How do I replicate a section of Google Maps terrain into unity?

i don't think google maps contain heightmap information (that is to say, any terrain imported via google maps would be flat)

google nasa global heightmap data click ASTER

something like this would be used to zoom in picking a specific area and cutting it out and using it as a heightmap. There are other heightmap data sets as well. this is just one of the few global ones. That will of course only get you the heightmap, the terrain will still need to be decorated with foilage and textures but it will look similar as terrain.

As for the decoration, you could use google maps to inspire you as to what kind of trees or foilage to use, perhaps also including some google searches on that regions common plants and trees.

But at the end of the day, you can get a realistic heightmap (roughly) and then at that point you have to use your own interpretation of satellite images to build it up.

If you wanted the actual buildings and such included in the heightmap and roads and such, that's technically doable but you'd probably have to contract out to a professional company to create a high res image of that area for you.

1 foot accuracy height maps of the global are simply faaaar to much time and effort and storage to be public resources or even feasible. You create those as needed.