You are looking at the second of the two Boeing 747 space shuttle carriers being taken to its resting place at the Joe Davies Heritage Airpark, in Palmdale, California. After two decades ferrying the space shuttles across the country, the two legendary aircraft are now retired.
Over the next 20 years, it made 66 flights with a shuttle atop its fuselage, including 17 missions in which it ferried shuttles from NASA's Dryden (now Armstrong) Flight Research Center after landings at Edwards Air Force Base to the Kennedy Space Center on Florida's east coastline. Upon its retirement on Feb. 8, 2012, it had amassed 33,004 flight hours over its 38-year flight career.
Here are a few shots and a video of one of the coolest airplanes to ever fly the skies. [Sploid]