Mexico has restored a series of colorful 2,500-year-old cave paintings with help from the American archaeologist who first registered them almost 50 years ago.

The striking red, ochre and turquoise-blue paintings now show their remarkably bright colors, after a 12-year restoration effort by Mexican government archaeologist Sandra Cruz.

Cruz noted this week that she got invaluable help from Dr. David Grove, Professor Emeritus of Anthropology at the University of Illinois at Urbana-Champaign.

Grove first registered the Olmec cave paintings near the hamlet of Oxtotitlan, in southern Guerrero state, in 1968. They had once been previously mentioned in an obscure travel book.

By the 1990s, neglect, graffiti and mineral stains hid some paintings.

Cruz said Grove "went with us on the first trip. He told us, 'behind that mineral stain is a such-and-such painting. He helped us a lot because the cave is complex and had changed a lot."

Grove said he first found the cave paintings — which had been known to locals for years, and were sighted by a friend collecting rocks — and sketched them in 1968.

Locals at the time were throwing rocks at one of the cave's main paintings, because they believed it was a depiction of the devil.

In fact, Cruz says, they depict a human-like figure sitting atop a depiction of the 'earth monster,' a symbol of the underworld. Cruz interprets the figure as "an entreaty for rain and fertility."

Grove said "I made up a story, I told them it's the rain god, and if you destroy it you're going to lose all your water supply and they bought that, and they quit throwing rocks at the painting."

Since then, locals have become increasingly aware and protective of the paintings.

"The other good thing is that the people of Oxtotitlan now really care for the paintings," Grove said. "Instead of throwing rocks at it, they carefully screen who is coming through, they sort of are the guardians of Oxtotitlan, and they can be rightfully proud."

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This story corrects the American archaeologist's first name to David.