I was reading some old NTS documents yesterday regarding their
borders being breached. Some guys got very far (U1a) into the site on
bicycle.
I think you could get very far beyond the border of Groom Lake on a
mountain bike. The first level of security doesn't appear to be a
tight perimeter, but rather choke points. But if you got close to the
base, I'm sure there is a real secure perimeter.