Why is the Vredefort Dome difficult to recognize as an ancient crater from the ground?

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four impact craters — Meteorite crater Four impact craters of the same size (30 km [20 miles] in diameter) imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. The images are oriented such that the craters appear illuminated from the left; the Venusian crater is imaged in radar wavelengths, the others in visible light.

The Vredefort Dome is difficult to recognize as an ancient meteorite crater from the ground primarily because billions of years of weathering have caused the surrounding crater structure to erode away.1

Because the original crater rim and features have been worn down over time, the site is now classified as an impact structure rather than a clearly defined crater. While the dome itself consists of granite that shifted upward at the center of the impact site, its origin was historically debated; it was once mistakenly thought to be volcanic in nature. The true nature of the site was only confirmed through the identification of shatter cones—conical rock structures created by intense shock—which indicate the immense pressure of a massive impact.1