Hidden fortress

The Detroit Free Press has an article by Rob Quinn  about a discovery on (or, technically, under) Alcatraz:

A surprising find under what used to be America's most notorious prison: Texas A&M researchers using ground-penetrating radar have discovered the remains of an old military fortress long believed to have been completely destroyed, reported the BBC.
The San Francisco Bay island was once the home of Fort Alcatraz, built upon the discovery of gold in the area and transformed into a line of defense during the Civil War. The fort never fired a shot during the war, though it did house Confederate sympathizers jailed for denouncing the Federal government.

Rico says there's more, but they want money for the rest of the article, and the BBC site doesn't reveal their article...