It's interesting trying to compare this to Long Now. The article mentions his 'Double Negative' from ~1970 and that it's already badly decayed (a look on Google

It's interesting trying to compare this to Long Now. The article mentions his 'Double Negative' from ~1970 and that it's already badly decayed (a look on Google Maps supports this) after barely 40 years. It doesn't give much detail about the City, but the illustration (photo?) suggests that its most prominent features are mounds of unreinforced concrete. The famous Sandia study on long-term building that Long Now and Steward Brand often cites finds that unreinforced concrete does very poorly over the long run, and that to last, concrete needs to be reinforced and mixed extremely dryly with tons of manual labor (one reason Roman concrete has lasted so long); Heizer is doing this with a skeleton crew and must take shortcuts. So it sounds like the depressions are going to fill in quickly on a 10,000 year timescale and the exposed concrete is going to break down on the order of centuries. It might last a relatively long time in a buried form like Mayan pyramids, but not as an artwork with integrity, and I doubt much will be left at all by 10,000 years.