This is the Complex 26, Pad B gantry: one of the sights at the Air Force Space & Missile Museum. On January 31, 1958, America's first satellite was launched from Pad A at this Complex, using a rocket and gantry that looked just like the ones here. The 30 pound Explorer I satellite was placed in orbit by a Jupiter-C rocket. The Jupiter-C was a modified Redstone (the same rocket which would later be used in the Mercury program). 

The gantry shown here is mobile; prior to launch, it was moved away from the vehicle on rails. The vehicle shown in the picture is a Redstone rocket. 

Roughly 400 feet away, northwest of this gantry, is the blockhouse.