For decades, an unmarked cemetery sat undisturbed, tucked away at the edge of a Florida high school campus.

But last week, Hillsborough County school district officials announced that the burial ground had been found with help from ground-penetrating radar scans. The radar bounced back with evidence of about 145 coffins, buried just a few feet beneath the surface.

The discovery of what appears to be the Ridgewood Cemetery, where mostly African-Americans were buried in the 1940s and 1950s, on what are now the grounds of C. Leon King High School was a sad but important reminder of the city’s suppressed history, said Yvette Lewis, the president of the county branch of the N.A.A.C.P.

“The city of Tampa — and Hillsborough County itself — has pretty much erased and eradicated African-American history,” she said. “Now we feel as though our ancestors are coming back and talking to us and saying, ‘Hey, tell our story.’”