You referred to the Hoover Dam, great achievement of the '30s. You couldn't build the Hoover Dam today because they'd discover a snail darter in the Colorado River and would stop it.Exactly.
A non-government item that comes to mind from the 30's is the Empire State Building. The whole thing went up in 18 months. The 9/11 attacks were almost 10 years ago and we still don't have completed buildings at Ground Zero. You couldn't build another Empire State Building in 18 months today - just getting through all the regulatory hurdles and environmental impact statements would probably take five years all by themselves.