Probably buried under deep soil somewhere. Neglected historical sites get lost to nature incredibly fast. Doubt anyone pre 20th century thought this random hill in Mexico wouldn't've been hiding the Teotihuacan pyramid constructed 1800 years ago.
It's worth noting that some people believe that naaso hablood overseeing hargaysa to be some type of pyrmid as well. I've heard rumors that locals discovered some kind of chamber near the hills but are too scarred to go inside themselves. Probably cap but its cool to think about