Victor Green, a Black mail carrier who lived in Harlem, was frustrated when he continually faced racism while traveling around the country in the 1930s.

Hoping to protect himself and other Black travelers, Green came up with a guide that would make it easier to find safe places around the U.S. This guide, known as The Negro Motorist Green Book, became widely popular after it was published in 1936, according to a report from Madeline Hellmich, a graduate student at Indiana University–Purdue University Indianapolis.

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Now, a group of historians in Colorado are aiming to make sure Green Book sites are recognized by State and National Registers of Historic Places. According to CBS News Colorado, History Colorado has already taken the first step by holding community meetings to gather input from residents. The public is getting a chance to ask questions, add suggestions and share information they may already know about Green Book sites.

Terri Gentry, History Colorado’s Engagement Manager for Black Communities, said the researchers have received an Underrepresented Community Grant to document the sites.

“So, you can go down to Pueblo, Colorado and find a place that’s registered. They were safe spaces for our family members and community members when they were traveling around the state,” Gentry told CBS News Colorado.

She continued, “This is offering a perspective on history that a lot of folks aren’t aware of. It helps to understand part of that story with travel and some of the experiences that we had. We wanted to get out and explore the country. We wanted to get out and take advantage of all that the country had to offer. The Greek Book sites offered that.”

Gentry, a Colorado native, said the project honors her own family and experiences.

“I want to celebrate who they are and showcase the work that they’ve done to make our community place and space,” she said.

According to Hellmich’s report, Green made his books available nationally and affordable after instantly seeing a high demand for the guide. The Harlem native’s guide was sold in Black churches and gas stations.