and LONGITUDE 85 degrees 38 minutes 36 seconds. According to John A. Burgess in 1985,"On current navigational maps a piling is listed very near these coordinates in the open channel approximately one mile east south-east of the present day land's end (eastern tip of today's Shell Island). This corresponds with the probable location of a wharf and barracks built by Union forces on the north side of the island during the Civil War. These forces were an effective blockading effort by the Union Army to keep the channel closed to Confederate use. They even built a small prison camp and a cemetery here. Also, the site served as a place of refuge for Union sympathizers who came to the coast seeking help from the Union blockading force."   https://www.floridamemory.com/items/show/323050