Hi,
I had never heard of the Douglas Proving Grounds and I think a few others may not have either, but here's an interesting peice of its history:
On January 26, 2011 Dugway Proving Ground was placed on lockdown. Al Vogel, a public affairs specialist for the installation, would only say that the lockdown began at 5:24 p.m. Employees were not allowed to leave, and those coming to work were not allowed in. Vogel said there were no injuries, no damage and no threats reported at the proving ground. There were about 1,200 to 1,400 people at Dugway when the lockdown occurred. It was later announced that the lockdown was in response to the temporary loss of a vial containing VX nerve agent. The lockdown was lifted on January 27 following recovery of the material
From wiki
Also, from Utah News
The Army and civilian employees at Dugway conduct tests on systems to defend against chemical and biological weapons, as well as tests on smoke and obscurants. They also test meteorological devices. Several thousand sheep mysteriously died in Skull Valley in 1968, with nerve gas from Dugway the suspected culprit.
So you're right. There is something going on out there. Perhaps legit, but if we can find out a little more about the planes going in and out there might be more to this story.
Peace

