Santa Rosa Island

Florida

80th National Monument

9,500 Acres

Established by Presidential Proclamation: May 17, 1939 by President Franklin Roosevelt

Abolished as a National Monument: July 30, 1946 by the 79th Congress

Authorized as a National Seashore: January 8, 1971

This is an "in and out" monument. I am not sure why the National Park Service does not have it on their list of abolished monuments. Perhaps it is because the island eventually did return to the NPS system.

The monument was diminished by 4,700 acres on August 13, 1945 by President Harry Truman, abolished in 1946, and then brought back into the NPS system on January 8, 1971 with the creation of the Gulf Islands National Seashore.

Wikipedia says, "... the county returned the island to the federal government in the expectation that it would be developed as a U.S. National Monument preserving the remnants of Fort Pickens. The fort and other areas are now preserved within the Gulf Islands National Seashore. "

Wikipedia: Santa Rosa Island (Florida)

Considering Fort Pickens to be outdated, the U.S. War Department sold Santa Rosa Island in 1929 to Escambia County, Florida, for US$10,000. Ten years later, the county returned the island to the federal government in the expectation that it would be developed as a U.S. National Monument preserving the remnants of Fort Pickens. The fort and other areas are now preserved within the Gulf Islands National Seashore.

On July 8, 1950 the federal government conveyed an 875-acre (3.54 km²) parcel of Santa Rosa Island with 3 miles (4.8 km) of Gulf frontage to Okaloosa County. The county paid the federal government $4,000 to complete the transaction, which was supported by Congressman Bob Sikes.^[2] The portion of Santa Rosa Island transferred is now known as Okaloosa Island. The twelve-mile (19 km) long beach road onto U.S. Air Force property, west of the Okaloosa Island portion of Santa Rosa Boulevard, was unguarded and accessible into the 1980s, but heightened security concerns have since led to it being guarded or blocked at all times. Various military missile launch and test facilities exist on Santa Rosa Island south and southwest of Hurlburt Field.

https://en.wikipedia.org/wiki/Santa_Rosa_Island_(Florida)

Wikipedia:

https://en.wikipedia.org/wiki/Santa_Rosa_Island_National_Monument