A century ago this week, the wealthiest U.S. Black community was burned to the ground.

At the turn of the 20th century, the Greenwood District of Tulsa, Oklahoma, became one of the first communities in the country thriving with Black entrepreneurial businesses. The prosperous town, founded by many descendants of slaves, earned a reputation as the Black Wall Street of America and became a harbor for African Americans in a highly segregated city under Jim Crow laws.

On May 31, 1921, a white mob turned Greenwood upside down in one of the worst racial massacres in U.S. history. In the matter of hours, 35 square blocks of the vibrant Black community were turned into smoldering ashes. Countless Black people were killed — estimates ranged from 55 to more than 300 — and 1,000 homes and businesses were looted and set on fire.

Yet for the longest time, the massacre received scant mentions in newspapers, textbooks and civil and governmental conversations. It wasn’t until 2000 that the slaughter was included in the Oklahoma public schools’ curriculum, and it did not enter American history textbooks until recent years. The 1921 Tulsa Race Riot Commission was formed to investigate in 1997 and officially released a report in 2001.

“The massacre was actively covered up in the white community in Tulsa for nearly a half century,” said Scott Ellsworth, a professor of Afro American and African studies at the University of Michigan and author of “The Ground Breaking” about the Tulsa massacre.

“When I started my research in the 1970s, I discovered that official National Guard reports and other documents were all missing,” Ellsworth said. “Tulsa’s two daily white newspapers, they went out of their way for decades not to mention the massacre. Researchers who would try to do work on this as late as the early 1970s had their lives threatened and had their career threatened.”

In the week following the massacre, Tulsa’s chief of police ordered his officers to go to all the photography studios in Tulsa and confiscate all the pictures taken of the carnage, Ellsworth said.

These photos, which were later discovered and became the materials the Oklahoma Commission used to study the massacre, eventually landed in the lap of Michelle Place at Tulsa Historical Society & Museum in 2001.

“It took me about four days to get through the box because the photographs were so horrific. I had never seen those kinds of pictures before,” Place said. “I didn’t know anything about the riot before I came to work here. I never heard of it. Since I’ve been here, I’ve been at my desk to guard them to the very best of my ability.”

The Tulsa museum was founded in the late 1990s, but visitors couldn’t find a trace of the race massacre until 2012 when Place became executive director, determined to tell all of Tulsa’s stories. A digital collection of the photographs was eventually made available for viewing online.

“There’s still a significant number of people in our community who don’t want to look at it, who don’t want to talk about it,” Place said.

For Black Tulsans, the massacre resulted in a decline in home ownership, occupational status and educational attainment, according to a recent study through the 1940s led by Harvard University’s Alex Albright.

Today, there are only a few Black businesses on the single remaining block in the Greenwood district once hailed as the Black Wall Street.

This month, three survivors of the 1921 massacre — ages 100, 106 and 107 — appeared before a congressional committee, and a Georgia congressman introduced a bill that would make it easier for them to seek reparations.

Meanwhile, historians and archaeologists continued to unearth what was lost for decades. In October, a mass grave in an Oklahoma cemetery was discovered that could be the remains of at least a dozen identified and unidentified African American massacre victims.

“We are able to look for signs of survival and signs of lives. And really look for those remnants of built Greenwood and not just about how they died,” Odewale said. “Greenwood never left.”

— CNBC’s Yun Li is also co-author of “Eunice Hunton Carter: A Lifelong Fight for Social Justice.”