The push to fully excavate the site did not come until late in the 20th century. On 21 February 1978, workers for the electric company were digging at a place in the city then popularly known as the "island of the dogs". It was so named because it was slightly elevated over the rest of the neighborhood and, during flooding, street dogs would congregate there. Just over two meters down, the diggers struck a pre-Hispanic monolith. This stone turned out to be a huge disk of over in diameter, thick and weighing . The relief on the stone was later determined to be Coyolxauhqui, Huitzilopochtli's sister, and was dated to the end of the 15th century.