Many Black cemeteries in United States' Houston have been washed away by a nearby bayou (marshy outlet) during major storms in past decades.

Under the blazing Texas sun, dozens of volunteers mowed grass and cleaned tombstones recently to help save what is left of Olivewood Cemetery's 4,000 graves.

Some parts of the cemetery at first appear forgotten, with broken or dirty headstones.

But the graveyard is receiving newfound care – part of a modern push to preserve Black heritage, as interest in saving neglected or even erased African-American historical sites spikes.

The "George Floyd murder, I think it just was a crystallizing moment," said Antoinette Jackson, a professor of anthropology at the University of South Florida, explaining the new interest in such places.

African-American cemeteries "have been continually erased and information about them silenced," she said.

Margott Williams, president of the Descendants of Olivewood nonprofit, laments those whose graves have washed away at the Houston cemetery: "There were babies back there. I don't see my babies back there anymore. There were veterans back there. I don't see my veterans back there."

To help record the existence of such sites, Jackson created the Black Cemetery Network, which allows people to share the location of African-American graveyards, many of which have been lost to time and neglect.

The reasons for the cemeteries' disappearance from public knowledge are many.

The oldest plots hold enslaved individuals, who were generally buried on white people's land. Those white people did not systematically record the graves' existence, and subsequent landowners, if they knew about them, often ignored them.

Other Black cemeteries have been claimed by local government land grabs in which the community's rights to their burial grounds weren't respected, Jackson said.

Such was the case in Tampa, Florida, where Mayor Jane Castor earlier this year apologized for the city's confiscation of two cemeteries from the Black community to resell in the 1930s to white developers.

In the suburbs of Washington, an attempt to sell to an investor land that was once a slave cemetery is attracting attention, with various groups mobilizing against the move.

And finally, many cemeteries were forgotten after African-Americans were driven from nearby areas due to the construction of infrastructures such as highways or outright gentrification.

At Olivewood Cemetery, a single African-American family still lives nearby in a modest house that is now surrounded by high-end buildings.

The graveyard was only recently classified among the country's most endangered historic places by the nonprofit National Trust for Historic Preservation.

The move comes decades after Charles Cook first rediscovered the cemetery in 1993 after it was more or less abandoned for 40 years.

"It was a jungle," he told Agence France-Presse (AFP).

Machete in hand, he cleared it himself and continuing its upkeep at his own expense, visiting the graveyard every day. In researching its occupants, he discovered two of his ancestors were buried there.

A study will soon propose solutions to protect it from the dangers of eroding rainwater and the bayou. How the work will be financed remains to be seen, however.

Nationally, in February, an African-American Burial Grounds Preservation Act was introduced in the U.S. House and Senate "to research, identify, document, preserve, and interpret historic African-American burial grounds," which Jackson thinks will be adopted in the fall.

In the meantime, on Saturday, anthropology student Jasmine Lee was supervising the Olivewood volunteers.

She says she is fascinated by the tombs which testify to "cultural, spiritual ideals that were not only founded in practice during enslavement but carried over into freedom."

Some of the tombstones' script is written upside-down or in reverse to trick evil spirits or otherwise allow the dead to read their names from below.

Elsewhere, shells were used as decorations to evoke a sea voyage, which in some parts of Africa symbolizes departure to the other side.

Further down the way, iron pipes in the ground no doubt helped the spirits get out and amble about.

In Sugar Land, a suburb southwest of Houston, a memorial is in the works to honor 95 African-Americans whose graves were found in 2018 during construction work on school district grounds.

The skeletons, as it would turn out, belonged to prisoners who died between 1878 and 1911 and who had been loaned out by judicial authorities to work the local sugarcane farms.

The work was grueling and the convicts' poor health was evident from the state of their bones.

The "convict leasing system," as it was called, was abolished in Texas in 1912 and at the federal level in 1941.

Shifa Rahman, campaign director for the Convict Leasing and Labor Project, is advocating for the forthcoming memorial to "properly and equitably" educate about what the prisoners "had to endure under the convict leasing system."

The nonprofit is also calling for DNA tests to identify the remains.

For now, everyone has an identical tombstone, on which "unknown" is written, followed by a number.