Alcatraz Island’s bedrock is called greywacke, a sandstone melange that was laid during the Cretaceous Period and is part of a geologic terrane that includes most of the City of San Francisco including Nob, Russian, and Telegraph Hills.

During the Pleistocene Epoch, the San Francisco Bay was free of water, and what is now the Sacramento River ran through the Golden Gate to the sea. The course of this river can still be traced on the floor of the bay as it winds around Alcatraz and nearby Angel Island. The Bay’s network of currents makes swimming it very dangerous, something that would later be exploited during the island’s use as a prison.

According to native histories, Alcatraz was a place of exile in ancient times and served as a site of refuge when the first Spanish came to the area.

One such Spaniard is the source of the island’s now iconic name. Naval officer Juan Manuel de Ayala y Aranza passed through the Golden Gate in August of 1775, charting the features and making contact with local Native American tribes. He gave names to many features, including what is now called Yerba Buena Island, a sandstone island he named La Isla de los Alcatraces, or "The Island of the Pelicans." This name was later adopted for Alcatraz when the United States took possession in 1846.

In the wake of the California Gold Rush, and with fears mounting that foreign interests might try to take control of the suddenly valuable region, President Millard Fillmore signed an order in 1850 placing Alcatraz Island, as well as several others in the Bay, under the control of the U.S. Army and directing the construction of defensive fortifications.

While the gun batteries of Alcatraz fortress were never called upon to defend the city, the remote nature of Alcatraz made it an ideal location for holding military prisoners. Confederate soldiers and sympathizers were housed here during and after the Civil War, as were so-called "rebellious" Native Americans.

Over the course of 29 years, only 36 inmates attempted to escape Alcatraz. Officially, there were no successful escapes, however, in the early hours of June 12, 1962, Frank Morris and brothers Charles and John Anglin slipped into the San Francisco Bay in a makeshift raft crafted from stolen raincoats. The trio worked for six months to widen the ventilation ducts inside their cells and then escaped through a utility corridor behind their cellblock.

Fragments of their personal belongings as well as the remains of their raft were discovered but the prisoners' bodies were never recovered.

After the Federal Penitentiary closed in 1963, Alcatraz was abandoned and declared surplus property by the U.S. Government. This led Native American rights activists to make several claims for the island based on the 1868 Treaty of Fort Laramie. A symbolic occupation of Alcatraz occurred in 1964.

In 1969, after a second occupation, a group of 89 American Indian activists set out for Alcatraz with the intention of laying claim to the island. After landing a small party, a proclamation was issued by The Indians of All Nations, claiming the island by right of discovery, and signing off with the famous cry, "We Hold the Rock!"

These activists' plans were nothing short of a sovereign zone for Native American independence, complete with an American Indian university, cultural center, and museum. For over a year, activists held the island with the population peaking at over 400 people, but restrictions on fresh water and electricity from the San Francisco government forced the occupation’s end.

Nevertheless, the movement was linked to many Native Rights protests during the 1970s and remains the inspiration for the annual Indigenous Peoples Sunrise Ceremony held each year on Alcatraz Island with the full support of the National Parks Service.

Today, Alcatraz Island is a national park visited by over 1 million people each year. The island is also home to a rapidly growing population of nesting colonial seabirds, including cormorants, snowy egrets, and black-crowned night herons.

The site is difficult to maintain—after decades of exposure to the salty, cold winds of the San Francisco Bay, airborne chlorides have penetrated the buildings’ concrete and degraded reinforcing steel. 

This specimen from Mini Museum is a piece of concrete salvaged by the National Park Service during restoration work on Alcatraz’s many buildings. As a part of the “Save the Rock” campaign, the NPS raised the funds needed to restore the island’s decaying infrastructure by selling pieces of the eroded concrete that needed to be replaced.

Both display case fragments and larger chunks of material are available in the collection below!