The Rock is another name for Alcatraz Prison, one of the most infamous prisons in history. Many a criminal resided there at one time or another, including Al Capone. Several movies were made about Alcatraz as well, including The Birdman of Alcatraz, Escape from Alcatraz, and one actually called, The Rock. This isn't Alcatraz, although a similar type facility is located closeby. team_CHETT had a now archived cache hidden close to here that explained a little of that prison's history, and can be seen at GCJA60.
This may not be Alcatraz, but there is a rock. This should be a quick park-& grab unless it's been raining A LOT. In that case, a little wading may be necessary. Please pull completely off the roadway as to not interfere with traffic. Also, please replace and cover the cache exactly as you found it for the next geocacher's experience.