Surely concrete doesn't last 65 million years?
65 million years is an incredibly long time. I don't think any of you are grasping the scale of time here. What would rebar-reinforced concrete look like after deep burial and metamorphosis at high temperature and pressure for that long? Assuming it would be recognizable and easily stumbled upon by archeologists or paleontologists is naive.
Well, granted, I AM making the assumption that there are things in our civilisation that will last longer than mere old BONE, but if you can find some source that shows that human bones will be the last traces left of our civilisation, please feel free to post it and I'll retract my claim.
However, I think it's safe to say that rebar-reinforced concrete, or cast iron, or titanium mountainb ike frames, or whatever would survive significantly better than a human bone would under the same conditions.