How long would cities be recognizable after a nuclear war?

Question

In 2068, a nuclear war is fought between the USSR and the USA. 42,000 best bombs are used, and 2,000 megatons are used during the war.

My story takes place mostly in 4 regions of the United States, the southeast, Midwest, southwest, and northwest. It’s been 20 generations since the war, and most people live in small, farming communities, or United city states. There are three powerful nations in the post apocalyptic United States called the Midwestern empire, the Western Federation, and the Florida Republic.

My main character is searching for a large city out in California, that used to be known as Los Angeles. My question is, would this city still be recognizable after 500 years?

By recognizable, I mean: Could you be able to tell a city was once there just by looking forward at it? BTW, just assume that the cities weren’t hit directly by bombs.

Answer 1

There is a movie "Life after people" that elaborated into the topic with great detail, math and science. Big buildings will all topple in a century, smaller ones may stand for a few thousand years, if made from stone. Some landmarks, however, may safely wait for a new civilisation. Those are pyramids, Rushmore mountain, some cliffside monasteries. But they would be hardly recognisable at the point. Just some traces of artificiality.

Answer 2

Well, I'd have to imagine that in any major nuclear exchange between Russia and the U.S., high-profile targets like Los Angeles would be hit directly several times over. It's the ejection of debris from cities into the stratosphere which would cause the nuclear winter that is feared by scientists.

If, however, we say that Los Angeles were not hit and other major cities were -- thus triggering the nuclear winter scenario -- Los Angeles would likely be recognizable for millennia. The buildings, even left unmaintained, would stand for centuries and their foundations, the streets, the sewage systems, the LA River, etc. would endure for much longer than I would expect the human race to survive at that point. Archaeologists have found human settlements as old as 13 millennia made with vastly inferior technology.

If L.A. were to take several direct hits, however, we might expect that all or almost all of the buildings would be gone, though their debris, the roads, and sewer systems would still leave traces. Over time, especially with the deposition of all of the ash that we might expect in the wake of a nuclear holocaust, it may all be buried. But traces would live on for the foreseeable lifetime of the planet.

As an aside, I'd imagine that farming would be nearly impossible and the prevalence of radiation, both at the surface and in the atmosphere would make human life untenable.

Answer 3

No.

Why not? Because by whom and by what they would need to recognize LA?

For me the only distinctive landmark of LA is Griffith Observatory ( I omit Hollywood sign as this is something that can be overrun by vines in 2 seasons).

20 generations is 400 years (using old method, new one would give you between 500 and 600).

So you need to go back to XVII century and look for building that were abandon around that time and not tended to in 400 years. Usually the castles build in manner similar to observatory are in very bad shape (if noticeable at all). La is famous for it's wild fires. Just imagine that after the war there is one like last year and no firefighters to deal with it. How much is left of LA? And after 100 years? What about 400 years and a fire each 100 years?