From "Voices of the Manhattan Project," 2005 Interview with Stirling Colgate
Before any of the important visitors arrived, we knew that the decision had been made that this would be a laboratory. About a month or two earlier, a “mega-bulldozer” came through the place and set about redoing things—roads and everything else. The construction work was being done at a tremendous rate.
There were four of us who were seniors at the Los Alamos Boys Ranch School. To fill in for one of the faculty, I was teaching the math class. We knew the school was going to be closed because of the war. I mean you just felt it. But we were all wondering why the government would put anything up here on the mesa. It was so hard to get water and there was no good transportation or railroads nearby and so on. It was just a crazy place to do any war thing. Secrecy? You would do so much better, if secrecy is what you want, to locate it in the middle of a military compound. Just anything else.
So we used to kid from the very beginning about what kind of science-fiction laboratory they might have here with white-coated scientists. Then these two guys show up, one wearing a porkpie hat and the other wearing a fedora, a hat that we thought was uniquely E. O. Lawrence. Of course the porkpie, there was just no question that this was Oppenheimer.
We knew enough from physics class and publications of the current physics issues that fission could be used to make a chain reaction. So when those two showed up after this place had already been run over by the mega-bulldozer, there was absolutely no question in the mind of a couple of us smart ass kids that this meant that they would be making a nuclear bomb.