Walking Derricks

The rig that is shown in this posting
(http://wallihan.blogspot.com/2013/01/drake-rig.html) drills 6 wells
from one location. Then they tear the whole thing down, pack it up in
trucks, move to another location and do it again.

To get between the six well locations, the derrick has four "feet",
one of which is shown here. To move the derrick the extend downward
to raise the rig off the ground, then move horizontally to move the
rig about 6 feet at a time.