That was where the motley sediments of ancient Mars were succeeded by layer upon unvarying layer of brownish rock, two miles high.

NEWYORKER: The Martian Chroniclers

"We have not found any ancient objects linked to the context, and because the paintings are on ravine walls and in the rainy season the sediments are washed away, all we have is gravel, " said archaeologist Gustavo Ramirez, from the Mexican National Institute of Anthropology and History (Inah).

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